5.1 The Mitotic Cell Cycle

Question 1

Genome

Answer 1

the complete set of genes or genetic material (haploid set) present in a cell or organism.

Question 2

Chromatin

Answer 2

Combination of DNA and histone proteins that makes up eukaryotic chromosomes (loosely coiled form of chromosomes)

Question 3

Chromatid

Answer 3

Two threadlike strands into which a chromosome divides longitudinally during cell division - each contains one molecule double helix of DNA

Question 4

Centromere

Answer 4

Narrow region where two chromatids are joined together

Question 5

Heterochromatin

Answer 5

Eukaryotic chromatin remains highly compacted (easier to separate) & generally not transcribed - genes mostly inactive

Question 6

Euchromatin

Answer 6

Less condensed form of eukaryotic chromatin available for transcription

Question 7

Chromosome

Answer 7

A molecule of DNA, associated with histones (protein) carrying genetic information in the form of genes. The DNA is tightly coiled around the histones, so that the long DNA molecule packs into a very small space

Question 8

Telomere

Answer 8

Regions of non-coding DNA at end of chromosomes which prevents loss of DNA

Question 9

Diploid nucleus

Answer 9

Contains 2 sets of chromosomes; 1 set = 23 chromosomes (2n = 46)

Question 10

Autosomes

Answer 10

All chromosomes except sex chromosomes

Question 11

Haploid nucleus

Answer 11

Contains 1 set of chromosomes (n = 23)

Question 12

Interphase

Answer 12

Phase of the cell cycle in which a typical cell spends most of its life in this phase - cell copies its DNA in preparation for mitosis

Question 13

Interphase stages

Answer 13

• G1: cell makes RNA, enzymes, proteins for growth and at end of G1 the cell becomes committed to dividing or not dividing
• S: DNA replication - each chromosome replicates to have two identical chromatids
• G2: cell continues to grow and new DNA checked for any errors repaired before proceeding to mitosis

Question 14

Mitosis (M Phase)

Answer 14

Nuclear division in which two cells are genetically identical with diploid nucleus

Question 15

Importance of mitosis

Answer 15

• Asexual reproduction
• Cell replacement
• Repairment of damaged tissues
• Cell growth

Question 16

Early prophase

Answer 16

1) Centrioles replicate just before prophase
2) Chromosomes start to appear as the chromatin condenses and coils up, becoming shorter
3) Intact nuclear envelope

Question 17

Late prophase

Answer 17

1) Chromosomes are seen to consist of two identical chromatids; each chromatid contains one DNA molecule
2) Centrioles move to opposite ends of nucleus where they form poles of the spindle
3) Nuclear envelope disappears (it breaks up into small vesicles which are not visible with light microscope)
4) Nucleolus disappears (forms part of several chromosomes)

Question 18

Metaphase

Answer 18

1) Nuclear envelope disappears
2) Each centriole reaches a pole
3) Spindle (microtubules) is completely formed by centrioles
4) Chromosomes continue to condense
5) Spindle fibres attach to the cetromeres of the chromosomes
6) Spindle fibres pull on the centromeres, arranging them at the equator

Question 19

Anaphase

Answer 19

1) Links between sister chromatids break

2) The centromeres of sister chromatids move apart, pulled by the spindle fibres to the poles of the cell

Question 20

Telophase

Answer 20

1) Sister chromatids (now separate chromosomes) reach opposite poles
2) The chromosomes decondense
3) Nuclear envelope begin to form around the chromosomes at each pole
4) The spindle disappears

Question 21

Cytokenesis

Answer 21

The cell divides into 2 cells, either by the infolding of the cell surface membrane in animal cells, or by the formation of a new cell wall and cell surface membrane in plants

Question 22

Mitosis Stages

Answer 22

1) Interphase
2) Early Prophase
3) Late Prophase
4) Metaphase
5) Anaphase
6) Telophase
7) Cytokenesis

Question 23

Significance of Telomeres

Answer 23

1) Rich in base guanine G
2) Proposed that shortening of telomere is somehow connected to ageing process
3) Prevents loss of genes
4) Allows continual cell replication

Question 24

Stem Cells

Answer 24

cells can divide an unlimited number of times - each new cell has a potential to remain a stem cell or to differentiate into a specialised cell

Question 25

Totipotent

Answer 25

a cell that can give rise to all parts of embryo and adult eg. zygote formed by fertilisation - can develop into embryo & placenta

Question 26

Pluripotent

Answer 26

a cell that can give rise to many but not all parts of an organism eg. embryonic stem cells

Question 27

Multipotent

Answer 27

a cell that can give rise to few cell types eg. adult stem cells
- Undifferentiated cells can differentiate into number of different cell types eg. stem cells in bone marrow differentiate into blood cells - WBC, RBC, platelets

Question 28

Tumour

Answer 28

consists of a clone of cells identical to original mutated cell

Question 29

Carcinogen

Answer 29

Any agent that causes cancer and is described as carcinogenic

Question 30

Mutatic Agents

Answer 30

• High fat diet
• X-rays
• Ionising radiation
• Poor checking of chromatids (during interphase)
• Carcinogen / smoking
• Alcohol / drugs
• Pollution

Question 31

Oncogene

Answer 31

cancer-causing genes

Question 32

Pro-oncogene

Answer 32

normal gene coding for protein that stimulates normal cell growth & division

Question 33

Tumor suppressor genes

Answer 33

Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, or tell cells when to die (a process known as apoptosis or programmed cell death). When tumor suppressor genes don’t work properly, cells can grow out of control, which can lead to cancer.