4.3 DNA replication and cell cycle

Replication Steps

1) double helix unwinds

2) DNA helicase open up a short segment of the helix at a time, exposing nitrogenous bases - the part that is open looks like two halves of a zipper being open called replication fork

3) molecules of enzyme DNA polymerase move along and read the exposed bases and then arrange matches between complementary nucleotides

Cell Cycle

A cell dividing into two daughters

Interphase: G1 first gap phase → S synthesis → G2 second gap phase → then enters into Mitotic phase prophase → metaphase → anaphase → telophase → cytokinesis

Interphase

G1 1st Gap Phase: interval between cell division and DNA replication. Cells synthesis proteins, grown, carries out tasks determined by the body

S Synthesis Phase: duplicates a copy of its centrioles and nuclear DNA, carries out replication, two identical sets of DNA molecules are available to be divided up

G2 2nd Gap Phase: interval between DNA replication and cell division, cell exhibits further growth, makes more organelles, finishes replication and synthesizes enzymes that control cell division

Mitotic Phase: prophase

Chromosomes shorten, thicken, and coil into compact rods and are easier to distribute to daughter cells than long, delicate chromatin of interphase.

46 chromosomes, each w/ 2 chromatids and 1 molecule of dna each.

The nuclear envelope disintegrates and releases chromosomes into cytosol, then the centrioles begin to grow spindle fibers that push centrioles apart as they grow.

Eventually they lie at each pole of the cell and they grow attached to the kinetochore at each side of the centromere.

They pull chromosomes back and forth until they line up in the middle of the cell

Mitotic Phase: metaphase

The chromosomes are lined up on cell equator, and move slightly - they need a signal to move each of them to split into two at the centromere

This forms the mitotic spindle, a lemon shaped area

Long microtubules reach out from the centrioles to the chromosomes and shorter microtubules form a star like aster that anchors the assembly of the inside to each end of cell wall

Mitotic Phase: Anaphase

Begins with an enzyme activating that cleaves the chromatids from each other at the centromere

Each chromatid is now a separate single stranded daughter chromosome

One daughter migrates to opposite polar sides of the cell, with the spindle fiber being destroyed as they do

Mitotic Phase: Telophase

The chromosomes cluster on each side of the cell, the rough ER produces new nuclear envelope around both

Chromosome begin to uncoil and return to thinly dispersed chromatin

Mitotic spindle breaks up and vanishes

The new nucleus forms nucleoli and it beginning to remake RNA for protein synthesis

Cytokenesis

Overlaps with telophase

Divides cytoplasm into two cells

Moto proteins myosin pull microfilaments of actin into web of the cytoskeleton

Creates a furrow and the cell pinches into two and interphase has begun