lecture 2 - cell and cell division

8/10/2019 Lecture 2 - Cell and Cell Division

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Cell & cell division

Dr.R.Arulmoli



Learning objectives

• Understand the cellular anatomy.

• Describe the structure and function of a cell

membrane.• Describe the organelles of typical cell and

their functions.

•

Outline the nucleus & its functions.



Cell: Introduction

• Cytology-study of cell.• Building blocks of human body.

• 1665 – Described by Robert Hooke.

•

Fundamental components of animal & planttissues.

• Formed by division of preexisting cells.

• Smallest units performing vital functions.

• Maintains homeostasis at cellular level & also attissue, organ, organs systems and organismlevels.



Cell : Types

Two primary types:

1.Prokaryotic cells-

• cells without true nucleus

eg. Bacteria• smaller in size than eukaryotic cells

2.Eukaryotic cells-

•cells with nucleus

eg. Animals, plants and fungi



Structural differences between Plant and Animal cells

PLANT CELLS ANIMAL CELLS

Cell walls almost presentNo cell walls present outside

the cell membrane

Plastids occur in cytoplasm No plastids are found

Lysosomes not usually

evident

Lysosomes present in

cytoplasm

Centrioles present only in

cells of lower plant formsCentrioles always present

Large vacuoles filled with

cell sap

Vacuoles, if present, are

small and contractile or

temporary vesicles



• Located between the cell membrane and nuclear

membrane.

• 2 sub-divisions:

1.Cytosol or intracellular fluid

dissolved nutrients, ions, soluble &

insoluble proteins, and

waste products

High conc of K+ ions, low Na+ ions

High conc of proteins

low conc of carbohydrates and aminoacids and lipids.

2. Organelles

Structures which perform specific functions.

Cytoplasm



1. Non-membranous organelles

Cytoskeleton

Micro villi

Cilia

RibosomeCentrioles

2. Membranous organelles

Endoplasmic reticulum

Smooth and Rough

Golgi apparatus

Lysosomes

Perioxisomes

Mitochondria

3. Nucleus

Cellular organelles



Membrane Lipids:Phospholipids,

Bilayered,

Hydrophobic

Membrane Proteins:Integral proteins – Transmembrane proteins, plenty

Peripheral proteins – inner or outer surface

Based on functions

Anchoring, Recognition proteins, Receptors,

Carriers, Channels

Membrane Carbohydrates:

Proteoglycans, Glycoproteins, Glycolipids.

Glycocalyx

Cell membrane or Plasma membrane



• Permeability:Impermeable

Permeable

Selectively permeable

• Energy requirement: Active permeability

Passive permeability

• Transport process:

DiffusionFiltration

Carrier-mediated transport

Vesicular transport

Membrane permeability




Helps in synthesis of carbohydrates, proteins and fats.

Helps in storage of proteins and Ca ions

Helps in transport of materials.

Helps in detoxification of materials.2 Types: Rough and Smooth ER.

Smooth ER:

No Ribosomes

Synthesizes phospholipids, cholesterol, Sex hormones

Stores and synthesizes triglycerides, Ca and glycogen

Rough ER:

Has Ribosomes

Synthesizes proteins, modification of proteins and transport

Membranous Organelles



Golgi apparatus

• Enzymes and hormones are modified andreleased through exocytosis

•

Transport vesicles, Secretory vesicles,Lysosomes.

• Renews and modifies the cell membranes

• Forms special enzymes for use in cytosol.



Lysosomes

• Helps in defence

• Cleaning up and recycling materials

with in the cell

• Primary & Secondary Lysosomes



Mitochondria

• Structure

outer and inner

membrane

Numerous folds – cristae(increases the surface

area of the matrix of the

mitochondria)

• Power house of a cell by

producing ATP• Requires O2 for its activity –

aerobic metabolism



Control centreStructure and function characters of a cell

Nuclear membrane surrounds it.

double layered, 2 layers separated by a perinuclear space

Connected to the rough ER at many places

Nuclear pores

Chemical communication occurs between the cytosol via poresThere is movement of ions, small molecules

DNA and proteins are big and cannot pass through

Has regulatory proteins that transport specific proteins and RNA

Nucleoplasm

Fluid content of the nucleus

Matrix: is a network of filaments which provide supporthas ions, enzymes, RNA & DNA nucleotide, RNA and DNA

Nucleoli

Synthesize RNA

Contains - proteins – histones, enzymes, RNA and DNA

Nucleus



Mitosis

G 1

G 0 S

G 2

Stable cells

(hepatocyte)

Restriction point Diploid labile cells

Permanent cell

(eg , neuron)

Interphase

Mitosis

G 1

G 0 S

G 2

Stable cells

(hepatocyte)

Restriction point Diploid labile cells

Permanent cell

(eg , neuron)

Interphase

Presynthetic phase

Premitotic phase

DNA synthesis

Cell cycle



CELL CYCLE



Cell division



Mitosis

• Mitosis is nuclear division plus cytokinesis,

and produces two identical daughter cells

during prophase, prometaphase, metaphase,anaphase, and telophase.

• Interphase is often included in discussions of

mitosis, but interphase is technically not part

of mitosis.



Interphase

• The cell is engaged inmetabolic activity and

prepare for mitosis.• Chromosomes are not

clearly visible in the



Prophase

• Chromatin in thenucleus begins to

condense and becomesvisible aschromosomes.

• The nucleolusdisappears.

•

Centrioles begin movingto opposite ends of thecell and fibers extendfrom the centromeresas mitotic spindle.



Metaphase

• Spindle fibers align thechromosomes along themiddle of the cell nucleus.This line is referred to as

the metaphase plate.• This organization helps to

ensure that in the nextphase, when thechromosomes are

separated, each newnucleus will receive onecopy of eachchromosome.



Anaphase

• The paired chromosomes

separate at the

kinetochores and move to

opposite sides of the cell.



Telophase

• Chromatids arrive atopposite poles of cell,and new membranesform around thedaughter nuclei.

• The chromosomesdisperse.

• The spindle fibersdisperse, andcytokinesis or thepartitioning of the cellmay also begin duringthis stage.



Cytokinesis

• In animal cells,

cytokinesis results

when a fiber ring

composed of a proteincalled actin around the

center of the cell

contracts pinching the

cell into two daughtercells, each with one

nucleus.



Meiosis

• Meiosis is the type of cell division bywhich germ cells (eggs and sperm) are

produced. Meiosis involves a reductionin the amount of genetic material.

• Meiosis comprises two successivenuclear divisions with only one round of

DNA replication.

• Four stages can be described for eachnuclear division.



Meiosis I

• In meiosis I, chromosomes in a diploid

cell resegregate, producing four haploid

daughter cells. It is this step in meiosisthat generates genetic diversity.



Meiosis I

• Prophase I • DNA replication precedesthe start of meiosis I.

• During prophase I,homologous chromosomes

pair and form synapses, astep unique to meiosis.

• The paired chromosomesare called bivalents, and theformation of chiasmatacaused by geneticrecombination becomesapparent.



Prometaphase I

• The nuclear membrane

disappears.

• One kinetochore forms

per chromosome and

the chromosomes

attached to spindle

fibers begin to move.



Metaphase I

• Bivalents, eachcomposed of twochromosomes (fourchromatids) align at themetaphase plate.

• The orientation israndom, with eitherparental homologue ona side. This means thatthere is a 50-50 chance

for the daughter cells toget either the mother'sor father's homologuefor each chromosome.



Anaphase I

• Chiasmata separate.

Chromosomes, each

with two chromatids,

move to separate poles.

• Each of the daughter

cells is now haploid (23

chromosomes), but

each chromosome hastwo chromatids.



Telophase I

• Nuclear envelopes

may reform, or the

cell may quickly startmeiosis II.



Cytokinesis

• Analogous to mitosis

where two complete

daughter cells form.



Meiosis II

• Second division of meiosis: Gamete

formation

• Prophase 2: DNA does not replicate.

• Metaphase 2: Chromosomes align at the

equatorial plate.

• Anaphase 2: Centromeres divide and sister

chromatids migrate separately to each pole.• Telophase 2: Cell division is complete. Four

haploid daughter cells are obtained.



Meiosis

• One parent cell produces four daughtercells. Daughter cells have half the

number of chromosomes found in theoriginal parent cell and with crossingover, are genetically different.

• Meiosis differs from mitosis primarily

because there are two cell divisions inmeiosis, resulting in cells with a haploidnumber of chromosomes.



Summary



Cell and its organelles

Plasma membrane


Ribosomes

Golgi complexLysome and Peroxisomes

Vacuoles

Mitochondria

CytoskeletonCilia and Flagella



• The nucleus is the control center of a cell through

genetic information stored in the nucleus.Genes are

made of the nucleic acid DNA. Hundreds of genes arelinked together as chromosomes (chromatin).

Genes can be switched on or off and are indirectly

responsible for making proteins which do the work of

the cell.

NUCLEUS


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