BT6303 CELL BIOLOGY

UNIT – II

CELL DIVISION AND CONNECTION

3RD SEMESTERDEPARTMENT OF BIOTECHNOLOGYBY GNANASINGH ARPUTHADAS.D

Contents Cell ------------------------------------------------------- 3 DNA vs RNA ------------------------------------------ 4 Chromosomes ----------------------------------------- 5 Cell Cycle ----------------------------------------------- 6 Mitosis --------------------------------------------------- 9 Meiosis -------------------------------------------------- 18 Mitosis vs Meiosis ----------------------------------- 20 Crossing Over ----------------------------------------- 21 Cell Junction ------------------------------------------- 22 Gap Junction ------------------------------------------ 23 Tight Junction ----------------------------------------- 24 Desmosomes ------------------------------------------- 25 Hemidesmosomes ------------------------------------ 26 References ----------------------------------------------- 27

CELL Cell is the basic structural, functional and

biological unit of all known living organisms

Often called as building blocks of life.

DNA

Double stranded A=T, G= C Carries genetic

information in most of the organisms

Single stranded A=U, G=C Carries genetic

information in some viruses

Types: messenger RNA transfer RNA ribosomal RNA

RNA

CHROMOSOMES

• Condensed DNA.

• DNA that is preparing to undergo cellular division

• Can now be seen with a microscope.

CELL CYCLE

G0 Phase

Interphase (90% of cell cycle)

Gap 1 (G1) Synthetic phase (S) Gap 2 (G2)

Mitosis (10% of cell cycle)

G0 PHASE

Resting phase

Cell leaves the cell cycle and stops dividing

G0 phase is viewed as either an extended G1 phase, where the cell is neither dividing nor preparing to divide, or a distinct quiescent stage that occurs outside of the cell cycle.

Stages of Mitosis - IPMATC Interphase

• G-1: Maturation.

• S-Phase: DNA replicates - makes a duplicate copy of itself.

• G-2: Organelles replicate and final preparations for division.

MITOSIS

Division of the nucleus

Also called karyokinesis

Only occurs in eukaryotes

Has four stages

Doesn’t occur in some cells such as brain cells

Four Mitotic Stages

10

ProphaseMetaphaseAnaphaseTelophase

Stages of Mitosis - IPMATCProphase

• The chromatin condense to form visible chromosomes

• The nuclear envelope begins to dissolve

• The centrioles divide and begin to migrate to opposite sides of the cell

Stages of Mitosis - IPMATCMetaphase

• Centrioles have moved to opposite sides of the cell

• The spindle has formed

• Chromosomes are lined up in the middle of the cell across the equator

Stages of Mitosis - IPMATCAnaphase

• The centromeres split and the spindles pull the sister chromatids apart toward opposite sides of the cell

Stages of Mitosis - IPMATCTelophase

• The chromosomes move to opposite sides of the cell.

• The nuclear envelope begins to reform around each set of chromosomes at opposite sides of the cell.

Stages of Mitosis - IPMATCCytokinesis

• Division of the cytoplasm

• Begins to occur during telophase

• Different in plants and animal cells

Animal Mitosis

Plant Mitosis

MEIOSIS

Only occurs in sexually reproducing organisms

The goal of Meiosis is to produce gametes 2 cell divisions result in 4 daughter cells The chromosome number is halved Meiosis increases variability as no 2

gametes are the same Involves two successive divisions

Meiosis I Meiosis 2

MEIOSIS I vs MEIOSIS II

Mitosis vs Meiosis

Crossing over Crossing over consists of a mutual exchange of

equal quantity (segments) of chromosomal material between two non-sister chromatids.

CELL JUNCTION

GAP JUNCTION(COMMUNICATING JUNCTIONS)

Adjacent plasma membrane are closely opposed. intercellular space narrows upto

2-3 nm.

Gap junctions are made up of large protein units called CONNEXONS

Tight Junctions (Zonula Occludens)

"Zonula“ means band "occludens" = that

close off the space between the cells.

are the most apical of the junctions

Seal cells of an epithelial sheet to create a permeability barrier (MCQ)

Desmosomes“macula adherens”

This junctional type resembles a single "spot-weld" and does not form a belt around the cell

Cadherins: transmembrane proteins.

Bind intermediate filaments rather than actin filaments

Hemidesmosomes“Half-Desmosomes”

Adhere epithelial cells to the basal membrane

Integrins are the transmembrane proteins.

Anchor proteins link integrins to intermediate filaments

References

1. Alberts, Bruce, “Molecular Biology Of Cell”, 4th Edition, Garland Science, 2008.

2. Lodish, Harvey etal., “Molecular Cell Biology”, 6th Edition, W.H.Freeman, 2008.

3. Dr. Liz Williams, “The Journal Of Cell Biology”, Volume 194, No. 3, August 8,2011.

4. Kara Rogers, “The Cell”, 1st Edition, Britannica, 2011.

THANKYOU

Submitted toDr.P.Dhasarathan Ph.D,

Senior Assistant Professor,Department Of BioTechnology,

PITAM.