D2.1 - CELL & NUCLEAR DIVISION

Question 1

Describe how new cells are produced

Answer 1

1. All new cells are produced in living organisms by cell division
2. Cell division is when a parent/mother cell divides to produce 2 daughter cells
3. Mitosis: produces 2 identical daughter cells
4. Meiosis: produces 2 genetically unique daughter cells
5. Binary fission: produces identical cells in bacterial reproduction

Question 1

Explain why cells divide/proliferate

Answer 1

1. GROWTH: multicellular organisms consist of trillions of cells
2. CELL REPLACEMENT: tissue repair of skin, or epithelial cell lining of cells are replaced
3. EMBRYONIC DEVELOPMENT: embryo divides to form a morula (ball of cells) and then a blastocyst
4. ASEXUAL REPRODUCTION: bacteria reproduce via binary fission -> 2 identical bacterial cells

Question 2

Impact the impact of cell division on surface area and volume

Answer 2

1. As cell grows larger, SA:Volume ratio DECREASES
2. Cell size is limited by the SA: volume ratio
3. Cells require a large SA: volume ratio to exchange materials by diffusion
4. When a cell becomes too large, the cell divides

Question 3

Explain the phases of the cell cycle

Answer 3

The cell cycle is a time period in which the cell grows and divides: involves interphase, mitosis and cytokinesis

1. INTERPHASE G1 - normal growth of the cell
   - DNA transcription, mRNA production
   - translation/protein synthesis
   - cell respirtaion
   - cell growth
   - increase in cell volume
   - organelle doubling
   - increase in energy stores
2. INTERPHASE S1 - synthesis of genetic material
   - DNA replication
   - duplication of chromosomes into identical sister chromatids
3. INTERPHASE G2 - growth and production of components needed for cell division
   - microtubules produced in preparation of nuclear/cell division
4. MITOSIS: division of the nucleus
   - small part of cell cycle
   - propose, metaphse, anaphase, telophase
   - chromosomes condense, line up and separate
   - produce 2 genetically identical cells
   - occurs in all cells
5. CYTOKINESIS: cytoplasm splits

Question 4

Outline the roles of mitosis and meiosis in eukaryotes

Answer 4

1. BOTH mitosis & meiosis: involve nuclear divison to avoid anucleate cells (no nucleus), produce daughter cells from parent cell after cell divides
2. MITOSIS: daughter cells have the same number of chromosnes and genome as the parent cells, 2n (diploid) and then cell division
   - replaces cells, repairs tissue
   - asexual reproduction
   - growth of multicellular organisms/ increases cell numbers
3. MEIOSIS: genetically unique daughter cells produces from a parent cell
   - generates genetic diversity
   - daughter cells have half the number of choromsones as the parent cell (haploid)
   - 2 divisions -> 4 sperm cells OR one egg (and polar bodies)

Question 5

Explain DNA replication in mitosis and meiosis

Answer 5

1. DNA replication is the prerequisite for both mitosis and meiosis during the S phase of interphase
2. Makes a copy of genetic/hereditary material
3. After DNA replication, each chromosome consists of sister chromatids/duplicated chromosomes

Question 6

Outline the condensation of chromones in mitosis and meiosis

Answer 6

1. DNA is condensed into chromones by supercoiling
2. Becomes nucleosomes (chromatin structural unit of organisation)
3. DNA wrapped around histone proteins twice
4. 8 histone proteins
5. 1 linker histone protein between nucleosomes
6. Electrostatic interaction/acttraction between negatively charged phosphate and positively charged protein

Question 7

Outline the movement of chromosomes of mitosis and meiosis

Answer 7

1. Chromosomes are moved during cell division using microtubules and microtubule motors
   - metaphase (middle)
   - anaphrase (apart, opposite sides of the cell)
2. Microtubules/spindle fibres shorten via polymerisation and depolymerization of tubulin
3. Spindle fibres attach to the centromere/kinetochore and pull the chromosomes apart in anaphase

Question 8

Outline the different phases of mitosis:

Answer 8

4 phases: prophase, metaphase, anaphase, and telophase

1. PROPHASE: DNA supercoils into structures called chromosomes
   - DNA wraps 2x around 8 histone proteins to reduce the size by 10,000 times
   - The nuclear membrane disintegrates
   - Spindle fibres appear (made of microtubules/protein filaments)
   - Centrosomes migrate to opposite poles of the cell
   - Centrioles migrate to opposite ends of the cell
2. METAPHASE: Sister chromatids line up at the metaphase plate
   - Spindle fibres attach to the centromere
   - sister chromatids: replicated/identical chromosomes attached together by the centromere (region where the two chromatids are attached to each other)
3. ANAPHASE: sister chromatids separate and the chromosomes are pulled to opposite sides by the microtubules, centromere splits
4. TELOPHASE: Nuclear membrane reforms
   - spindle fibre apparatus disintegrates
   - Chromosomes unravel into chromatin, a loose form of DNA and protein

Question 9

Outline cytokinesis

Answer 9

1. Cytokinesis: process where the cytoplasm is split into parent cell to separate daughter cells
2. Occurs after mitosis/meisosis and is different between plant and animal cells
3. ANIMAL : contractile proteins (actin and mysosin) form a ring and pinches the cell membrane together, forming a cleavage furrow
4. PLANT: membrane-enclosed vesicles derived from golgi apparatus migrate to the centre of the cell, fusing to form tubular structure so the cell plate/wall can develop

Question 10

Outline the difference between equal and unequal cytokinesis

Answer 10

EQUAL: Mitosis, spermatogenesis
- division of cytoplasm is usually equal
- both daughter cells must receive one mitochondrion and other organelles from a pre-existing structure

UNEQUAL: Oogenesis, budding
- egg and polar body formation in oogenesis
- budding in yeast cell

Question 11

Explain meiosis as a reduction division

Answer 11

1. 2 divisons of meiosis
2. The reduction of the chromosome number occurs in anaphase
3. 2n -> n: Diploing parent cells produce haploid gametes

Question 12

Outline the control of the cell cycle using cyclins

Answer 12

1. Cyclins are a family of 4 proteins (DEAB) that control the cell cycle
2. They bind and activate cyclin-dependent kinase enzymes (CDK’s)
3. CDK’s phosphorylate other proteins -> triggers specific functions in the cell
4. Level of cyclins rise (surge/reach a particular concentration) and fall at different stages: the conditions inside/outside the cell affect regulation
5. Triggers the next stage

Question 13

Explain the consequences of mutations in genes that control the cell cycle. Outline the causes of gene mutation

Answer 13

1. CANCER: abonrmal growth of cells due to a GENE MUTATION (change in DNA) with an oncogene (genes that regulate cell growth/divison)
   - can be malignant (aggressive) tumour
   - benign (does not spread, non cancerous)
2. TUMOURS: abnormal growth of tissue that can develop at any stage of life in any part of the mody

CAUSES OF GENE MUTATION:

1. Mutagens: viral, chemical or UV radiation that can turn oncogenes (genes that regulate cell growht/cell division) to be cancerous (divides uncontrollably)
2. Errors in DNA replication or repair

Question 14

Describe the differences between tumours in rates of cell division/growth and the capacity for metastasis and invasion of neighbouring tissue

Answer 14

Tumours can be cancerous or b ening, and are a collection of cells

1. Primary tumour: mass of cells formed at the origin
2. Cancerous tumours: higher rate of cell division/growth, can metastasise/spread/invade other issue
3. Secondary tumours: originated form cancerous primary tutor that has been spread by metastasis, are malignant
4. Benging tumours; collection of cells that have divided but are not cancerous