DNA

DNA structure contains

1. Five carbon sugar deoxyribose

2. A phosphate group

3. Nitrogenous base

What are the 4 nitrogenous bases

Adenine

Thymine

Cytosine

Guanine

A + T

G+C

What is the shape of DNA

double helix

When does DNA replication occur

during S phase of interphase by unwinding and deprecating into two templates (strands)

Leading Strand

The new DNA strand that is built continuously in the 5 to 3 direction toward the replication fork

Lagging strand

The new DNA strand that is built in Okazaki fragments in the 5 to 3 away from the replication fork

Interphase and its 3 phases

Definition the phase where cells aren’t dividing

1. G1 phase

2. S Phase

3. G2 phase

G1 phase

Occurs after cell division has burned metabolic activity

S phase

The phase where DNA replication happens

G2 phase

the shortest phase where the cels prepare to divide

Mitosis Characteristics

Cell division in plant cells and animal cells

Creates 2 identical daughter cells

• Both will contain the same number of chromosomes (diploid = 2n)

Double stranded chromosome and single stranded

Single stranded is also known as a chromatid

Double stranded has sister chromatids

Mitosis-prophase

• chromatin begin to coil and condense making individual chromosomes

• The nuclear membrane breaks down and nuclelous disappears

• The spindle of microtubules begin to form and spindle fibres begin to extend

- in animal cells spindle fibres are created by centrioles which migrate to opposite ends of the cell to make the spindle apparatus. The fibres that radiate from the astral rays form the aster

Mitosis metaphase

Defined by the chromosome lining up on equtorial plane, with spindle fibres attached to their kinetoochores

• chromosomes line up in the middle

• Spindle fibres attach at kinetochores

• Sister chromatids still joined together

Kinetochere

Region on centromere where spindle fibres attaches

Mitosis- anaphase

Divides the centromere and attitude is the daughter chromosomes as they get pulled apart by the spindle fibres. They each end up on opposite sides

Mitosis telophase

prophase but in reverse, chromosomes return to chromatin state

New nucelar membranes nuceli appear

spindle spidered dissappears

Cytokinesis

occurs at the time as telophase

Divides the cytoplasm

• in plants it is done by the cell plate

• In animal cells it is done by the cleavage furrow which pinches the cells until 2 are formed

Meiosis characteristics

Interphase is the same as mitosis

Has two different cell divisions

Created 4 haploid cells

Gametes

Haploid means half the number of chromosomes present in a diploid cell

(Eg. Diploid= 46 Happloid =23)

They are genetically different

Meiosis- Prophase 1

differnces from mitosis (Generally the same)

• pairs like chromosomes (homologous pairs (tetrads) )

Crossing over occurs allowing for genetic variation

Meoisis- metaphase 1

Difference from mitosis:

• Homologus pairs line up in the middle of the cell with the spindle fibresattaced to the chromosomes

Independent assortment = Homologus pairs line up in random orientation, creating genetic variation

Meoisis - Anaphase 1

Difference from mitosis:

• there are no division of the centromeres

• Each chromosome (Half the tetrad goes to opposite pole)

• Sister chromatids do not seperate

Meiosis - telophase 1 ( and cytokinesis)

Homologus chromsones have reached opposite poles and the cell divides into two hapoloid daughter cells, each with half the orginal chromosome number

Meiosis 2

Similar process as mitosis

The second division of Meoisis, where sister chromatids seperate, producing four genetically different haploid cells, each with half the orginal chromosome number