1
Q
what’s a mutation
A
a random change to the genetic material
2
Q
define mutagenic
A
factor that increases chance of mutation
3
Q
what’s a gene mutation
A
change to DNA
4
Q
are somatic mutations passed on to offspring
A
no, but those in meiosis are
5
Q
what are the 2 ,main classes of DNA mutation
A
- point mutation: one base is substituted for another
- indel mutation: one or more nucleotides are inserted or deleted from a length of DNA, may cause a frameshift
6
Q
what are the three types of point mutations
A
- silent
- missense
- nonsense
7
Q
what are silent mutations
A
- change in triplet base, where that triplet still codes for the same aa so protein structure isn’t altered
- due to degeneracy of the genetic code
8
Q
what are missense mutations
A
- change to the base triplet sequence that leads to a change in aa sequence in protein
- alteration to 1* structure leads to change 3*, altering shape + preventing usual function
9
Q
what are nonsense mutations
A
- point mutations may alter a base triplet so that it becomes a termination triplet
- results in truncated protein that won’t function
- protein degraded in cell
10
Q
what are indel (insertions and deletions) mutations
A
- if nucleotide base pairs ( not in multiples of 3) are inserted in or deleted from a gene, because the code is non-overlapping and read in triplets, all subsequent triplets are altered (frameshift)
- protein made can’t carry out function
- insertion or deletion of a triplet of base pairs result in loss or addition of an aa
11
Q
what are expanding triplet nucleotide repeats
A
- some genes contain repeating triplets such as -CAG CAG CAG-
- no. of CAG triplets increases at meiosis and again from generation to generation
12
Q
what are some benefits of mutations
A
- helped drive evolution through natural selection
- blue eyes useful for seeing in less bright light
- black skin has high conc of melanin protecting from sunburn + skin cancer
13
Q
what are some neutral mutations
A
- inability to smell certain flowers
- differently shaped earlobes
14
Q
define exon
A
the coding, or expressed, region of DNA
15
Q
define intron
A
non-coding part of DNA
16
Q
define operon
A
a group of genes that function as a single transcription unit
17
Q
what’s a transcription factor
A
protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of a gene
18
Q
give an example of an operon in prokaryotic cells involved in the regulation of gene expression
A
lac operon
19
Q
what can the bac E.coli metabolise instead when glucose isn’t present
A
lactose
20
Q
what 2 enzymes does lactose induce the production of in E.coli
A
- lactose permease
- B galactosidase
21
Q
what’s the lac operon
A
a length of DNA with an operator region next to the structural genes lac Z and lac Y that code for the 2 enzymes
22
Q
relative positioning of structures in lac operon and what they are
A
I | |P|lac O |lac Z|lac Y
I = regulatory gene
P + lacO = control sites
P = promoter region
lacO = operator region
lac Y + lac Z = structural genes
23
Q
what’s the role of lactose permease
A
allows lactose to enter the bacterial cell
24
Q
what’s the role of B galactosidase
A
hydrolyses lactose to a glucose and B galactose
25
what's the role of I (regulatory gene)
- codes for repressor protein (lacI) by producing mRNA which is translated into a protein by ribosome
26
role of repressor protein (lac I )
- when the gene is expressed, protein produced binds to **operator region** preventing RNA polymerase from binding to promoter region so **lac Y and lac Z not transcribed**
- enzymes not made, genes are "off"
27
how does the presence of lactose affect the repressor protein
- lactose bonds to lac I, altering its shape, preventing it from binding to operator
- RNA polymerase can bind to promoter region + transcribe structural gene into mRNA which is translated into the 2 enzymes
28
do all eukaryotic cells have the same genome
- yes, but different genes are expressed in diff cells for differentiation
- all the basic '**housekeeping' genes** are expressed
- transcription factors slide along DNA molecule, binding to their promoter regions and either aid or inhibit the attachment of RNA polymerase to the DNA so activates or suppresses transcription of diff genes in diff cells
- involved in cell cycle, **tumour suppressor genes** regulate cell division, if it mutates it can lead to **cancer**
29
what's involved in **post-transcriptional** gene regulation in eukaryotic cells
introns and exons
30
describe **post-transcriptional** gene regulation in eukaryotic cells
- all DNA of a gene including introns and exons is transcribed producing primary mRNA
- **1* mRNA** is edited by removing RNA introns
- remaining mRNA exons are joined together
- **endonuclease** involved in editing + splicing
31
some introns may encode proteins and some may become...
short non-coding lengths of RNA involved in gene regulation
32
how can a length of a DNA encode more than one protein
depending on how its spliced
33
what's involved in **post-translational** gene regulation in eukaryotes
- activation of proteins
- many enzymes are activated by being phosphorylated
34
outline the process of **post-translational gene regulation** in eukaryotes
1. signalling molecule binds to a receptor on plasma membrane of target cell
2. transmembrane protein activated which then activates a G protein
3. activated G protein activates adenyl cyclase enzymes
4. activated adenyl cyclase enzymes catalyse formation of many cAMP from ATP
5. cAMP activates **PKA**
6. activated PKA **catalyses phosphorylation of proteins, hydrolysing ATP in the process**
7. PKA may phosphorylate another protein (CREB)
8. this then enters the nucleus and acts as a **transcription factor**, regulating transcription
35
define apoptosis
programmed cell death
36
define conserved
has remained in all descendent species throughout evolutionary history
37
what's the homeobox sequence
sequence of 180 base pairs ( excluding introns) involved in **regulating patterns of anatomical development in animals, plants and fungi**
38
what are hox genes
subset of homeobox genes, found only in animals, involved in formation of anatomical features in correct locations of body plan
39
what's the homeodomain sequence
- **60 aa sequence** encoded by 180 DNA base pairs
- can fold into a particular shape and bind to DNA, **regulating transcription** of adjacent genes
- contains 2 alpha helices connected by one turn (H-T-H)
40
how do hox genes control the body plan development in animals
- regulate the development of embryos along the **head-tail axis**
- control the position of body parts, helps form basic body pattern
- if these genes mutate, abnormalities occur
- controls **polarity** of organisms ( which end will develop into the head/tail)
41
what do hox genes encode
homeodomain proteins
42
how do homeodomain proteins act as transcription factors
- act on the nucleus and activate other genes that promote **cell division, apoptosis and helps regulate cell cycle**
43
are hox genes similar across different classes of animals
yes
44
what genes are hox genes regulated by
gap genes and pair-rule genes
45
which genes regulate mitosis
- **homeobox and hox genes**
- ensure that each daughter cell contains the full genome + is a clone of parent cell
- some genes are "switched off" so not expressed during differentiation
46
outline the process of apoptosis
1. enzymes break down **cytoskeleton**
2. cytoplasm becomes dense
3. protrusions (plebs) form in the plasma membrane
4. chromatin condenses, nuclear envelope breaks down and DNA breaks into fragments
5. cell breaks into **vesicles** that are ingested by phagocytic cells, so debris don't damage other cells or tissues
47
how is apoptosis controlled
- **signalling molecules** released when genes involved in **regulating cell cycle** and apoptosis respond to external or internal stimuli ( **stress**)
48
examples of signalling molecules involved in apoptosis
cytokines, hormones, growth factor, nitric oxide
49
why is apoptosis important
- causes **digits to separate**
- removes **ineffective or harmful T-lymphocytes** during development of immune system
50
why should rate of cells dying be equal to rate of cells produced by mitosis
- not enough apoptosis leads to tumours
- too much leads to cell loss + degradation
51
how is the right balance of rate of cells dying and rate of cells produced by mitosis achieved
through cell signalling
