UNIFYING THEMES OF LIFE o plants obtain most of their necessary

chemicals from the soil, water and air

THEMES OF LIFE o animals acquire most of the chemicals
- basic ideas that apply to all organisms they need by eating plants or other
- connects many things in the exploration of life animals
o chemicals are returned to the soil by
1. BIOLOGICAL SYSTEMS bacteria and fungi that decompose the
 SYSTEM wastes and remains of living
- has properties/ functions based on the organisms
arrangement and interactions of its parts - Interaction of organisms with each other and
together, the parts of our body enable us to with the nonliving environment put the system
move in ecosystem
Example: Organ System “The biological systems theme applies to all levels of
- contraction of muscles attached to bones life from the biosphere all the way down to the
causes movement molecules in cells”
- blood vessels then supply these parts
with oxygen and food 2. THE CELLULAR BASIS OF LIFE
 Ecosystem - All organisms are made of cells
- organisms in the ecosystem require a steady - Levels of organization:
supply of certain chemicals to live
o cell
o tissue
o organ
o organ system
o organism
- Most multicellular organisms have cells that - The offspring inherits units of information
are specialized for different functions called genes from their parents
- A multicellular organism’s development and  Genes:
survival are based on the functions and - Responsible for family resemblance
interactions of its many cells - Made up of information-rich molecules called
 Muscle cells DNA
- Contract and enable us to move  Each cell in the body contains a copy of all
 Nerve cells DNA that were inherited from our mother and
- Transmit impulses that control our muscles father
“The cellular basis of life is a theme you will - When a cell divides, it copies its DNA and
encounter often as you explore the living world” passes this genetic information on to each of
the two cells it produces
3. STRUCTURE AND FUNCTION  In humans, an egg cell from the mother fuses
- The relationship between structure and with a sperm cell from the father
function is apparent in the entire organism and - This results in a fertilized cell containing a
the physiological systems that serve them combination of DNA from both parents
- The structure determines function, function - The inherited DNA directs the transformation
reflects structure of the fertilized egg into a person with his/her
– Technically, they are inseparable own eye color, facial features and other
 The structure of the bird’s bones contributes to characteristics
the bird’s ability to fly  The inherited information in the form of DNA
Inside the bones, an open, honeycomb- like enables organisms to produce their own kind
structure provides great strength with little weight
Birds have long extensions of nerve cells that 5. ENVIRONMENTAL INTERACTIONS
control their flight muscles  No organism is completely isolated from its
These fibers make it possible for the bird’s brain to surroundings
coordinate flying movements  As part of an ecosystem, each organism
 Homologous Structures interacts continuously with its environment
- Structures that are shared by related species - The plants obtain water and nutrients from the
and that have been inherited from a common soil, carbon dioxide from the air and energy
ancestor. from sunlight
 The transfer of chemicals between organisms
4. REPRODUCTION AND INHERITANCE and their environments is a key process in any
 “Like begets like” ecosystem
 - Breathing air, drinking water, eating food and environment through the process of natural
getting rid of wastes are chemical exchanges selection
with the environment o Some animals make their coats
 There is a constant sensing and responding to lightened to facilitate hiding from
changes in the environment predators
- The specialized leaf of the Venus flytrap  The study of evolution is helping health
senses the light footsteps of a soon-to-be- professionals understand how disease-causing
digested fly bacteria become resistant to antibiotic drugs
- The plant responses by rapidly folding the leaf  Environmental issues such as water and air
together pollution are changing how people think about
 There is a constant sensing and responding to their relationship with the biosphere
changes in the environment  The population then evolves with its need for
- The sun may cause organism to squint survival
- The bark of an approaching dog causes you to - Darker beetles are more likely to survive
turn your head quickly longer and reproduce, passing their genes on
to more offsprings
6. ENERGY AND LIFE  Great diversity exists among the three domains
 Moving, growing, reproducing and other of living things:
activities of life require energy - Bacteria, Archaea and Eukarya
 Energy is obtained from chemical reactions o Evolution explains this diversity
- Sugars, fats and other “fuel-like” molecules in  Charles Darwin and Alfred Wallace
the food produce energy - Worked on the idea of evolution by natural
 Energy enters the ecosystem as sunlight selection
- Plants are producers that convert light energy
to chemical energy stored in food 9. SCIENTIFIC INQUIRY
- Animals and other consumers obtain their  Involves asking questions about nature and
energy in chemical form by eating then using observations or experiments to find
- Energy exist in the ecosystem as heat, which possible answers to those questions
all organisms generate as they perform work - By fitting a radio transmitter onto an Atlantic
 Because all organisms lose energy in the form turtle, researchers can monitor its movement
of heat, an ecosystem cannot recycle energy. - This can help researchers determine how large
“Life on Earth depends on a continuous supply of a nature preserve must be to support a
energy from the sun” population
 Modern biology is changing humans’
7. REGULATION everyday lives
 Organisms have the ability to regulate their - New findings about the DNA affect medicine
internal conditions and agriculture
- The thermostat of the brain reacts whenever - Research on the nervous system is improving
your body temperature varies slightly from the treatment of certain mental illnesses
37◦C - The result of stem cell research, animal
- It then sends signals to the skin to produce cloning, environmental issues, genetically
sweat. Sweating helps cool the body modified crops or new ways to treat disease
- Panting is another example of cooling show the impact of biology
mechanism. It causes moisture from the
surface of the lungs to evaporate 10. SCIENCE, TECHNOLOGY AND SOCIETY
 The ability of mammals and birds to regulate  Technology applies scientific knowledge in
body temperature is another example of new ways
homeostasis or “steady-state” - In 2013, Australia developers created a
 Different mechanisms enable organisms to prototype for a bionic eye.
regulate their internal environment despite - It sends an image to a microchip in the brain,
changes in their external environment allowing the user to “see” the image
 Through science, humans learn about the
8. EVOLUTION AND DIVERSITY solution to various problems
 Explains changes in organisms over long  The scientific method is able to give
periods of time direction and pace for every inquiry
- Adaptation allows life forms to acquire new  Technology produced machinery to lengthen
characteristics in response to their the life of perishable goods

Life and Its Beginnings

Early Beliefs About the Origin of Life
 People were puzzled about how life originated on Earth centuries ago.
 Spontaneous Generation – Also known as Abiogenesis. States that life originates from nonliving matter.
 The Idea was proposed by Aristotle in the fourth century and held its position as the belief of origin of life
until the seventeenth century.
 People in the past believed that flies can grow from cattle manure, mice from wheat stored in the dark,
maggots from decaying meat and fish.
 As time passed by, scientists began to question this belief and began to explore opposing idea called
Biogenesis.
 Biogenesis – the belief that life originates from preexisting life.
 Since then several experiments have been conducted to prove these contradicting beliefs to explain life.

Redi’s Experiment
 In 1668, the Italian physician Francesco Redi conducted an experiment that challenged the spontaneous
generation.
 His experimental setup involved rejecting spontaneous generation using maggots that arose from decaying
meat.
 He designed the experiment using two set of jars that were identical, but one jar has a gauze covering.
 Redi observed that flies were attracted to both jars. However, the flies settled only on the meat in the open jar.
 Redi observed that maggots arose from eggs laid by flies on rotten meat but not on the meat and concluded
that maggots were not products of spontaneous generation.

Needham’s Experiment
 In 1748, English Priest John Needham challenged Redi’s experiment.
 It was common knowledge at that time that boiling can kill microorganisms.
 Needham’s experiment tested whether or not microorganisms can appear spontaneously after boiling.
 He placed a solution of boiled mutton broth in a container and heated it. Then he sealed it with corks proving
that it could prevent anything from the environment to enter the flask and generate life.
 After several days, Needham observed that the broth turned cloudy due to microorganisms.
 He concluded that life in the broth was caused by spontaneous generation.
 In actuality, he did not heat it long enough to kill all the microbes in the broth.

Spallanzani’s Experiment
 Lazzaro Spallanzani, an Italian scientist, challenged Needham’s experiment.
 He boiled a broth containing meat and vegetable placed in clean glass containers. Both containers were boiled
but one setup was not sealed, allowing air to enter the flask.
 Several days later the container was filled with a population of microorganisms, while the sealed container
remained sterile.
 He concluded that life occurred from something that entered the unsealed flask and that it was responsible for
life to grow.
 The results were not taken by the abiogenesis believers. They also claimed that Spallanzani excluded air
which they believed was needed for spontaneous generation to occur

Pasteur’s Experiment
 1861 – Louis Pasteur’s experiment proved that Spontaneous Generation does not occur.
 Pasteur designed an experiment to test the idea a vital element of air was necessary for life to occur.
 He boiled sugar solution with yeast in flasks with a long, curved neck (Swan-neck flask).
 The flask were remained open in order for air to enter, but no organisms developed in the mixture.
 He also cut the neck of the flask to. Within two days, the solution became darker because airborne
microorganisms were able to enter.

Current Beliefs About the Origin of Life

 Divine Creation – The oldest hypothesis that life came from a divine being is the most widely accepted
belief. It is believed that life forms and everything in the universe were created through supernatural power
rather than naturalistic means. This belief is also called creationism.
 Spontaneous Origin – Some scientist believed that first life came from a spontaneous origin or life evolved
from inanimate matter.
 Before life has evolved, simple molecules combined to form complex ones. These chemical processes came
from lightning or some form of geothermal energy, culminating in the evolution of cells.
  Scientist also tried to explain various scenarios where the first living organisms where microorganisms that
were formed in underwater vents.
 Panspermia – Swedish scientist Svante Arrhenius popularized the idea that life arose outside Earth and life
forms were transported from another planet to serve as seed of life on Earth.
 Panspermia proposes that a meteor or cosmic dust may have carried to Earth significant amounts of organic
molecules, which started the evolution of life.

Twenty-First Century Biology: A Bird’s Eye View

Biotechnology
 Deals with the application of biological concepts and systems to make products beneficial to man.
 It uses basic molecules of life to make new products, It is currently being used in many areas such as business,
agriculture, bioremediation, food processing, energy production, medicine, and pharmaceuticals.
 This is not a new field for it has been used for decades in the manufacturing of beverage, cheese, bread and
milk.
 In the Philippines, traditional biotechnology is used in the production of nata de coco, bagoong, patis, kesong
puti, local wines, and vinegar.
 Today, biotechnology encompasses manufacturing processes that include the advances in genetic engineering
such as recombinant DNA technology, monoclonal antibodies, and bioprocess technology.
 It applies to any technique that manipulates it mimics natural process to improve one’s physical and economic
well-being.

Other Use of Biotechnology

 In medicine, biotechnology is used in the production of medicines and supplements.
 The most common example is insulin that is synthetically produced using E.coli.
 Transgenic animals are also products of biotechnology. There are pigs with humanized organs to be used for
human organ transplantation.

Products of Biotechnology
 Biotechnology has led to the birth of Dolly, the world’s most famous sheep cloned from an adult somatic cell,
who was her firstborn lamb named Bonnie;
 Miller, the first cloned pig; and Polly, the first transgenic lamb cloned by nuclear transfer.
 Cloning
 Biomimicry is the science of applying nature-inspired designs in human engineering and invention to solve
human problems. It was used to create the first flying machine, inspired by eagles and owls—this paved the
way for technologies like jets and planes.

The Cell and Its Beginning

The Discovery of Cells

 Robert Hooke – He devised one of the earliest microscopes that can magnify every sort of material he can
find at that time such as glass, crystal, point of a pin, body of a flea, and even frozen urine.
 Hooke’s most commemorative work came from a thin slice of cork from a bark of an oak tree, he describe it
as perforated and porous surface and called it cellulae.
 He drew what he observed and his drawings were collected in a manuscript called Micrographia.

 Antonie van Leeuwenhoek – a Dutch naturalist, was credited to be the first to study magnified cells.
 His interest came when he got hold of a copy of Hooke’s Micrographia, and even devised his own
microscope,
 He used his skill to devise more than 500 lenses during his lifetime in which one of his lenses was able to
magnify 270 times and was able to make a more detailed drawing.
 Though he did not use the word “cell”, he gave the name animalcules.

The Cell Theory

 While working with his microscope, Matthias Jakob Schleiden discovered the plant cell out of which
vegetative/meristematic tissues and embryonic plants originated.
 Theodor Schwann discovered animal cells, particularly muscle and nerve fiber tissues now named as the
Schwann cell in his honor.
 Along with the findings of other scientists, they confirmed that cells are fundamental units of life.
  Rudolf Virchow was the proponent of the Cell Theory’s 3rd postulate, which states that all cells come from
pre-existing cells through the process of cell division.

The Three Postulates of the Cell Theory

1. All living things are made of one or more cells.
2. The cell is the smallest unit of life.
3. All new cells come from preexisting cells.

I. Unicellular Organisms II. Multicellular Organisms

a.) Amoeba a.) Fungi
b.) Bacteria b.) Plant cells (Douglas fir tree wood stem cells)
c.) Euglena c.) Animal Cells (red blood cells of chicken)
d.) Paramecium d.) Human cells (red blood cells)
e.) Protozoa

a.) Breast Cancer Cells

- the cell is the basic unit of life in all living organisms including cancer cells and disease-causing cells like bacteria
and fungi.
b.) Human embryonic stem cell
- embryonic stem cells (the latest in research and technology) are being used to treat leukemia and skin cancer and for
newborn screening, aesthetic transplants, and assistive IVF babies.
c.) Skin Cells
- all cells come from pre-existing cells. The skin as a body organ starts on the outside as squamous cells of the
epidermis which become stratified layers of squamous epithelial tissues of the dermis.

Microscope: Parts and Its function

THE DEVELOPMENT OF MICROSCOPE

• 1609 Galileo Galilei
• He perfected the device known as telescope, which is used to magnified objects.
• 1600’s Zaccharias Janssen and Hans Lipperhey
• They are noted as the first men to develop the concept of compound microscope.
• By placing different types and sizes of lenses in opposite ends of tubes, they discovered that small
objects were enlarged.
• 1600’s Anton Van Leeuwenhoek
• He made an improvement to the first microscopes.
• His microscope had one lens and could magnify an image about 270 times its original size.

TYPES OF MICROSCOPES
• Light Microscope – use light and lenses to enlarge an image of an object. A simple light microscope has only
one lens.
• Compound Microscope – a light microscope that uses more than one lens to magnify an object. It magnifies
an image first by one lens, called the objective lens. The image is then further magnified by another lens
called ocular lens.
• Electron Microscope – use a magnetic field to focus a beam electrons through an object’s surface.

Three Main Functions of Microscope

 Magnify an objects with the help of lenses (LPO, HPO)
 Light up the specimen being examined.
 Allow to focus and make the details of the specimen
Other functions of Microscope
 It is used in surgeries, such as cataract surgery and brain surgery.
 It is also used to analyze body fluids, such as blood and urine. They also used it to determine whether the
tissue samples are healthy or diseased.
 It is also used to study evidence from crime scenes.
 It can also be used to identify the type and age of the insects.
 It is also used to examine a fossil and other materials from where the fossil was found.
 It is also used to examine steel for impurities.
 It is used to study jewels and identify stones.
Three Objectives
 Low Power Objectives (yellow line) (10x)
- Almost any feature you need to observe in this course can be located with the 100X total magnification this
objective provides. As an added benefit, the low power objective is always safe to use as it cannot be lowered to the
point of contacting and thus possible breaking a slide.
 High Power Objectives (blue line) (40x)
- This objective (sometimes called the "high-dry" objective) is useful for observing fine detail such as the
striations in skeletal muscle, the arrangement of Haversian systems in compact bone, types of nerve cells in the retina,
etc.
 Oil Immersion Objectives (100x)
- Oil Immersion Objective (100X): This longest objective is used for observing the detail of individual cells
such as white blood cells, the cells involved in spermatogenesis, etc. The lens must be used with a specially
formulated oil that creates a bridge between the tip of the objective and the cover slip. Since the refractive indices of
air and this lens are different, the lens will not work without this special oil.

The Basic Cell Types and Structure

Simple or Complex Cells

Prokaryotes – The first Cells

• Cells that lack a nucleus or membrane-bound organelles
• Includes bacteria
• Simplest type of cell
• Single, circular chromosome
• Nucleoid region (center) contains the DNA
• Surrounded by cell membrane & cell wall (peptidoglycan)
• Contain ribosomes (no membrane) in their cytoplasm to make proteins
Eukaryotes
• Cells that have a nucleus and membrane-bound organelles
• Includes protists, fungi, plants, and animals
• More complex type of cells
Contain 3 basic cell structures:
• Nucleus
• Cell membrane
• Cytoplasm with organelles
Two Main Types of Eukaryotic Cells
• Plant Cell
• Animal Cell

Organelles
• Very small (microscopic)
• Perform various functions for a cell
• Found in the cytoplasm
• May or may not be membrane-bound
Cell or Plasma Membrane
 • Composed of double layer of phospholipids and proteins
• Surrounds outside of ALL cells
• Controls what enters or leaves the cell
• Living layer
• The Cell Membrane is Fluid
• Molecules in cell membranes are constantly moving and changing
Cell Membrane Proteins
• Proteins help move large molecules or aid in cell recognition
• Peripheral proteins are attached on the surface (inner or outer)
• Integral proteins are embedded completely through the membrane
Cell Membrane in Plants
• Lies immediately against the cell wall in plant cells
• Pushes out against the cell wall to maintain cell shape
Phospholipids
• Heads contain glycerol & phosphate and are hydrophilic (attract water)
• Tails are made of fatty acids and are hydrophobic (repel water)
• Make up a bilayer where tails point inward toward each other
• Can move laterally to allow small molecules (O2, CO2, & H2O to enter)

Cell Wall
• Found outside of the cell membrane
• Nonliving layer
• Supports and protects cell
• Found in plants, fungi, & bacteria
Cytoplasm of a Cell
• Jelly-like substance enclosed by cell membrane
• Provides a medium for chemical reactions to take place
• Contains organelles to carry out specific jobs
The Control Organelle – Nucleus
• Controls the normal activities of the cell
• Contains the DNA in chromosomes
• Bounded by a nuclear envelope (membrane) with pores
• Usually the largest organelle
• Each cell has fixed number of chromosomes that carry genes
• Genes control cell characteristics
Nuclear Envelope
• Double membrane surrounding nucleus
• Also called nuclear membrane
• Contains nuclear pores for materials to enter & leave nucleus
Inside the Nucleus
• The genetic material (DNA) is found
o DNA is spread out and appears as CHROMATIN in non-dividing cells
o DNA is condensed & wrapped around proteins forming as CHROMOSOMES in dividing cells
 DNA is the hereditary material of the cell
 Genes that make up the DNA molecule code for different proteins
Nucleolus
• Inside nucleus
• Disappears when cell divides
• Makes ribosomes that make proteins
Cytoskeleton
• Helps cell maintain cell shape
• Also help move organelles around
• Made of proteins
• Microfilaments are threadlike & made of ACTIN
• Microtubules are tube-like & made of TUBULIN
Centrioles
• Found only in animal cells
• Paired structures near nucleus
• Made of bundle of microtubules
• Appear during cell division forming mitotic spindle
 • Help to pull chromosome pairs apart to opposite ends of the cell
Mitochondrion
• (Plural = Mitochondria)
• “Powerhouse” of the cell
• Generate cellular energy (ATP)
• More active cells like muscle cells have MORE mitochondria
• Both plants & animal cells have mitochondria
• Site of CELLULAR RESPIRATION (burning glucose)
• Surrounded by a double membrane
• Has its own DNA
• Folded inner membrane called CRISTAE (increases surface area for more chemical reactions)
• Interior called MATRIX
o Mitochondria come from cytoplasm in the EGG cell during fertilization therefore … You inherit your
mitochondria from your mother!
Endoplasmic Reticulum – ER
• Network of hollow membrane tubules
• Connects to nuclear envelope & cell membrane
• Functions in synthesis of cell products & transport
Two kinds of ER ---ROUGH & SMOOTH
Rough Endoplasmic Reticulum (Rough ER)
• Has ribosomes on its surface
• Makes membrane proteins and proteins for export out of cell
• Proteins are made by ribosomes on ER surface
• They are then threaded into the interior of the rough ER to be modified and
transported
Smooth Endoplasmic Reticulum (Smooth ER)
• Makes membrane lipids (steroids)
• Regulates calcium (muscle cells)
• Destroys toxic substances (liver)
Endomembrane System
• Includes nuclear membrane connected to ER connected to cell membrane (transport)
Ribosomes
• Made of proteins and rna
• “Protein factories” for cell
• Join amino acids to make proteins through protein synthesis
• Can be attached to rough ER or Be free (unattached) in the cytoplasm
Golgi Bodies
• Stacks of flattened sacs
• Have a shipping side (cis face) & a receiving side (trans face)
• Receive proteins made by ER
• Transport vesicles with modified proteins pinch off the ends
• Look like a stack of pancakes
• Modify, sort, & package molecules from ER for storage OR transport out of cell
• Materials are transported from Rough ER to Golgi to the cell membrane by VESICLES
Lysosomes
• Contain digestive enzymes
• Break down food, bacteria, and worn out cell parts for cells
• Programmed for cell death (APOPTOSIS)
• Lyse & release enzymes to break down & recycle cell parts)
Lysosome Digestion
• Cells take in food by phagocytosis
• Lysosomes digest the food & get rid of wastes
Cilia & Flagella
• Function in moving cells, in moving fluids, or in small particles across the cell surface
• Cilia are shorter and more numerous on cells
• Flagella are longer and fewer (usually 1-3) on cells

Vacuoles
• Fluid filled sacks for storage
• Small or absent in animal cells
 • Plant cells have a large Central Vacuole
• In plants, they store cell sap
• Includes storage of sugars, proteins, minerals, lipids, wastes, salts, water, and enzymes
Chloroplasts
• Found only in producers (organisms containing chlorophyll)
• Use energy from sunlight to make own food (glucose)
• Energy from sun stored in the chemical bonds of sugars
• Surrounded by DOUBLE membrane
• Outer membrane smooth
• Inner membrane modified into sacs called thylakoids
• Thylakoids in stacks called grana & interconnected
• Stroma – gel like material surrounding thylakoids

The Cells’ Need to Divide

Cell Division
– About two trillion cells are produced by the adult human body each day, and around 25 million new cells are
produced per second.
– Millions of successful cell divisions have occurred until this very time that you are listening to the teacher.
– also known as cell reproduction, is actually linked to the cell theory which states that all living things are
composed of cells, that came from preexisting cells.
– Cell division allows organisms to reproduce asexually, grow, and repair worn-out or damaged tissues (cell
replacement).

Growth and Development

– Cell division is associated with growth and development. Even humans are products of numerous cellular
divisions, as life begins with only single cell from the fusion of the parents’ sex cells.
– In about nine months, that single cell becomes trillions of cells due to the numerous cell division that occur
during embryotic development.

Cell Replacement
– Occurs when old cells in the body die and new cells form.
– At this moment, thousands of your cells are produced, such as your red blood cells, intestinal cells, and skin
cells.
– Cells in your epidermis are continuously being replaced because dead skin cells are sloughed off in activities
like washing your hand.
– Cell division occurs in the red bone marrow of your bones such as in the ribs, breastbone, vertebrate, and hips
to continuously make new red blood cells to replace the dying ones. Wound healing also involves growth of
new cells out of cell division.
– If your skin is injured with a cut, cellular repair will also happen with the production of new cells on the site
of injury.

Production of Red Blood Cells

– Bone marrow

Reproduction
– Reproduction is a common process among life forms, to make a new organisms from one or two parent
organisms.
– It happens either via Sexual or Asexual Reproduction.
– Sexual Reproduction involves two specialized cells called gametes, coming from the parents that will result to
a unique offspring.
– Asexual Reproduction is the production of offspring from a single parent without the involvement of gametes.
The offspring is genetically identical with each other and to the single parent.

Cell Division in Zygotes (Sexual Reproduction)

Asexual Reproduction
– For most bacteria and other unicellular organisms, reproduction involves simple cell starts to divide, its DNA
circle makes a copy of itself.
– After it is copied, the cell must reach its appropriate size, then it splits into two equal halves.
 – During the cell division, the cell is gradually constricted at its center, like a tightening belt around an
elongated balloon. Eventually, the cell pinches apart, splits into two, then a new cell wall forms between two
daughter cells. This process is known as binary fission.`
– The faster the rate of cell division is attributed to its cell structure lacking a nucleus. Since they have less
DNA in the form of a single circular chromosome and no spindle fibers, then it makes it faster for the
bacterium to divide.
– Cell division is important for reproduction, while multicellular organisms use it for growth, development, and
repair.
– Examining the nucleus, it will reveal the genetic material organized in chromosomes.

Chromosomes
– When you were born, you received a complete set of DNA from your parents, which carries the genetic
information you have inherited and makes your body function normally throughout your life.
– DNA is a double-stranded molecule, is tightly coiled in an organized structure called chromosomes.
– A chromosome is simply a long, continuous thread of DNA wounded together by DNA-associated proteins,
referred to as histones.
– Each of your body cells consists of 46 chromosomes or 23 pairs. If stretched end to end, it would be around 10
feet long. (304.8 cm)
– Before the onset of cell division, DNA is loosely organized like scattered spaghetti on a plate.
– During a cell division, on the other hand, the chromosomes become tightly condensed. This step is required,
so the chromosomes will not be entangled during cell division; that is why duplicated chromosomes must
condense first, before they divide into two daughter cells.
– If this is not done, some cells may receive one copy instead of two copies or other cells may receive none at
all.
– As mentioned earlier, before cell division takes place, the DNA and proteins are loose like a spaghetti. These
complex set of macromolecules that contain loose DNA, proteins, and RNA is called chromatin.
– Chromatin is responsible for packaging the DNA efficiently into smaller volume so that it fits the nucleus of
a cell to protect the DNA structure and sequence, to prevent DNA damage, to control gene expression and
DNA replication, and to reinforce the DNA molecule to allow mitosis and meiosis.
– As the cells progresses in the cell division, chromatin further condenses, coiling more and more tightly around
the proteins and eventually forming small, thick rods.
– Once the chromosomes has been copied, the chromosomes now appears to be similar to a letter X in which the
left and the right halves are identical.
– Chromatids refers to each strand of the duplicated chromosomes. Together they are called sister chromatids,
which are held together by centromere, a region of condensed pinched chromosomes.
– Located at the centromere is a group of proteins called kinetochore, which is attached to the long spindle
fibers during cell division.
– At the ends of the DNA molecule are structures referred as telomeres that contains repeated nucleotides,
which contain genetic information that do not translate traits.
– The role of nucleotides is to prevent the ends of chromosomes from accidentally attaching to one another and
prevent the loss of genes.
– Since a short section of the nucleotide is lost every time a new DNA is copied, then it is better to lose these
nucleotide from telomeres rather than from the genes themselves.

Telomeres, end caps that protect the chromosome

The Cell Cycle

Why do cells divide instead of just growing bigger?

• The larger the cell, the more demands it places on DNA
• Small cells, the DNA can meet the needs of the cell
• As cell grows, the DNA cannot meet the needs of the cell – does not make extra copies of
DNA to meet needs

Cell Size
• The larger the cell, the more difficult it is to transport nutrients and waste across the cell membrane. The cell
membrane’s inefficiency increases
• Exchange rate of materials is dependent on the surface area
• Understanding the relationship between surface area to volume is the key to understanding why cells must
divide as they grow
The Mechanism of Cell Division: Mitosis

The Interphase (I)

• There are two main phases in the cell cycle: The Interphase and the mitotic phase.
• Interphase is the period during the cell cycle of cell’s growth and development
• Interphase is followed by a shorter period of the cell cycle known as the mitotic phase where cells starts to
reproduce
• Gap1 (G1) – First growth phase. Metabolic activity proceeds at a normal rate. Duration highly variable.
Synthesis of enzymes related to DNA replication.
• Synthesis (S) – DNA replication.
- All chromosomes replicated.
- Chromosomes consist of 2 sister chromatids in chromatin form.
- Histones produced.
• Gap 2 (G2)
- During the second gap phase, or G2 phase, the cell grows more, makes proteins and organelles, and begins to
reorganize its contents in preparation for mitosis.
- G2 phase ends when mitosis begins.

Organelle Replication
• During cell division the organelles in a cell are distributed between the two new cells.
• Before a cell divides, it makes a copy of each organelle.
• This enables the two new cells to function properly.
• Some organelles, such as the energy-processing mitochondria and chloroplasts, have their own DNA
• A cell makes these materials using the information contained in the DNA inside the nucleus.
• Organelles are copied during the stage of interphase.

The Cell Cycle

Mitosis
• Process that divides cell nucleus to produce two new nuclei each with a complete set of chromosomes
• Continuous process
• Four phases (PMAT)
• Prophase
• Metaphase
• Anaphase
• Telophase

Prophase
1. chromosomes visible (sister chromatids)
2. centrioles migrate to the poles (only in animals)
3. nuclear membrane disappears
4. spindle forms

Metaphase
1. chromosomes line up on the equator of the cell
2. spindles attach to centromeres
Anaphase
1. sister chromatids separate
2. centromeres divide
3. sister chromatids move to opposite poles

Telophase
1. chromosomes uncoil now chromatin
2. nuclear membranes reform
3. spindle disappears

Cytokinesis
- Occurs at end of Mitosis
- division of the cytoplasm to form 2 new daughter cells
- organelles are divided
- Daughter cells are genetically identical

Regulation of The Cell Cycle

• Unlike the life of organisms, which is a straight progression from birth to death, the life of a cell takes place in
a cyclical pattern. Each cell is produced as part of its parent cell.
• When a daughter cell divides, it turns into two new cells, which would lead to the assumption that each cell is
capable of being immortal as long as its descendants can continue to divide.
• However, all cells in the body only live as long as the organism lives. Some cells do live longer than others,
but eventually all cells die when their vital functions cease.
• Most cells in the body exist in the state of interphase, the non-dividing stage of the cell life cycle. When this
stage ends, cells move into the dividing part of their lives called mitosis.

External Factors
• External factors come from outside the cell that are in the form of messages from nearby cells or from parts of
the organism’s body
• Contact Inhibition – Happens when a cell touches another cell, it stops dividing.
• Anchorage dependent – Happens when cells only grow if surface is available and stops dividing when
detached from the surface.

Internal Factors
• It is essential that the daughter cells are exact duplicates of the parent cell. Mistakes in the duplication or
distribution of the chromosomes lead to mutations that may be passed forward to every new cell produced
from an abnormal cell.
• To prevent a compromised cell from continuing to divide, internal control mechanisms operate at three main
cell cycle checkpoints. A checkpoint is one of several points in the eukaryotic cell cycle at which the
progression of a cell to the next stage in the cycle can be halted until conditions are favorable (e.g. the DNA is
repaired). These checkpoints occur near the end of G1, at the G2/M transition, and during metaphase.
• The most well-studied Internal Factors in the Eukaryotic Cell cycle are kinases and cyclins.
• Kinase – an enzyme that transfers a phosphate group from one molecule to the target molecule.
• Cyclins – Activates kinases that help control cell cycle. Cyclins are rapidly destroyed at certain points in the
cell cycle to allow cells to progress from g1 stage to M stage

G1 stage checkpoints
• The G1 checkpoint determines whether all conditions are favorable for cell division to proceed. The G1
checkpoint, also called the restriction point (in yeast), is a point at which the cell irreversibly commits to the
cell division process.
• External influences, such as growth factors, play a large role in carrying the cell past the G1 checkpoint. The
cell will only pass the checkpoint if it is an appropriate size and has adequate energy reserves. At this point,
the cell also checks for DNA damage.
• A cell that does not meet all the requirements will not progress to the S phase.

G2 Stage Checkpoint
• The G2 checkpoint bars entry into the mitotic phase if certain conditions are not met.
• As with the G1 checkpoint, cell size and protein reserves are assessed.
 •
However, the most important role of the G2 checkpoint is to ensure that all of the chromosomes have been
accurately replicated without mistakes or damage.
• If the checkpoint mechanisms detect problems with the DNA, the cell cycle is halted and the cell attempts to
either complete DNA replication or repair the damaged DNA.
• If the DNA has been correctly replicated, cyclin dependent kinases (CDKs) signal the beginning of mitotic
cell division.
Apoptosis
• A form of cell death in which a programmed sequence of events leads to the elimination of cells without
releasing harmful substances into the surrounding area.
• Apoptosis plays a crucial role in developing and maintaining the health of the body by eliminating old cells,
unnecessary cells, and unhealthy cells.
• The human body replaces perhaps one million cells per second. Too little or too much apoptosis can play a
role in many diseases.
• When apoptosis does not work correctly, cells that should be eliminated may persist and become immortal.
• for example, in cancer and leukemia. When apoptosis works overly well, it kills too many cells and inflicts
grave tissue damage. This is the case in strokes and neurodegenerative disorders such as Alzheimer's,
Huntington's, and Parkinson's diseases.
• Also known as programmed cell death and cell suicide.

Cancer
• A group of diseases that involve irregular growth and reproduction of cells
• Cancer occurs when genes involved in the cycle, specifically with check points are altered (growth factors)
• Transformation – single cell converts to a cancer cell
• Benign Tumor – a group of abnormal cells that does not invade other body systems- not considered cancerous
• Metastasis – when cancerous cells break off the original tumor and travel to other parts of the body
• Malignant Tumor – a tumor that invades a body system by traveling via the bloodstream or the lymphatic
system
• Cancer causes death because the cells take over the function of organs
• Cancer arises due to damage to genes (90%) or inheritance (10%)

Cancer and Cell Growth

• Cancer is essentially a failure of cell division control
• unrestrained, uncontrolled cell growth
• What control is lost?
• lose checkpoint stops
• gene p53 plays a key role in G1/S restriction point
• p53 protein halts cell division if it detects damaged DNA
• options:
• stimulates repair enzymes to fix DNA
• forces cell into Apoptosis
• keeps cell in G1 arrest
• causes apoptosis of damaged cell
• ALL cancers have to shut down p53 activity

p53
- Master Regulator Gene