Comparison Between Prokaryotic and Eukaryotic Cells

Property Prokaryotic Cells Eukaryotic Cells

Size Small Large (10-50 times)

Cell Wall Present Present in plant cells only

Photosynthetic Chlorophyll but not in Chlorophyll but not in

Apparatus chloroplast chloroplast

Membrane-bound No Yes
Organelles

Microtubules No Yes

Intermediate No Yes
Filaments

Exocytosis and No Yes

Endocytosis

Mode of Cell Cell Fission Mitosis and Meiosis

Division

Genetic Material Circular DNA DNA in form of chromosomes

Genetic DNA molecule complex with DNA complexed with proteins

Information relatively few proteins (notably histones) to form
chromosomes

Processing of Little Much

RNA

RIbosomes Small (70S): 3 RNA molecules Large (80S): 4 RNA molecules

and 55 proteins and 78 proteins

Prokaryotes (before kernel, or nucleus)

Strictly unicellular and include bacteria and archaebacteria.
Have no true nucleus and no membrane-bound organelles

Eukaryotes (true kernel, or nucleus)

Both unicellular and multicellular (plants and animals)
Have true nucleus and membrane-bound organelles, each of which performs a
specific function
 Membranous Organelles
Organelle Structure Function
 Double membrane (Nuclear Envelope) It controls all cellular activities including:
 Spherical or ovoid organelle 10-20m in diameter  Cell Division
 Membrane continuous with endoplasmic reticulum (perinuclear  Protein synthesis
Nucleus space is continuous with ER lumen)  Production of ribosomal DNA at the nucleolus
(double-bound)  Perforated with nuclear pores (50nm) approx 4000
 Contains nucleoplasm, a gel-like matrix that fills up the internal Protects DNA (hereditary/genetic material) from metabolically active cytoplasm via
portion of the nucleus compartmentalization
 Contains nucleolus, dense regions that contain large loops of DNA
Nuclear pores allow the movt of RNA out of the nucleus for protein synthesis
Membrane bound cisternae continuous with nucleus membrane Rough ER:
 Required for protein synthesis – folding proteins into their secondary/tertiary
Rough ER: comprises of extensive network membrane bound structures
flattened cisternae with ribosomes (bound ribosomes) attached to  Serves as an intracellular transport network between the various parts of the
their surfaces cytoplasm and between the cytoplasm and nucleus
 Serves for ribosomes to be embedded which synthesize proteins destined for
Endoplasmic Smooth ER: comprises of a system of interconnected tubules export
Reticulum
(double-bound) Smooth ER:
 Lipid synthesis and transport (eg phospholipids)
 Synthesis of steroids and reproductive hormones
 Metabolism of carbohydrates
 Detoxification of drugs and proteins
 Package certain proteins from rER in the cisternae for transport to other parts or
cell or exocytosis.
 Consists of flattened saucer like membrane-bound stacks called  Where modification and packaging of ER products occurs
cisternae  Multiple cisternae: allow for different modification processes to occur
 Cis face (outer convex face), new cisternae are constantly formed simultaneously
by the fusion of buds from rER and sER  Glycosylation: Synthesis of glycoproteins or glycolipids
 Trans face (inner concave face), the Golgi Apparatus breaks up to  Trimming: Excess monomers
Golgi Apparatus form vesicles called lysosomes and golgi vesicles  Secretion of proenzymes/modified proteins via Golgi Vesicles
(double-bound)  Proteins are packaged into transport vesicles at the sER which are pinched off
for transport to the cis face of GA
 Proteins are further modified as they move through the GA from the cis face to
trans face where they are packaged into transport vesicles or in the form of
lysosomes
 Lipid transport (replenish phospholipid bilayer at cell membrane)
Lysosomes  Spherical sacs of 0.2 to 0.5m in diameter  Enables the cell to breakdown the particles via phagocytosis
(single-bound)  Bound by single membrane  Autolysis: self-destruction of the cell by the release of lysosomal enzymes
 Contains hydrolytic enzymes such as proteases and lipases and within the cell
RNAase  Autophagy: Destruction of worn out organelles by fusing the organelles with
 Serve as storage vesicle to keep enzymes apart from the rest of primary lysosome to form a secondary lysosome
the cell, hence preventing it from destroying the cell  Digestion of materials taken into cell via Endocytosis
  Contents are slightly acidic (pH 5)  Enzymes from primary lysosomes are released to remodel the matrix of the cell.

Membranous Organelles
Organelle Structure Function
 Fluid-filled sac bounded by a single-membrane In Animals:
In Animals:  Serve to house and transport substances taken in via phagocytosis
 Small, mobile organelles that contains substances In Plants:
In Plants:  Storage of organic compounds and inorganic ions
 One large central vacuole:  Disposal sites for toxic metabolic byproducts
Vacuoles
Tonoplast (membrane); Cell Sap (matrix within the tonoplast)  Contains pigments
(single-bound)
 Plant protection
 Cell growth and elongation as water accumulates in the vacuole, plant cells can
therefore increase in size with minimal investment in cytoplasmic synthesis and
without sacrificing surface area to volume ratio, as cytoplasmic contents are
pushed to the periphery of the cell
 1.5 to 10m in length; .025 to 1.0m in width  High convoluted infoldings called cristae serves to increase surface area for the
 Double membrane bound structure with a smooth outer membrane various enzyme systems and proteins eg, stalked particles embedment, thus
that is permeable to small molecules of Mr<21000 and inner increase efficiency of mitochondrial reactions
selectively permeable membrane that is highly convoluted with  Site for catabolic respiratory activity within the cell – Kreb’s Cycle and oxidative
infoldings called cristae phosphorylation
Mitochondria
 Contains circular mitochondrial DNA (implies endosymbiosis with  Energy in the form of ATP is made available for cellular function
(double-bound)
ancient prokaryotes), ribosome’s, RNA  Lipid metabolism – fatty acids are broken down into acetyl-CoA in the matrix and
 Elementary particles are present on the inner membrane on the on the inner membrane of mitochondrion
side facing the matrix – they contain ATPase for Adenosine
Triphosphate (ATP) Synthesis

 Found in photosynthetic organisms  Sites of photosynthesis

 Double membrane encloses the intermembrane-space  Light-dependent reactions occur at the thylakoid membrane while the light-
 Inside the chloroplast is a system of flattened sacs called independent reactions occur in the stroma
Chloroplast thylakoid membrane which forms stacks called granum (pl. grana)
(double-bound)  Connecting the stacks of grana are sheet-like thylakoids called
intergranal lamellae
 Fluid surrounding the thylakoid membrane is the stroma, which
contains DNA, 70S ribosomes and enzymes

Non-Membranous Organelles
Organelle Structure Function
 Small (70S): 3 RNA Molecules and 55 Proteins  Protein synthesis.
Found in prokaryotes, mitochondria and chloroplasts  Bound ribosomes: synthesize proteins destined for export or targeted to various
Ribosomes  Large (80S): 4 RNA Molecules and 78 Proteins membrane-bound organelles
Found in eukaryotes as free ribosomes in the cytoplasm and  Free ribosomes: synthesize proteins for intracellular use
attached to the rER
Centrioles  Transverse Section: 9 triplets of microtubules fused together to  Organize spindle fibers during cell-division
give a rod-like structure  Anchorage for cilia and flagella
 Each centriole is positioned 90 to each other.