Chapter 19- Genetics of living systems

Question 1

What are the three types of mutation in genetic material

Answer 1

Substitution, deletion or insertion

Question 2

What is a point mutation?

Answer 2

If only one nucleotide is affected by a mutation

Question 3

What nature of genetic code allows the codon to code for the same amino acid after a point mutation?

Answer 3

Degenerate nature

Question 4

Which types of mutation cause frame shift mutation?

Answer 4

Insertion or deletion

Question 5

What are the three types of consequences of a mutation?

Answer 5

No effect
Damaging
Beneficial

Question 6

What is a mutagen?

Answer 6

A chemical, physical or biological agent that causes mutations

Question 7

Name some alternative causes to mutation

Answer 7

Depurination, depyrimidination

Question 8

Give an example of a physical, biological and chemical mutagen and explain each one

Answer 8

Physical- Ionising radiation (eg X-rays) breaks one or both DNA strands
Chemical- deaminating agents- chemically alter bases in DNA, changing the base sequence
Biological- Viruses, viral DNA inserts itself, changing the base sequence

Question 9

What is a silent mutation?

Answer 9

A mutation that does not change any proteins or their activity

Question 10

What is a nonsense mutation?

Answer 10

Nonsense mutations result in a codon becoming a stop codon, instead of coding for an amino acid, resulting in a shortened protein

Question 11

What is a missense mutation?

Answer 11

Results in the incorporation of an incorrect amino acid into the primary structure when a protein is synthesised.

Question 12

What is the difference between conservative and non-conservative mutations?

Answer 12

Conservative- mutated codons have a similar effect to the original codons, meaning there is not a large overall effect
Non-conservative- amino acid has completely different properties, more likely to have an effect on protein structure

Question 13

Give an example of a beneficial mutation

Answer 13

The ability to digest lactose

Question 14

How could having sickle cell anaemia be beneficial?

Answer 14

Develop resistance to malaria

Question 15

How can changes in chromosome structure cause mutation?

Answer 15

Deletion- section of chromosome breaks off and is lost
Duplication- section of the chromosomes are copied
Translocation- a section of one chromosome breaks off and rejoins another
Inversion- a section breaks off, spins around and rejoins another

Question 16

What is a housekeeping gene?

Answer 16

A gene that codes for proteins necessary for constant reactions like respiration

Question 17

Why do genes have to be regulated?

Answer 17

Because every cell contains the entire genome, but not all the genes are required by all the cells, and so by regulating genes material is not wasted

Question 18

What are the four ways that genes are regulated?

Answer 18

Transcriptional- genes can be turned on and off
Post transcriptional- mRNA is modified to regulate translation
Translational- translation is stopped or started
Post translational- proteins are modified after synthesis

Question 19

What is the difference between heterochromatin and euchromatin?

Answer 19

Heterochromatin is tightly wound around histones, but euchromatin is loosely wound and only present during interphase

Question 20

Why does DNA coil around histones?

Answer 20

Histones are positively charged and DNA is negatively charged, so the DNA is attracted to histones

Question 21

What impact does the addition of acetyl or phosphate groups have on chromatin?

Answer 21

Reduces the positive charge on histones and causes DNA to coil less tightly

Question 22

Which group causes DNA to bind more tightly to histones?

Answer 22

Methyl groups in methylation make histones more hydrophobic

Question 23

What is the term used to describe histone modification?

Answer 23

Epigenetics

Question 24

Define an operon

Answer 24

A group of genes under the same regulatory expression - much more common in prokaryotic organisms

Question 25

What is the preferred respiratory substrate of E. Coli?

Answer 25

Glucose- easy to metabolise, but lactose can be used as a substrate

Question 26

What has to occur for E. Coli to metabolise lactose?

Answer 26

Involving the lac operon (lacZ, lacY, lacA) In the absence of lactose, the regulatory gene, lacI codes for a repressor protein that binds to operator and prevents the transcription of the digestive enzymes by blocking its path

Question 27

How does lactose being present in a prokaryote stimulate the production of digestive enzymes?

Answer 27

Binds to the repressor protein and changes its structure so it can no longer bind to RNA polymerase, allowing it to transcribe the digestive enzymes

Question 28

What is the role of cyclic AMP in producing lactose digesting enzymes?

Answer 28

binds to cAMP receptor protein (CRP) which triggers the increase in the rate of transcription to efficiently digest lactose Transport of glucose reduces cAMP levels, as it is the preferred respiratory substrate

Question 29

What is produced directly after transcription?

Answer 29

pre-mRNA which has to be modified

Question 30

Which end of the nucleotide is the cap added to?

Answer 30

5’ end

Question 31

What is the purpose of the cap and tail in translation?

Answer 31

Helps to prevent degradation of mRNA in the cytoplasm and aids in the binding of mRNA to ribosomes

Question 32

What are the three mechanisms that regulate protein synthesis?

Answer 32

degradation of mRNA- the more resistant a molecule the longer it will last in the cytoplasm binding inhibitory proteins to mRNA activation of initiation factors

Question 33

Define morphogenesis

Answer 33

The regulation of the pattern of anatomical development

Question 34

What is a homeobox gene?

Answer 34

A group of genes that contain a homeobox- a section of DNA coding for a part of a protein called the homeodain

Question 35

How long is the homeobox?

Answer 35

180 base pairs, coding for 60 highly conserved amino acids

Question 36

What is the homeodain?

Answer 36

The part of the protein coded for by the homeobox that binds to DNA and switches other genes on or off

Question 37

What does Pax6 cause when it mutates? Why is this an important discovery?

Answer 37

Blindness- it does this across many species, indicating that this homeobox gene regulates eye development

Question 38

What is a hox gene and how is it different to a homeobox gene?

Answer 38

A group of homeobox genes found in gene clusters, only present in animals and responsible for the positioning of different body parts

Question 39

How many hox clusters do mammals have?

Answer 39

4

Question 40

What is a diploblastic and tripoblastic animal?

Answer 40

Diploblastic- an animal with two primary tissue layers Tripoblastic- an animal with three primary tissue layers

Question 41

How many Hox genes do humans have in total?

Answer 41

39

Question 42

What is a somite?

Answer 42

the segments in the embryo that individual vertebrate and associated structures develop from

Question 43

Name the three types of symmetry exhibited in different animals

Answer 43

Radial (eg jellyfish) Bilateral (mammals like humans) Asymmetry (sponges, coral)

Question 44

How does apoptosis play a role in body plans?

Answer 44

By cutting back at the mass of cells produced by mitosis to reveal the shape of a structure, regulated by Hox genes

Question 45

What is the drug commonly used that has an effect on Hox genes?

Answer 45

Thalidomide- prevents the normal expression of Hox genes, is being experimented with for cancer treatment