CELL STRUCTURE

Prof. Redem C. Deligero, MATMRS;MSES

RIBOSOMES1. 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)

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. DNA2. mRNA3. tRNA4. rRNA

PROTEIN SYNTHESIS

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

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.

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.

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.

Golgi Additional Compartment1. 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.

Golgi & RER - Associated Vesicles Vesicle carrying protein bud-off facilitated

by proteinaceous coat on the cytosolic aspect of the organelle.1. COP I2. COP II3. Clathrin

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

LYSOSOMAL ACTIVITY

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.

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

BETA-OXIDATION

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.

CYTOSKELETON

Protein filaments responsible for maintenance of cellular morphology.

Responsible for intracellular movement.

Types of Cytoskeleton:

Thin Filaments (Actin) Intermediate Filaments Microtubules

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.

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.

Microtubule Long, straight, hollow

cylindrical structure. Provide cell rigidity. Establish intracellular

compartments. Provide ciliary and

flagellated movement.