155 Anatomy

Cell Structure and Function

 The Cell

• The cell is the basic structural and functional unit of

the body
• Each cell is unique in some way but all cells have
similar characteristics which are:
A. The plasma Membrane
B. The cytoplasm
C.The nucleus
 Plasma Membrane
• The outer limit or wall of the cell is the plasma membrane and
also called cell membrane.

• Function of the plasma membrane:

1. Physical barrier: encloses the cell, separating cytoplasm from
extracellular fluid.
2. Selective permeability: allow certain materials to flow into and
out of a cell.
a. To maintain the difference in the composition of intracellular and
extracellular fluids
b. Na+ is higher in the extracellular fluid while K+ is higher in the
intracellular fluid.
3. Communication: The membrane also play a key role in
communication between the other cells.
4. Cell recognition: cell surface carbohydrates allow cells to
recognize each other (immune cell).
 Structure of Plasma Membrane

• Consists of phospholipids, cholesterol, carbohydrates

& proteins
 Structure of Plasma Membrane
• Phospholipid is the main substance (75%) that makes the
plasma membrane. It consists of two parts: polar hydrophilic
head and nonpolar hydrophobic tail. It forms a double layer of
lipids molecules described as a bilayer (bi means two).
• A few molecules move freely such as carbon dioxide, oxygen
and lipid-soluble materials.
 Structure of the Plasma Membrane
• Cholesterol, are located between the phospholipids.
Function to strength the membrane.
• Carbohydrates found only in the outer surface of the cell
membrane could be attached to lipids (glycolipids) or
attached to protein (glycoprotein). Function to help cells to
recognize each other and help the cells to stick together.
 Structure of the Plasma Membrane
• Proteins: are divided into transmembrane and peripheral
proteins.
– Transmembrane proteins extend into or across the entire
lipid bilayer among the fatty acid tails of the phospholipid
molecules.
– Peripheral proteins are found at the inner or outer surface
of the membrane.
 Function of Proteins in Cell Membrane
Type of Protein Function
Channels Pores in membrane that allow passage of specific
substances
Transporters Shuttle substances across membrane
Receptors Allow for attachment of substances to membrane; used for
cell-to-cell signaling
Enzymes Catalyze chemical reactions at membrane surface
Linkers Give structure to membrane and attach cells to other cells
Cell identity Glycoproteins unique to a person’s cells; important for
markers immunity; used for cell-to-cell recognition
Transport across the Plasma Membrane

• There are two types of transport:

1) Passive processes: movements of materials across the

cell membrane without the need of energy

Examples:

A. Diffusion
B. Facilitated Diffusion
C. Osmosis
Transport across the Plasma Membrane

2) Active processes: movements of materials across the cell

membrane that requires cellular energy

In active processes the cell uses energy to transport against

the concentration or the electrical gradient.
The cellular energy is used in the form of ATP (Adenosine
triphosphate).

Examples:
A. Active Transport
B. Endocytosis
C. Exocytosis
 Passive Transport
Type of Definition Examples Picture
Passive
Transport

Diffusion Movement of solutes through Lipid-

plasma membrane from high to soluable
low solutes concentrations materials
and gases

Facilitated Movement of solutes through Glucose

diffusion plasma membrane from high to and ions
low solutes concentrations
but using transporters or
channels

Osmosis Movement of water from high Water

water to low water
concentrations across plasma
membrane
 Active Processes
Type of Definition Examples Picture
Active
Processes

Active Movement of solutes through Na-K pump

transport plasma membrane from low to
high concentrations that requires
energy and transporters

Endocytosis Movement of bulk materials Bacteria

inside cells

Exocytosis Movement of materials outside Proteins

cells
 Nucleus
• Nucleus: spherical in shape and is the control center of the
cells; houses DNA; directs activities of the cell.
• Most cells have a single nucleus, although, some cells don’t
have nucleus such as Red blood cells.
• Other cells have more than one nucleus like the skeletal
muscles and osteoclast.

• Nucleolus: dense spherical (non-membrane-bounded) bodies,

composed of RNA and proteins located inside the nucleus
producing ribosomes

• Nuclear envelope: encloses the nucleus and its contents

• Nuclear pore: pore in nucleus; can allow substances (RNA) to

leave
 The Cytoplasm
• Material between nuclear membrane and plasma membrane =
viscous fluid containing organelles
– Cytosol
• Fluid portion of cytoplasm
• Consists of water and dissolved materials
– Organelles
• Specialized cell structures that perform different cell
functions
 Cell Organelles
• Cytoskeleton: consists of three types of rods which are
microfilaments, intermediate filaments and microtubules.
1. Microfilaments: thin filaments consists mainly of actin. Function in
cellular movements and muscle contractions.
2. Intermediate filaments: Resist pulling forces exerted on the cell.
3. Microtubules: cylindrical structure made of tubulin proteins.
Function to maintain cellular shape and distribution of cellular
organelles.
 Cell Organelles
Name Description Function
Endoplasmic Network of membranes extend Rough ER produces and
reticulum from nuclear envelop through processes proteins;
(ER) cytoplasm; Rough ER has Smooth ER synthesizes
ribosomes; Smooth ER lack lipids, in muscle stores
ribosomes calcium, in liver breakdown
glycogen to glucose
Ribosomes Small bodies either free in Synthesize proteins
cytoplasm or attached to rough
ER
Mitochondria Bean-shaped with internal Generate ATP through
folded membranes aerobic cellular respiration
so is called power house

Golgi Stack (layers) of membranous Sorting and packaging

apparatus sacs proteins for export outside
the cell
Endoplasmic Reticulum and Golgi Apparatus
 Cell Organelles
Name Description Function
Lysosomes Sacs contain digestive enzymes Digest damage cell, remove
waste and foreign materials
from the cell
Peroxisomes Sacs contain oxidative enzymes Destroy harmful substance
produced in metabolism
Centrosome Located near the nucleus and Form mitotic spindle to
contains pair of Centrioles (rod separate chromosomes
shaped bodies) surrounded by during cell division
microtubules
 Surface Structure
A- Cilia (move): are short hair-like projections which move the cell or
the fluids around the cell.
B- Microvilli: fingerlike cytoplasmic projection to increase surface area
for absorption
C- Flagellum: are long whip-like extension from the cell used to move
the cell, example tail of the sperm
 Cellular Adaptation

• Atrophy: decrease in the

cell size.
• Hypertrophy: increase in
the cell size without cell
division.
• Hyperplasia: increase in the
cell numbers due to increase
in the frequency of cell
division.
• Metaplasia: transformation
of one type of cell into
another.