C19 - Genetics

Question 1

What is a mutation?

Answer 1

Change in the sequence of bases in DNA which may affect the phenotype of the organisms

Question 2

What is a mutagen?

Answer 2

Chemical or physical agents which cause a mutation

Question 3

Examples of mutagens

Answer 3

Ionisation radiation (X-Rays)
Deaminating agents
Alkylating agents
Base analogs
Viruses

Question 4

What are the types of mutations?

Answer 4

Substitution / deletion / insertion of one or more nucleotides within a gene

Question 5

What are point mutations?

Answer 5

When only one nucleotide is affected by mutation

Question 6

What is substitution?

Answer 6

Mutation where one or more nucleotides are substituted for another in a DNA strand

Question 7

What is insertion?

Answer 7

Mutation where one or more extra nucleotides are inserted into a DNA strand

Question 8

What is deletion?

Answer 8

Mutation where one or more nucleotides are deleted and lost from the DNA strand

Question 9

What is a frameshift mutation?

Answer 9

Caused by insertion or deletion of a nucleotide
It causes the reading frame to move (read in triplets)
If a multiple of 3 added or deleted

Question 10

What effects can mutations have?

Answer 10

No effect - doesn’t change phenotype BC normally function proteins still synthesised
Damaging - changes phenotype negatively BC proteins no longer synthesised or are non-functional
Beneficial - rare

Question 11

What is a chromosome mutation?

Answer 11

Affects whole chromosomes / a number of chromosomes in a cell

Question 12

Types of chromosome mutations?

Answer 12

Deletion - section of chromosome breaks off and is lost within cell
Duplication - sections are duplicated on a chromosome
Translocation - section of a chromosome breaks off and joins another non-homologous chromosome
Inversion - section of chromosome breaks off, is reversed, joins back onto chromosome

Question 13

What is a silent mutation?

Answer 13

Does not change any proteins or the structure of proteins synthesised
Could change primary structure, not overall
Have no effect on the phenotype
Occur in non-coding regions of DNA / code for same amino acid (degenerate code)

Question 14

What are non-sense mutations?

Answer 14

Cause codon to become stop codon rather than amino acid
Shortens protein
Usually make it non-functional
Usually have negative/harmful phenotypes

Question 15

What are missense mutations?

Answer 15

Cause incorporation of incorrect amino acid into primary structure when protein is synthesised
Mutation could be silent, beneficial or harmful

Question 16

What is a conservative mutation?

Answer 16

Occurs when new amino acid has similar properties to original

Question 17

What is a non-conservative mutation?

Answer 17

Occur when new amino acid has different properties to original so more likely to have effect on protein structure

Question 18

How are genes regulated?

Answer 18

Transcriptional - genes turned on or off
Post-transcriptional - mRNA modified regulating translation + types of proteins produced
Translational - translation stopped or started
Post-translational - proteins modified after synthesis changing their functions

Question 19

What factors affect the transcription of genes?

Answer 19

Chromatin remodelling
Histone modification
Lac operon
Cyclic AMP

Question 20

How does chromatin remodelling affect the transcription of genes?

Answer 20

Heterochromatin is tightly wound DNA causing chromosomes to be visible during cell division
Euchromatin is loosely wound DNA present during interphase

Transcription not possible when when DNA tightly wound
BC RNA polymerase cannot access genes in heterochromatin
SO protein synthesis cannot occur during cell division but occurs in interphase
ENSURES proteins necessary for cell division are synthesised in time AND prevents energy consuming process of protein synthesis occurring during cell division

Question 21

How does histone modification affect the transcription of genes?

Answer 21

DNA coils around histones as they are +vely charged and DNA is -ve

Histone scan be modifies to inc/dec packing

Addition of acetyl groups/phosphate groups reduces +ve charge on histones causing DNA to coil less tightly, allowing certain genes to be transcribed

Addition of methyl groups makes histones more hydrophobic, bind tightly to each other, DNA coils more tightly, prevents transcription of genes

Epigenetics describes this control of gene expression by modification of DNA

Question 22

How does lac operon affect the transcription of genes?

Answer 22

Operon - group of genes that are under control of same regulatory mechanism and are expressed at the same time

Glucose easier to metabolise + preferred respiratory substrate of many bacteria
If glucose in short supply, lactose used as respiratory substrate which need dif enzymes to metabolise it

Lac operon is group of 3 genes (lacZ,lacY,lacA) involved in metabolism of lactose
Is a structural protein coding for 3 enzymes which are transcribed onto a single long molecule of mRNA

Regulatory gene (lac I) prevents transcription of structural gene in absence of lactose
Repressor protein constantly produced and binds to operator area, close to structural genes
Binding prevents RNA polymerase binding to DNA at the promoter, preventing transcription
Down regulation

When lactose is present it binds to repressor protein changing its shape so it can no long bind to operator
RNA polymerase can bind to promoter, 3 structural genes transcribed, enzymes synthesised

Efficient way of saving resources as if certain gene products not needed, all genes involved in production switched off
(more common in prokaryotes than eukaryotes - simpler, smaller structure of genomes)

Question 23

How does cyclic AMP affect the transcription of genes?

Answer 23

Binding of RNA polymerase results in relatively slow rate of transcription
Needs to be up-regulated to produce required quantity of enzymes to metabolise lactose
cAMP receptor protein (CRP) binds, CRP bound to cAMP
Transport of glucose into bacteria decreases levels of cAMP, reducing transcription of genes responsible for metabolism of glucose

Question 24

What is epigenetics

Answer 24

External control of genetic regulation

Question 25

What is a regulatory and a structural gene

Answer 25

Gene that codes for protein involved in DNA regulation Genes that code for structural proteins/enzymes not involved in DNA regulation

Question 26

Examples of post-transcriptional/pre-translational control

Answer 26

RNA processing -Product of transcription is precursor molecule (pre-mRNA) Modified forming mature mRNA before it binds to ribosome and code for synthesis of protein -Cap (modified nucleotide) added to 5' end and tail (long chain of adenine nucleotides) added to 3' end Stabilise mRNA and delay degradation in cytoplasm Aids binding of mRNA to ribosomes -Splicing occurs where RNA cut at specific points, introns removed and exons joined (within nucleus) RNA editing -Nucleotide sequence of mRNA molecules can be changed thru base addition, deletion, substitution Same effect as point mutations Result in synthesis of proteins which may have different functions Inc range of proteins that can be produced by single mRNA molecule or gene

Question 27

What are examples of translational control?

Answer 27

Regulate protein synthesis -Degradation of mRNA: more resistant molecule, longer it will last in cytoplasm, greater quantity of protein synthesised -Binding of inhibitory proteins to mRNA prevents it binding to ribosomes, preventing protein synth -Activation of initiation factors aid binding of mRNA to ribosomes Protein kinases -Enzymes that catalyse the addition of phosphate groups to proteins changing its tertiary structure and function -Many enzymes activated by phosphorylation -Activated themselves by cAMP

Question 28

What are examples of post translational control

Answer 28

Modifications to proteins that have been synthesised -Addition of non protein groups -modifying amino acids and formations of bonds eg disulfide bridges -folding/shortening of proteins -modification by cAMP

Question 29

What is a homeobox gene?

Answer 29

/Hox genes Genes responsible for development of body plan Control mitosis and apoptosis

Question 30

What is a homeobox

Answer 30

Section of DNA 180 base pairs long coding for a part of the protein 60 amino acids long that is highly conserved in plants, animals and fungi

Question 31

What is a homeodomain

Answer 31

Part of the protein coded for by the homeobox genes, binds to DNA and switches other genes on/off

Question 32

What type of genes are homeobox genes?

Answer 32

Regulatory genes

Question 33

What are hox genes

Answer 33

One group of homeobox genes that are only present in animals Responsible for correct positioning of body parts

Question 34

How are Hox genes found in mammals

Answer 34

Gene clusters Mammals have 4 clusters on each chromosome Order in which genes appear along chromosome is order in which effects are expressed

Question 35

How many Hox genes do humans have

Answer 35

39

Question 36

How are body plans usually represented?

Answer 36

Cross section showing fundamental arrangement of tissue layers

Question 37

What is a diploblastic and triblastic animal

Answer 37

2 and 3 primary tissue layers

Question 38

How do Hox genes and segmentation work together in animal development?

Answer 38

Many animals have segmented bodies In embryos segments are called somites, become specialised body parts (eg ribs, limbs, mouthparts) Hox genes control what each segment turns into based on its position

Question 39

How is symmetry shown in animals

Answer 39

Radial symmetry seen in diploblastic animals - no left/right just top + bottom Bilateral symmetry seen in most animals - left + right, head + tail Asymmetry seen in sponges - no line of symmetry

Question 40

What is the role of mitosis and apoptosis in shaping organisms

Answer 40

Mitosis inc number of cells leading to growth Apoptosis shapes different body parts by removing unwanted cells and tissues -cells undergoing apoptosis can release chemical signals stimulating mitosis and cell proliferation, remodelling tissues

Question 41

What factors affect the expression of regulatory genes?

Answer 41

Internal + external factors Stress - condition produced when homeostatic balance in organism is disrupted External -temp -light intensity Internal -hormones -psychological stress -drugs