This document summarizes various cell structures and their functions. It discusses ribosomes, which synthesize proteins, and polyribosomes, the components of which include DNA, mRNA, tRNA and rRNA. It describes the endoplasmic reticulum, where proteins are synthesized and modified, and the Golgi apparatus, where proteins and carbohydrates are further processed and sorted. Lysosomes aid digestion, while peroxisomes contain oxidative enzymes and aid in protein degradation. Mitochondria perform oxidative phosphorylation and lipid synthesis. The cytoskeleton, comprising actin filaments, intermediate filaments and microtubules, maintains cell shape and enables intracellular movement.

1. CELL STRUCTURE
Prof. Redem C. Deligero, MATMRS;MSES

2. RIBOSOMES
1. Small Subunit

Sedimentation Value
(40S & 33 Proteins)

P-site - for binding
peptidyl transfer
ribonucleic acid
(tRNA)

A-site - for binding
aminoacyl tRNA
2. Large Subunit

Sedimentation Value
(60S & 49 Proteins)

3. Polyribosomes

Responsible for protien synthesis.

Proteins for package is made in the RER
surface.

Proteins for cytosol are made within the cytosol.
Components of Polyribsome:
1. DNA
2. mRNA
3. tRNA
4. rRNA

4. PROTEIN SYNTHESIS

5. Synthesis of Cytosolic Proteins
1. P-site of of the ribosomal subunit recognize the
iniator tRNA with AUG codon.
2. Large ribosomal subunit binds to small subunit &
moves mRNA in 5'-3' direction.
3. tRNA binds to A site.
4. Amino acids in A site and P site form peptide bond
catalyze by Peptidyl Transferase.
5. Deaminted tRNA leaves P-site and tRNA with two
amino acids moves to the A-site.
6. When A-site of small ribosomal subunit reach the
stop codon (UAG, UAA, & UGA) release factor
binds the A site.
7. tRNA release from P-site, release factor dettached
from A-site, small & large ribosomal unit leaves
MRNA

6. ENDOPLASMIC RETICULUM

System of interconnected
tubules & vesicles

Cistern - the vesicles
lumen.
Metabolic process:

Protein synthesis &
modification

Lipid & Steroid synthesis

Detoxification of toxic
compounds

Membrane manufacture.

7. Synthesis of Protein in RER

Identification of proteins for delivery outside the
cell by signal peptide.

Signal Recognition Particles (protein complex)
recogize signal peptide.

Small subunit ribsome halts translation as SRP-
signal peptide complex occupy the P-site.

Polysome migrateto RER.

SRP receptor protein (docking protein) in RER
membrane contacts SRP& ribosome receptor
protein contacts large subunit ribosome.

Polysome attach to the cytosolic surface of the
RER.

8. GOLGI APPARATUS

Synthesis of
carbohydrates.

Modification and sorting
of proteins from RER.

Made up of series of
flattened, slightly curved
membrane bound
cisternae.

Each cisterna is dilated
peripherally and rimmed
with vesicle that either
fuse or bud-off from that
particular compartment.

9. Golgi Additional Compartment
1. Endoplasmic Reticulum/Golgi
Intermediate Compartment (ERGIC).

Between RER & cis-face.

Derived from fusion of transfer vesicle.
2. trans Golgi Network (TGN)

Located at the distal side of G.A.

10. Golgi & RER - Associated Vesicles

Vesicle carrying protein bud-off facilitated
by proteinaceous coat on the cytosolic
aspect of the organelle.
1. COP I
2. COP II
3. Clathrin

11. LYSOSOMES

Have an acid pH &
hydrolytic enzymes.

A specialized organelle
for digestion of substance
from the late endosomes.

Diameter is 0.3 - 0.8 µm.

Acid hydrolyses present:

Sulfatases

Proteases

Nucleases

Lipases

Glycosideses

12. LYSOSOMAL ACTIVITY

13. ENDOSOMES

Also involved in ingestion,
sequestering &
degradation of substance
internalized from
extracellular space.

Has two compartments:

Early endosomes - at the
cell periphery

Late endosomes - deeper
into cytoplasm.

14. PEROXISOME

Self replicative with
oxidative enzymes.

Maintainance of protein
population.

Responsible for
proteolysis.

Aided by the following
enzymes:

Ubiquitine-activating
enzymes

Ubiquitine-conjugation
enzymes

Ubiquitine ligases

15. BETA-OXIDATION

16. MITOCHONDRIA

Perform oxidative
phosphorylation.

Involved in lipid
synthesis.
Component Structure:

Outer Membrane

Inner Membrane -
Folds within is called
cristae.

Intermembrane Space -
Between the inner &
outer membrane.

Matrix Space - Large
space within the inner
membrane.

17. CYTOSKELETON

Protein filaments
responsible for
maintenance of cellular
morphology.

Responsible for
intracellular movement.
Types of
Cytoskeleton:

Thin Filaments (Actin)

Intermediate Filaments

Microtubules

18. Actin Filaments

Responsible for
intracellular movement.

15 % in non-muscle cells.

It has G-actin - 2 chains
of globular subunits
coiled around each other
forming filaments.

It has a + end - fast
growing end & - end; a
slower growing end.

19. Intermediate Filaments

Maintain the 3-D
framework of the cell.

Anchor the nucleus in
place.

Provide connection
between cell membrane
and cytoskeleton.

Help nuclear envelope
reorganization
subsequent to mitosis.

20. Microtubule

Long, straight, hollow
cylindrical structure.

Provide cell rigidity.

Establish intracellular
compartments.

Provide ciliary and
flagellated movement.