Unit 6 Biology

Cell cycle

2 phases

Interphase

G0

G1

S

G2

Mitotic

Mitosis

Cytokinesis

Hayflick limit

How many times can a cell divide?

as the cells divide, the telomeres(or caps on the end of the chromosomes) eventually shorten over time until they disappear.

with each division, some of the actual chromosome information will be lost,

the cell cannot functionally divide properly

A cell can replicate itself around 50 times.

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CDKs

Enzymes

always inside of the cell

not functional until a cyclin attaches to it.

Cyclins

Proteins

expressed for a short time

accumulate within a cell

. Once they get to a certain concentration in the cell, the cyclins bond to the CDKs.

CDK-cyclin complex binds to a protein

gives it a phosphate group.

Cyclin is destroyed

Cdk’s lie dormant

This means that whenever cyclin levels rise, mitosis occurs cyclin levels fall back down, and the cycle repeats.

G0

Resting phase

The cell is neither dividing nor preparing to divide

Some cells stay in this phase for their entire lifespan

Neurons are permanently in the G0 phase and never divide.

S

G1

Make proteins and organelles for DNA synthesis.

Get Bigger

Most growth

A complete copy of DNA is created

In nucleus

DNA synthesis

G2

Rapid cell growth

Protein synthesis

Cell prepares for mitosis

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Type of cell division

2 Daughter cells created

Equal amount of chromosomes

4 phases

Prophase

The spindle fibers form

the DNA condenses into sister chromatids or chromosomes

The nuclear membrane surrounding the DNA disintegrates

Metaphase

the chromosomes line up in the middle of the cell

the spindle fibers attach to a sister chromatid each

Anaphase

the microtubules containing the spindle fibers are moved apart

Chromatids are pulled away from each other to opposite sides of the cell

Telophase

The spindle fibers disintegrate

The DNA unwinds back into normal DNA

The nuclear membrane reforms around the DNA.

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Physical process of cell division

After mitosis

Dividing the cytoplasm

Two daughter cells

Occurring at the same time as telophase

Cancer

Disease

The body’s cells grow uncontrollably in a certain area

Spreads to other parts of the body

Can occur in the Cell cycle due to mutations

Oncogenes

These are altered forms of genes known as proto-oncogenes.

responsible for promoting cell growth.

When altered or mutated, they become oncogenes and then can promote tumor formation or growth.

Usually Acquired

Having a mutation in just one of the two copies of a particular proto-oncogene is enough to cause a change in cell growth and tumor formation.

Tumor suppressor genes

3 main functions

Growth arrest

Growth arrest is where the cell stops growing due to mutation/damage, due to crowding, or lack of food.

DNA Repair

DNA Repair is when p53 finds a mutation and reports it to other proteins so that they can come and repair a mutation in the DNA.

Apoptosis

apoptosis is activated when p53 finds irreparable DNA damage, and there is no other way to maintain function other than to self-destruct.

DNA repair genes

Both slow down the cell cycle to repair or suppress mutations in the DNA.

Can be acquired or inherited

Characteristics of cancer affected cells

They stimulate their growth

They ignore growth-inhibiting signals

They avoid death by apoptosis

They develop a blood supply: angiogenesis

The tumor sends out signals saying “Feed me”

Nearby blood vessels extend and attach to the tumor to supply it

provides a passageway for tumor cells to move

They leave their site of origin to invade other tissues: metastasis

They replicate continuously to expand their numbers

They evade or outrun the immune response

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Types of DNA

3 forms

Chromatin

DNA tightly condensed into coils

Makes up Chromosomes

condensed into chromosomes during the prophase of mitosis.

Chromosomes

Made of chromatids

Either one or two

Made of one before replication

Made of two after replication

During telophase of mitosis, the chromosomes unwind back into regular DNA.

Sister Chromatids.

V like structure

The pair is held together by a centromere