genetics of living systems

Question 1

what are gene mutations

Answer 1

they are a change in the DNA base sequence

Question 2

what is substitution mutation

Answer 2

when one base is replaced by another

Question 3

what is deletion mutation

Answer 3

when one base is removed from the sequence

Question 4

what is insertion mutation

Answer 4

when one base is added to the sequence

Question 5

does substitutions always lead to a change in the amino acid sequence

Answer 5

.no as they substituted base may code for the same amino acid
.this is as genetic code is degenerate

Question 6

how do deletions change the amino acid sequence

Answer 6

.a base is removed from the base sequence which causes a frameshift where the whole sequence after the deletion shifts to the left
.this changes all the triplets leading to a different amino acid sequence

Question 7

how do insertion change the amino acid sequence

Answer 7

.a base is inserted which causes a frameshift of the whole sequence to the right
.this changes all the triplets after the insertion so changing the amino acid sequence

Question 8

what are transcription factors

Answer 8

proteins that bind to specific DNA sequences to initiate the transcription of genes into mRNA

Question 9

what happens when a gene is switched off

Answer 9

transcription factors cannot bind to the DNA and so prevents the transcription process and so the synthesis of polypeptides

Question 10

what is epigenetic regulation

Answer 10

.changing the gene expression without changing the DNA sequence
e.g. by histone modifications

Question 11

what is acetylation

Answer 11

.process where acetyl groups are added to histones
.this decreases their positive charge and so results in a looser DNA coil and increased transcription

Question 12

what is phosphorylation

Answer 12

.adding phosphate groups to histones which reduces their positive charge resulting in a looser DNA coil and increased transcription

Question 13

what is methylation

Answer 13

.adding methyl groups to histones, increasing the hydrophobic interactions and so tightening the coil and decreasing transcription

Question 14

what is chromatin remodelling

Answer 14

changing the structure of chromatin(DNA wrapped around histone protein)

Question 15

what is euchromatin

Answer 15

.loosely packed chromatin making it easier for RNA polymerase to access gene and so enabling transcription

Question 16

what is heterochromatin

Answer 16

.densely packed chromatin making it difficult for RNA polymerase to access genes and so preventing transcription

Question 17

what is a operon

Answer 17

.cluster of genes controlled by a promoter which allows for coordinated expression in prokaryotes

Question 18

key components of operons

Answer 18

regulatory genes- encode protein that regulate the expression of structural genes

.promoter region- this is the site where RNA polymerase binds to initiate transcription

.operator region- sequence where regulatory proteins bind to

.structural gene- genes that code for proteins

Question 19

what is the lac operon

Answer 19

.a operon in the bacterium Escherichia coli that control the metabolism of lactose

.this is so that they can use lactose when there is lack of glucose

Question 20

what does the lacI regulatory gene do

Answer 20

codes for the repressor protein that inhibits the lac operon activity

Question 21

lacZ

Answer 21

.enzyme- beta-galactosidase
.breaks down lactose into glucose and galactose

Question 22

lacY

Answer 22

enzyme- lactose permease
.transports lactose into the cell

Question 23

lacA

Answer 23

enzyme- transacetylase
.modifies lactose or its by products

Question 24

how does the lac operon function when lactose is absent

Answer 24

.repressor protein binds to the operator region
.RNA polymerase is blocked from the promoter region
.RNA polymerase cant transcribe the structural gene
.enzymes for lactose metabolism isn’t produced

Question 25

how does the lac operon function when lactose is present

Answer 25

.lactose bind to repressor protein .repressor protein changes shape and is released from the operator region .RNA polymerase binds to promoter region and initiates transcription .RNA polymerase transcribes the structural genes leading to the production of enzymes used for lactose metabolism

Question 26

how is the lac operon regulated by glucose

Answer 26

.when glucose is present it reduces the cAMP levels = CRP-cAMP complex cannot form = lac operon transcription is downregulated = lactose metabolism enzymes are not produced .when glucose isn't present, cAMP levels increase = CRP-cAMP complex forms and upregulates the transcription of lac operon = lactose metabolism is optimised

Question 27

how is pre-mRNA processed

Answer 27

.5'cap is added which stabilises the mRNA, delays its degradation and assists in ribosome binding .3' poly-A tail is added which stabilises mRNA and delays degradation .splicing introns and joining exons together providing instructions for the protein sequenece

Question 28

how does mRNA degradation rate effect the rate of translation

Answer 28

.mRNA degrades slowly is more stable and lasts longer .this increases translation and protein synthesis

Question 29

how do inhibitory proteins affect the rate of translation

Answer 29

.they bind to mRNA preventing it from attaching to ribosomes .this decreases the translation and protein synthesis

Question 30

how do initiation factors affect the rate of translation

Answer 30

they help mRNA bind to ribosomes initiating translation and so increasing protein synthesis

Question 31

how do protein kinases modify proteins

Answer 31

.they add phosphate groups to proteins via phosphorylation .this changes the proteins tertiary structure .this often activates enzymes (regulated via cAMP)

Question 32

what are some examples of post-translational modification

Answer 32

.addition of carbs, lipids or phosphates .formation of disulfide bridges between amino acids .shortening peptide bonds .folding into 3D shapes .modification via cAMP(in lac operon)

Question 33

what is a body plan

Answer 33

.structured arrangement of an organism's parts .determined by genetics and developmental factors

Question 34

what are homeobox genes

Answer 34

group of regulatory genes with a conserved DNA sequence that guides the development of body plans

Question 35

what is a homeobox sequence

Answer 35

.highly conserved DNA sequence found in homeobox genes that is used for the development of an organism's body plan

Question 36

what is a hox gene

Answer 36

.set of homeobox gene in animals .contains homeobox sequences for correcting positioning of body parts

Question 37

process if how hox genes control development

Answer 37

homeobox sequence encode the homeodomain .homeodomain operates as a transcription factor and binds to DNA switching developmental genes on or off

Question 38

what things can hox genes control

Answer 38

.num of body layers .symmetry of body .anterior-posterior axis (making sure that the head and tail are at opposite ends of the body) segmentation of the body into head, thorax, abdomen .position and development of limbs

Question 39

why are homeobox genes so conserved

Answer 39

.mutations can alter the body plan .genes would be affected within the homeobox gene .this makes mutations lethal and selected against

Question 40

how apoptosis and mitosis shape the body plan

Answer 40

they are used to refine the body morphology e.g. mitosis is used to grow embryonic fingers and apoptosis is used to removed the webbing between fingers

Question 41

how do developmental genes respond to internal stimuli

Answer 41

.regulatory genes respond to stress, drugs and hormones that can cause DNA damage .if DNA is damaged then regulatory genes trigger the cell cycle to stop and initiate apoptosis

Question 42

how do developmental genes respond to external stimuli

Answer 42

.regulatory genes respond to changes like temp or light intensity e.g. lack of nutrients = trigger cell division