DNA and Chromosomes - MCB L4

Question 1

Give the 4 phases of cell cycle, in order

Answer 1

G1, S, G2, M

Question 2

What happens during the G phases?

Answer 2

The cell grows e.g. ATP accumulation

Question 3

Which phases comprise interphase?

Answer 3

G1, S, G2

Question 4

Centrosomes

Answer 4

Things at each pole of cell

Question 5

Centriole

Answer 5

Organelle inside centrosome that releases spindle

Question 6

Centromere

Answer 6

Between sister chromatids

Question 7

Give the stages of M phase in order

Answer 7

Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis

Question 8

Telomeres

Answer 8

Repeating, non-coding sequences at ends of chromosomes to protect chromosome by protecting coding sequences

Question 9

Kinetochore

Answer 9

Intimately associated with centromere. Spindle fibres join to kinetochore.

Question 10

Prophase

Answer 10

Nucleolus disappears. Chromosomes condense. Mitotic spindles form from centrosomes.

Question 11

Prometaphase

Answer 11

Nuclear membrane disintegrates. Centrosomes move to opposite poles. Kinetochores form and spindle attaches to kinetochores.

Question 12

Metaphase

Answer 12

Chromosomes align at equator

Question 13

Anaphase

Answer 13

Sister chromatids separate, centromeres split in two. Now called chromosomes. Pulled towards opposite poles.

Question 14

Telophase

Answer 14

Chromosomes arrive at poles. Spindle breaks down. Nuclear envelope reforms

Question 15

Cytokinesis

Answer 15

Cytoplasm divides resulting in two genetically near-identical cells. All other components e.g. Golgi are randomly assigned between cells as they can make whatever they lack

Question 16

What molecules regulate cell cycle? How do they regulate it?

Answer 16

Protein kinases and cyclins; they regulate the cell cycle through a series of phosphorylation and dephosphorylation reactions.

Question 17

If something is sensed to be wrong in the cell cycle, what occurs?

Answer 17

Cell cycle stops or cell dies (apoptosis)

Question 18

What may occur if the control mechanisms in cell cycle fail?

Answer 18

Cancer

Question 19

Which phases do chemotherapy drugs target? What side effect does this have?

Answer 19

S and M phases. This means that rapidly replicating cells such as hair cells are killed

Question 20

If not enough ATP in a cell to divide, what happens?

Answer 20

The cell cycle is paused: the control mechanisms signal to ‘wait’

Question 21

What happens in S phase?

Answer 21

DNA replication

Question 22

What happens in M phase?

Answer 22

Nuclear division and cell division

Question 23

The breaking of the triphosphate bond in nucleotides is useful for what reason?

Answer 23

Provides energy for formation of covalent phosphodiester bond between nucleotide and next nucleotide

Question 24

What is the benefit of having multiple replication forks?

Answer 24

Allows for genome to be copied far quicker

Question 25

What are the names of the two parts of the replication fork?

Answer 25

Leading strand, lagging strand

Question 26

Leading strand. What kind of synthesis?

Answer 26

3' end moving towards fork. Continuous synthesis

Question 27

Lagging strand. What kind of synthesis? Why does it have gaps? What are the fragments called?

Answer 27

3' end moving away from fork. Discontinuous synthesis. DNA polymerase works in 5' to 3' direction. So once it has polymerised one part of strand, a new bit has appeared nearer to fork. So polymerase rejoins nearer to fork, leaving gaps and making double stranded Okazaki fragments. Gaps filled by DNA ligase.

Question 28

DNA primase

Answer 28

Adds an RNA primer, a foothold for polymerase to bind to. Primer is on both strands.

Question 29

Nuclease

Answer 29

Removes primer after polymerase has synthesised DNA. Also removes damaged DNA/ wrong nucleotides.

Question 30

DNA ligase

Answer 30

Comes in after nuclease. Tidies up, connects fragments

Question 31

Is DNA primase more active on one strand than the other? Why?

Answer 31

More active on lagging strand as it has to keep adding more primers.

Question 32

Werner Syndrome

Answer 32

Arises from mutation in DNA helicase. Errors in DNA replication and DNA repair. Cells replicate slower so start to show diseases found in elderly.

Question 33

Name two methods of preventing accumulation of mutations

Answer 33

Proof-reading capacity of DNA polymerase. Excision repair systems.

Question 34

Proof reading capacity of DNA polymerase

Answer 34

During DNA replication, DNA polymerase is proof-reading the strands. If wrong nucelotide inserted, the position of the free 3' end of the nucleotide is changed so next nucleotide cannot bind so DNA polymerase stalls, preventing mutation. Wrong nucleotide removed by nuclease.

Question 35

Excision repair systems

Answer 35

Throughout cell life, they repair any damage to DNA

Question 36

What internal sources can damage DNA?

Answer 36

Products of normal cell function. Cell produces oxygen free radicals and hydrogen peroxide

Question 37

What external sources can damage DNA?

Answer 37

Mutagenic chemicals (benzene, cigarette smoke), UV, ionising radiation

Question 38

Synonymous SNP

Answer 38

No change in amino acid sequence due to SNP, so function of protein unchanged so not associated with disease state.

Question 39

Non-synonymous SNP

Answer 39

Change to amino acid sequence due to SNP so function of protein changed so associated with disease state.

Question 40

Somatic mutation

Answer 40

Bad for the individual, affects a particular cell type.

Question 41

Germ line mutation

Answer 41

Affect every cell in offspring

Question 42

What are monogenic genetic diseases?

Answer 42

Diseases arising due to a single gene disorder

Question 43

Name 3 examples of monogenic genetic diseases, stating what type of mutation is responsible for each and whether the disease is associated with loss or gain of function

Answer 43

Substitution: Sickle-cell anaemia. Loss of function. Deletion: Cystic fibrosis. Loss of function. Insertion: Huntington's disease. Gain of function

Question 44

Sickle Cell Disease

Answer 44

Due to single nucleotide substitution in HBB gene (beta-globin chain of haemoglobin). Haemoglobin molecules become sticky, leading to sickle shaped RBCs. Die quickly, so causes anaemia, and clogs up capillaries

Question 45

Cystic Fibrosis

Answer 45

3 base pair deletion in CTFR gene which causes protein to not be transported properly so not expressed on outside of cells. The protein is a transmembrane protein involved in chloride transport. So messes up chloride transport particularly in lungs so abnormal mucus leading to infection. Impaired chloride transport so loss of function

Question 46

Huntington's disease

Answer 46

Insertion. Neurogenerative disease. Due to increase in number of CAG repeats in HTT gene. HTT gene is expressed in nerve cells. CAG encodes glutamine and polyglutamine and polyglutamine is sticky so polyglutamines stick together to make a toxic product which kills nerve cells

Question 47

What determines the severity of Huntington's disease and how early you will get it?

Answer 47

The number of CAG repeats; the more polyglutamine the more toxic the gene.

Question 48

How is Huntington's disease a gain-of-function mutation?

Answer 48

Because of the production of a toxic molecule.