Cells can’t live forever. How do they keep tissues and bodies fresh?

Cell Growth and Cell Division

Licentious division - prostate cancer cells during division.

The Cell Cycle is the story of a cell’s life…

Video: Cell Division and the Cell Cycleby Frank Gregorio

https://www.youtube.com/watch?v=Q6ucKWIIFmg

Why do cells need to divide?

• Growth

• Development

• Repair

• Reproduction

Before a cell can divide, it has to have a “brain”

What is the brain of the cell?

What does it do?

If we wanted to create another you, we would first need the brain to direct your functions. What else would we need?

Let’s take a look at a cell’s genetic information first.

What is a chromosome?

chromatin

duplicatedchromosome

What is a chromosome?

chromatin

duplicatedchromosome

Coiled DNA = chromosome

Uncoiled DNA = chromatin

Each half of chromosome is one copy: chromatid

• CHROMATIN is coiled and tightly packed into structures called CHROMOSOMES.

• These coiled structures are only visible during MITOSIS (Cell Division).

• This explains why a copied chromosome has identical halves called CHROMATIDS that are connected at the CENTROMERE.

• During cell division, each half of a copied chromosome goes into a separate cell.

Chromosomes and the Cell Cycle

The Link Between DNA Replication and Chromosome Duplication

DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell

95% of the time, chromosomes are like this – referred to as chromatin

Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell.

A Replicated Chromosome

Centromere is constricted area on chromosome

Kinetochore is protein structure attached to centromere

Each half of chromosome is called a chromatid.

During their lives, cells grow, divide, perform their necessary functions, divide some more, and eventually die.

As they grow and divide, they go through an orderly sequence of steps called the Cell Cycle.

There are two main parts to the cell cycle: Interphase (where cells do their regular things and grow) and Mitosis (where the cells divide into two identical copies of themselves)

Resting Parent Cell

Two Daughter Cells

Daughter cells are genetically identical to parent cell

Important Facts about Interphase

• DNA is stretched out in long strands called chromatin.

• DNA needs to be stretched out to do its work, so that portions can be copied to make proteins

• All DNA is held in nucleus.

Cell Cycle has Four Phases

Interphase

• Longest phase of Cell Cycle

• Cells go about their normal business

• Cells also grow in size and copy their DNA

First Step of Interphase: G1

• Called G1 because it is first stage of cell growth

• Cells go about their normal business, depending on their job

• They make copies of organelles (e.g. mitochondria, ribosomes, golgi bodies, etc.)

• Called “S phase” because new DNA is synthesized.

• The DNA is copied to make two sets of identical DNA.

• One of these copies will end up in each daughter cell.

Second Step of Interphase: S

• Called G2 because it is second stage of cell growth

• Cells again go about their normal business.

• Cells keep growing

• Copied DNA is checked for errors.

Third Step of Interphase: G2

• The period when cell divides into two daughter cells

• Has several different stages that we’ll discuss tomorrow

Last Step of Cell Cycle: Mitosis

Review of Cell Cycle

• What are four main stages?

• What happens in G1 phase?

• What happens in S phase?

• What happens in G2 phase?

• What happens during mitosis?

• G1, S, G2, Mitosis

• Cell grows and makes more organelles

• DNA is copied

• Cell grows more and checks DNA copies

• Cell divides into two daughter cells

Clicker Quiz1. Which stage is longest stage of cell cycle?

2. In which stage is DNA copied?

3. In which phase do chromosomes separate into two daughter cells?