All cells arise from other cells

Within multicellular organisms do all cells retain the ability divide?

No

What do eukaryotic cells that do retain the ability to divide show?

A Cell cycle

Order of cell cycle?(3)

1. Interphase

2. Mitosis

3. Cytokinesis

Label the chromosome

• sister chromatids are joined together by a centromere

• This occurs in a diploid cell(a cell that has two compete sets of chromosomes)

What are the two types of cell divisions in eukaryotic cells?

• Mitosis

• Meiosis

Mitosis is apart of what cycle?

The cell cycle

What happens in mitosis?

A parent cell divided to create two genetically identical daughter cells

How do daughter cells get identical copies of DNA from the parent cell?

DNA replication- the parent cell copies its DNA before dividing

What is mitosis needed for?(2)

• growth

• Repair of damaged tissue

What is the four key stages of mitosis called?

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

What happens in prophase?(5)

• chromosomes condense and become visible

• Centrioles move to opposite poles (to make spindle fibers)

• Nucleolus disappears

• Nuclear envelope breaks down

• Spindle fibres form and attach to centromeres (the middle thing on chromosomes)

What happens in metaphase?

Spindle fibers pull chromosomes so they line up along the equator

What happens in anaphase?(2)

• centromeres divide, separating each pair of sister chromatids

• spindle fibres shorten and pull chromatids to opposite poles of the cell(now referred to as chromosomes again.

What happens in telophase?(4)

• chromosomes begin to lengthen (uncoil) In doing so disappear

• Separate nuclear nuclear envelope form around each group of chromosomes

• Spindle fibres disintegrate

• Cytoplasm divides to form two separate cells = CYTOKINESIS

Mitosis is a big/small part of the cell cycle.

Small

Most of the cell cycle is made up of which phase?- and does this happen before or after mitosis?

• Interphase

• Before

Interphase is a period of what?(2)

• growth

• DNA replication

Interphase is sub-divided into 3 stages which are?

1. G1 - (GAP PHASE 1)

2. S - (Synthesis)

3. G2 - (GAP PAHSE 2)

What happens in G1, S and G2?

• G1 - cell grows + increase in volume as new cytoplasm and organelles are made

• S - cell replicates its DNA before

• G2 - cell continues to grow, synthesis of enzymes and structures needed for mitosis

What is the formula to calculate time take for each stage in mitosis?

Cells in that phase / total number of cells undergoing mitosis * total time of 1 cell cycle

There are 100 cells undergoing mitosis. 10 of the cells are in metaphase. The cell cycle for these cells is 15 hours (900 mins)

• how long does a cell spend in metaphase?

10/100×900=90 mins

What does mitotic index show?

Proportion of cells undergoing mitosis in a piece of tissue

How do you calculate mitotic index (MI)

Number of cells underground mitosis / total cell in sample

How can we know number of cells undergoing mitosis from and image?

Number of cells with visible chromosomes

What is MI useful for determining?(2)

• If a tissue is becoming cancerous

• Effectiveness of cancer treatment

How does cancer arise?

• mitosis is usually a controlled process by genes

• Normally when cells have divided enough to make enough new cells they stop

• But when genes that control that division mutate, this can lead to uncontrolled cell division and the formation of tumours and cancers

What is a benign tumour?

A benign tumour does not spread to other parts of the body and grown slow.

What is a malignant tumour?

A malignant tumour are (Cancer) tumours that invade neighbouring tissues and grow quickly

How do cancer treatments work?

work by disrupting the cell cycle, which kill tumour cells

What is a con and pro of cancer treatments?

• Treatments cannot distinguish normal cells from tumour cells = normal cells are affected too

• Tumour cells divide more frequently so treatment is more likely to kill tumour cells

What are three treatments of cancer!

• Surgery

• Radiotherapy

• Chemotherapy

How is surgery used to treat cancer and what is a con?

• in surgery the tumour can be removed

• Can be difficult because of the location eg head

How is radiotherapy used as a treatment for cancer?

• radiation damages DNA at several points in the cell cycle DNA is checked for damage

• If severe damage is detected the cell kills itself preventing further tumour growth

How is chemotherapy used to treat cancer?

This is where drugs are used to kill cancerous cells by preventing them from dividing or damaging them so that they kill themselves

What’s an example of chemotherapy?

Drugs that prevent the synthesis of enzymes required for DNA replication, the cell cannot enter the S phase and kills itself

What is the cell division in prokaryotic cells called?

Binary fission

How fast can binary fission be?

1 division per 20 mins

What happens in binary fission?

• cell replicates genetic material

• then splits into genetically indentical daughter cells

What is the process of binary fission?(3)

1. Replication of DNA and plasmids

2. Circular DNA strands move to opposite poles

3. Cytoplasm divided and new cell wall grow to divide the original cell into two identical daughter cells each with one copy of the circular DNA and a variable number of plasmids