cell cycle mr scutt. lesson objectives to know the three stages of the cell cycle. grade c to...

Keywords: Interphase; Nuclear Division; Cell Division; CancerKeywords: Interphase; Nuclear Division; Cell Division; Cancer

Cell CycleEukaryotic cells have a well- defined cell cycle of growth and division (mitosis). The length of the cycle varies (from minutes to hours, or , longer) ending with mitosis.

Each phase of the cycle involves specific activities, and varies in length from one organism to another.


Cell CycleThe cell cycle can be divided into stages:

G1 (“growth phase” 1) - Cells prepare for DNA replicationS (“synthesis”) - DNA replication occursG2 (“growth phase” 2)- Short gap before mitosisM Mitosis (relatively short)


Cell CycleAffected by availability of nutrients

Between each stage the cell “checks” to see if it is OK to proceed to the next stage.

“Proof-reading” enzymes check the copied chromosomes for mistakes (mutations) – the cell may kill itself (undergo “suicide”) if harmful mutations are – a process known as apoptosis.

Bacterial cells complete the cycle every 20 minutes. Muscle cells never complete the cycle – “terminal differentiation”

Uncontrolled and repeated cell division by mitosis results in cancer (tumours)


MITOSIS (M)

Nuclear division: Process by which a nucleus divides into two – each with an identical set of chromosomes – the nuclei are genetically identical

Cell division: Four phases – prophase, metaphase, anaphase, and telophase. Producing 2 cells (Mitosis) or 4 cells in Meiosis.

INTERPHASE

Period of cell growth:

G1 – Proteins from which cell organelles are synthesised are produced.

S – DNA replicated

G2 – Organelles grow and divide. Energy stores are increased.

CELLCYCLE

G1

S phase

G2

Mitosis (M)

Two daughter cells – genetically identical

Cell CycleLength of time – varies.

Mammalian cells – 24 hours (90% of which time is interphase).


G1 + S + G2 = INTERPHASE No apparent observable activity

G1 - First growth phase – longest phaseProtein synthesis – cell “grows”Most organelles producedVolume of cytoplasm increasesCell differentiation (switching on or off of genes)Length depends on internal and external factorsIf cell is not going to divide again it remains in this phaseDNA content = 20 (arbitary)

S - Replication phase DNA replication – this must occur if mitosis is to take placeThe cell enters this phase only if cell division is to followDNA content = 40

G2 - Second growth phase - shortShort gap before mitosis (cell division)Cytoskeleton of cell breaks down and the protein microtubule components begin to reassemble into spindle fibres – required for cell divisionDNA content = 40

The Cell Cycle – Comparing the Timings

CancerA group of diseases caused by a growth disorder of cells.

Caused by damaged genes which regulate mitosis and the cell cycle.

Therefore, leads to uncontrollable growth – tumours (a group of abnormal cells which develops and expands in size).


Cancer TreatmentHow can we stop it?

-Need to clock some part of the cell cycle.

How?

-Chemotherapy – using drugs:- Cisplatin – prevents DNA from replicating- Vinca Alkaloids – inhibits metaphase stage of mitosis by

interfering with spindle formation.

Problem:Affect normal cell division – e.g. hair producing cells.


What is the Cell Cycle?

SOME PAST PAPER QUESTIONS

Keywords: Chromosomes, Asexual reproduction, Mutation, Haploid, DiploidKeywords: Chromosomes, Asexual reproduction, Mutation, Haploid, Diploid

Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.


cell cycle mr scutt. lesson objectives to know the three stages of the cell cycle. grade c to...

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