3.3 Components of Cells

7/29/2019 3.3 Components of Cells

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Lesson Objective: Describe the structure, function

and location of cytoplasm.

TOPIC 2.0: CELL STRUCTURE AND FUNCTIONS

Cytoplasm is the entire region between the nucleus & theplasma membrane.

It consist ofcytosol & organelles suspended in it.

Cytosol contains various component:

About 90% water & solutes such as sugars, amino acids,enzymes, fatty acids, nucleotides, ATP & dissolved gases.

Large molecules such as proteins which form colloids

Microfilaments & microtubules which form thecytoskeleton, providing support to the cell & are involved

in cell mortality.Organelles are structures in cell which are suspended inthe cytosol and that carry out specialised function e.g.nucleus, mitochondria and chloroplast.

COMPONENTS OF CELLS


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and location of cytoplasm.


Cytoplasm is the entire region between the nucleus & theplasma membrane.

It consist ofcytosol & organelles suspended in it.

Cytosol contains various component:

About 90% water & solutes such as sugars, amino acids,enzymes, fatty acids, nucleotides, ATP & dissolved gases.

Large molecules such as proteins which form colloids

Microfilaments & microtubules which form thecytoskeleton, providing support to the cell & are involved

in cell mortality.Organelles are structures in cell which are suspended inthe cytosol and that carry out specialised function e.g.nucleus, mitochondria and chloroplast.

CYTOPLASM.


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Lesson Objective: Describe the structure and

function of organelles.


This is one of the specialize structures in the

cell that carry out specific functions, such as

the mitochondria, Golgi apparatus, ribosomes;

many organelles are membrane-bounded.

The membranes that surround membrane-

bounded organelles & the plasma membrane

have the same basic structure.

ORGANELLES


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and location of nucleus.


Nucleus is the most prominent organelle in the cell.

It is usually spherical or oval in shape & averages 5m indiameter.

The nuclear envelope consists of 2 layers of membranes that

separate the nuclear contents from the surroundingcytoplasm.

The spaces between the outer membrane & the innermembrane is known as perinucleus.

The nuclear envelope is perforated by numerous pores.Nuclear pores regulate the passage ofmaterials betweennucleoplasm & cytoplasm.

i. NUCLEUS


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Most of the cells DNA is located inside the nucleus.

DNA is associated with histone proteins, forming acomplex known chromatin.

In dividing cells, the chromatin condenses &

becomes visible, called chromosomes.Most nuclei have one or more compact structurescalled nucleoli (sing.,nucleolus).

A nucleolus is notmembrane-bounded.

Here a special type of RNA called ribosomal RNA issynthesized.


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TOPIC 2.0: CELLSTRUCTURE AND FUNCTIONS


7/39TOPIC 2.0: CELL STRUCTURE AND FUNCTIONS



Functions of nucleusNucleus is considered as the controlling centre of the cell.Nucleus contains the genetic information necessary for

reproduction, development and metabolism of theorganism as a whole.

Nucleus maintains the cell by directing the synthesis ofstructural proteins.

Nucleus regulates the metabolic processes in the cell bydirecting the synthesis of functional proteins such asenzymes.

Nucleus distributes the genetic material equally through theprocess of replication.

Nucleus is involved in the formation of ribosomes.



The Endomembrane System in Eukaryotic CellsAll eukaryotic cells have within them a functionally interrelated membrane

system, the endomembrane system consisting of the nuclear envelope, ER

and Golgi apparatus, vesicles and other organelles derived from them, and

the plasma membrane.

Many materials are moved around the cell by the endomembrane system,

including some proteins.


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and location of ER.


The ER is a membranous system which iscontinuous with the outer membrane &scattered extensively in the cell.

There are 2 distinct types of ER:1. Rough Endoplasmic Reticulum (RER)

2. Smooth Endoplasmic Reticulum (SER)

Although these regions have differentfunctions, the membranes are connected andtheir internal spaces are continuous.

ENDOPLASMIC RETICULUM (ER)



The RER consists of an interconnected system of

membrane-bounded flattened sacs called sisternae.

It is continuous with the outer membrane of thenucleus & has many ribosome on the outer surface

of its membrane.

RER is abundant in cells which are rapidly growing or

secretory cells. Eg: pancreatic cells.

Rough Endoplasmic Reticulum (RER)



It provides intracellular transportation of materialsinside the cell. eg. polypeptide chain synthesized onthe surface of ribosomes will then enter thecisternae of RER .

The protein will then be modified to formglycoprotein by addition of short polysaccharidechain before the glycoprotein is packed in transportvesicle.

Transport vesicle containing modified protein are

budded off from RER and are transported to Golgiapparatus. It forms an internal supporting framework for the

cell, called cytoskeleton.

Functions of RER



SER is more tubular & does not have

ribosomes bound to it, so its outer membrane

surfaces appear smooth.

SER is abundant in cells involved in lipid &

steroid hormone synthesis, eg. cells in the

testes & ovaries or cells involved in

detoxification, eg. liver cells.

Smooth Endoplasmic Reticulum (SER)



The SER is the site of lipid synthesis (triglycerides,phospholipids,cholesterol & steroid hormone) & themetabolism of carbohydrate.eg. SER in liver cells.

Enzymes of the SER in liver cells are involved in

detoxification. eg. drugs & alcohol.

The SER becomes modified to form sarcoplasmicreticulum surrounding the muscle microfibril. It stores orrelease calcium ions for muscle contraction.

The ER divides the cytoplasm into more compartments &increase surface area for chemical reactions to takeplace.

Functions of SER



SER RER

Tubular in shape and hassmooth appearance

A system of flattened

membrane bounded sac and

has granular or rough

appearance due to presence

of ribosome.

Site of phospholipid and fattyacid metabolism.

Site of protein synthesis.

Detoxify harmful chemicals Provides intercellulartransportation .

Involved in transport ofprotein to golgi apparatus.


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and location of Golgi body.


First described in 1898 by the Italian microscopist

Camillo Golgi.

Golgi apparatus consists of a stack of flattened,

membrane-bounded sacs called cisternae.However, unlike ER the internal spaces of Golgi

complex & the membranes are not continuous.

Each stack contains about 4-7 sisternae.Each Golgi stack has three areas referred to as cis &

trans faces with a medial region between.

iii.GOLGI APPARATUS/GOLGI BODY



Typically, the cis face is located nearest the nucleus &

functions to receive materials from transport vesiclesfrom the ER.

The trans face, nearest to the plasma membrane,packages molecules in vesicles & transports them

out of the Golgi.

The Golgi apparatus is continuously being formed atthe cis-end to replace the vesicles whish bud off atthe trans-end.

Golgi apparatus is abundant in secretory cells & cellsrapidly dividing e.g. Pancreatic cells, goblet cells, cellsin testes & ovaries.


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TOPIC 2.0: CELLS STRUCTURE AND FUNCTIONS


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The Golgi apparatus functions principally to process,sort, & modify proteins.

The glycoproteins are synthesize in the RER & later inthe Golgi.

The glycoproteins are transported from the RER tothe cis face of the Golgi apparatus in a smalltransport vesicles formed from the ER membrane.

Products of the ER are usually modified during their

transit from the cis face to the trans face of theGolgi.

Functions of Golgi Apparatus.


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For e.g. various Golgi enzymes modify the

oligosaccharide portions of glycoproteins.Oligosaccharides are first added to proteins in theRER.

The Golgi removes some sugar monomers &

substitutes others, producing a large variety ofoligosaccharides.

Glycoproteins are packaged in secretory vesicles inthe trans region.

These vesicles pinch off from the Golgi membrane &transport their contents to a specific destination.


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Vesicles transporting products for export from the

cell fuse with the plasma membrane.The vesicles becomes part of the plasma membrane

& the glycoproteins are secreted from the cells.

Other vesicles may store glycoproteins for secretion

at a later time.

In animal cells, the Golgi apparatus also

manufactures lysosomes.

In plants cells, the Golgi secretes polysaccharides forthe formation of cell plates & cell walls.


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and location of ribosomes.


Ribosomes are small, dense granules & made

of ribosomal RNA (rRNA) & protein.

Ribosome is composed of two subunits: a

large subunit & a small subunit.

v. RIBOSOMES


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and location of ribosomes.


Ribosome consists of 50% ribosomal RNA and 50% protein

Composition of ribosome


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Ribosomes are found attached to the RER or

occur freely within the cytoplasm.

Ribosomes can occur singly or group together

to form polysomes.

Cells that have high rates of proteins synthesishave a particularly large number of ribosomes.

E.g. a human pancreas cells.


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Site of proteins synthesis.

- Most of the proteins made by free

ribosomes will function within the cytosol,eg.

are enzymes that catalyze the first step of

sugar break down.

- Bound ribosomes generally makes proteins

that are destined either for insertion into

membrane, for packaging within certainorganelles such as lysosomes, or for export

from the cells (secretion).

Functions of ribosomes


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Mitochondria are found in nearly all eukaryotic cells, includingthose of plants, animals, fungi & protists.

Mitochondria are about 1-10m long.

The mitochondrion is enclosed by two membranes; the outermembrane is smooth, but the inner membrane is convoluted,

with infoldings called cristae.Cristae greatly increase the surface area of the inner membrane,providing a surface for the chemical reactions.

The cristae bear numerous, minute, regularly spaced particlescalled stalked particles or oxysomes.

There may be between 100,000 to 1,000,000 stalk particles in asingle mitochondrion!

The stalk particle enclose enzymes that are involved in therelease of ATP molecules from the oxidation of glucose.

vi. MITOCHONDRION


and location of mitochondria


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Between the two membranes is the intermembrane

space.The inner membrane encloses a fluid-filled matrix. In

the matrix can be found a few circular strands of

DNA, 70S ribosomes & enzymes that used in the

Krebs cycle.

DNA in the mitochondria enables the mitochondria

to replicate during cell division.

Function of mitochondriaMitochondrion are the sites of cellular respiration,

the catabolic process that generates ATP.


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Chloroplasts are large plastids found in thephotosynthetic tissues of plant e.g. mesophyll cells &algae.

Chloroplasts are organelles that contain chlorophyll,

a green pigment that traps energy forphotosynthesis.

Chloroplasts also contain a variety of yellow &orange light-absorbing pigments known ascarotenoids.

Chloroplast are typically disc-shaped structures,measuring about 5 to 10m in lengths.

CHLOROPLASTS


and location of chloroplast.


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Chloroplast is bounded by adouble membrane.

The inner membrane encloses a

fluid-filled space called the stroma,which contains enzyme ( catalyselight-independent reactions),

circular DNA, ribosomes, starchgranules & lipid globules.

A series of interconnectingflattened membrane-boundedsacs, called the thylakoids, are

found in the stroma. Thylakoidmembranes may be stacked intogranum (plural, grana).


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Site of photosynthesis.

- The grana & thylakoid membrane provide large

surface areas for chlorophyll & accessory

pigments to be located to trap light energy &carry out production of ATP & NADPH.

- The stroma contains enzymes to carry out

light-independent reaction ( Calvin cycle ) &

the production of high energy organic

molecules e.g. sugar.

Functions of chloroplasts.


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and location of centrioles.


Centrioles are found in animal cells.

The centrioles are located outside thenucleus in a material of poorly definedstructure called the centrosome.

Centrioles are paired cylinders

(about 0.3-0.5 m long & 0.24m

diameter) & held at right angle to

each other.

Each cylinder consists of nine tripletsof microtubules in a 9+0

arrangement.

There are no microtubules in thecenter

They are generally absent in plantcells, except in motile plant cells.

vii. CENTRIOLES


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http://micro.magnet.fsu.edu/cells/animalcell.html


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TOPIC 2.1: STRUCTURE AND FUNCTIONS OF ORGANELLES

Centrioles act as organizers of spindle

fibers & are involved in the separation of

chromosomes or chromatids during cell

division.

In some cells, centrioles divide to

produce basal bodies from which flagella& cillia develop.

Functions of centrioles


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Cytoskeleton

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3.3 Components of Cells

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