Cell and Molecular Biology - PowerPoint Presentation

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Cell and Molecular Biology

Behrouz Mahmoudi

Cell organelles-2

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Golgi apparatus

2Slide3

Golgi apparatus (sometime called the Golgi body).

It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898

Golgi apparatus consists of sacs (with a single membrane) which are stacked like pancakes. The sacs or folds of the Golgi apparatus are called cisternae

The cisternae stack has five functional regions:

the

cis

-Golgi network

,

cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network

3Slide4

Cells synthesize a large number of different macromolecules. The Golgi apparatus is integral in modifying, sorting, and packaging these macromolecules for cell secretion

(exocytosis) or use within the cell

4Slide5

The Golgi processes proteins made by the endoplasmic reticulum (ER) before sending them out to the cell. Proteins enter the Golgi on the side facing the ER (

cis side), and exit on the opposite side of the stack, facing the plasma membrane of the cell (trans side).

Each cisterna

contains

different protein modification enzymes.

It is also involved in the transport of lipids around the cell, and the creation of

lysosomes.

Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers—proteins, nucleic acids, carbohydrates, and lipids.

Lysosomes are

the cell's waste disposal system

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What do these Enzymes within the cisternae do?

1- catalyze the addition or removal of sugars from cargo proteins (glycosylation): glycosaminoglycans(GAGs).

2- addition of sulfate groups (

tyrosin sulfation) like heavy chain of

immunoglobulinM

3-

addition of phosphate groups (phosphorylation). One molecule that is phosphorylated in the Golgi is

Apolipoprotein

, which forms a molecule known as VLDL that is a constituent of blood serum.

6Slide7

The Golgi plays an important role in the synthesis of proteoglycans, which are molecules present in the extracellular matrix of animals

. It is also a major site of carbohydrate synthesis.This includes the production of

long unbranched polysaccharides .

Enzymes in the Golgi

polymerize several

of these GAGs via a

xylose link

onto the core

protein.

glycosylation mainly refers in particular to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules

The majority of proteins synthesized in the rough ER undergo glycosylation.

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1- N-linked

glycans attached to a nitrogen of asparagine or arginine side-chains.

2- N-linked glycosylation requires participation of a special lipid called dolichol phosphate

.3- O-linked glycans attached to the

hydroxy

oxygen of serine, threonine, tyrosine,

hydroxylysine

, or

hydroxyproline

side-chains, or to oxygens on lipids such as ceramide.4- C-linked glycans, a rare form of glycosylation where a sugar is added to a carbon on a tryptophan side-chain.5- Glypiation, which is the addition of a GPI anchor that links proteins to lipids through glycan linkages.

8Slide9

The Cell Nucleus

The nucleus is a highly specialized organelle that serves as the

information processing

and administrative center of the cell.

has two major

functions;

1-

stores

the cell's

hereditary material or DNA2- coordinates the cell's activities, which include growth, intermediary metabolism

,

protein synthesis,

and

reproduction

(cell division)

The semifluid matrix found inside the nucleus is called

nucleoplasm

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Chromatin and chromosome

In the nucleus, the DNA double helix is packaged by special proteins (

histones

) to form a complex called chromatin. The chromatin undergoes

further condensation

to form the

chromosom

e. Chromosomes are condensed Chromatin Fibers

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The nucleolus

The nucleolus is a

membrane-less organelle

within the nucleus that manufactures ribosomes, the cell's protein-producing structures.

After a cell divides, a nucleolus is formed when chromosomes are brought together into

nucleolar

organizing regions.

During cell division,

the

nucleolus disappears11Slide12

Ribosomal RNA Genes

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The nuclear envelope

The nuclear envelope is a double-layered membrane that encloses the contents of the nucleus. The space between the layers is called the

perinuclear space and appears to connect

with the rough endoplasmic reticulum

The

inner surface

has a protein lining called the

nuclear lamina

, which

binds to chromatin and other nuclear components.

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nuclear pores

These pores regulate the passage of molecules between the nucleus and cytoplasm,

All transport between the nucleus and the cytoplasm passes through the nuclear pore complex (NPC)

The

nuclear pore

complex is made of

thirty different proteins

known as

nucleoporins

; there are about 500-1000 proteins in the NPC because the NPC has internal symmetry and each

nucleoporin

repeats many times

.

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