genetics of living systems Flashcards
what are gene mutations
they are a change in the DNA base sequence
what is substitution mutation
when one base is replaced by another
what is deletion mutation
when one base is removed from the sequence
what is insertion mutation
when one base is added to the sequence
does substitutions always lead to a change in the amino acid sequence
.no as they substituted base may code for the same amino acid
.this is as genetic code is degenerate
how do deletions change the amino acid sequence
.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
how do insertion change the amino acid sequence
.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
what are transcription factors
proteins that bind to specific DNA sequences to initiate the transcription of genes into mRNA
what happens when a gene is switched off
transcription factors cannot bind to the DNA and so prevents the transcription process and so the synthesis of polypeptides
what is epigenetic regulation
.changing the gene expression without changing the DNA sequence
e.g. by histone modifications
what is acetylation
.process where acetyl groups are added to histones
.this decreases their positive charge and so results in a looser DNA coil and increased transcription
what is phosphorylation
.adding phosphate groups to histones which reduces their positive charge resulting in a looser DNA coil and increased transcription
what is methylation
.adding methyl groups to histones, increasing the hydrophobic interactions and so tightening the coil and decreasing transcription
what is chromatin remodelling
changing the structure of chromatin(DNA wrapped around histone protein)
what is euchromatin
.loosely packed chromatin making it easier for RNA polymerase to access gene and so enabling transcription
what is heterochromatin
.densely packed chromatin making it difficult for RNA polymerase to access genes and so preventing transcription
what is a operon
.cluster of genes controlled by a promoter which allows for coordinated expression in prokaryotes
key components of operons
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
what is the lac operon
.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
what does the lacI regulatory gene do
codes for the repressor protein that inhibits the lac operon activity
lacZ
.enzyme- beta-galactosidase
.breaks down lactose into glucose and galactose
lacY
enzyme- lactose permease
.transports lactose into the cell
lacA
enzyme- transacetylase
.modifies lactose or its by products
how does the lac operon function when lactose is absent
.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
how does the lac operon function when lactose is present
.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
how is the lac operon regulated by glucose
.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
how is pre-mRNA processed
.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
how does mRNA degradation rate effect the rate of translation
.mRNA degrades slowly is more stable and lasts longer
.this increases translation and protein synthesis
how do inhibitory proteins affect the rate of translation
.they bind to mRNA preventing it from attaching to ribosomes
.this decreases the translation and protein synthesis
how do initiation factors affect the rate of translation
they help mRNA bind to ribosomes initiating translation and so increasing protein synthesis
how do protein kinases modify proteins
.they add phosphate groups to proteins via phosphorylation
.this changes the proteins tertiary structure
.this often activates enzymes
(regulated via cAMP)
what are some examples of post-translational modification
.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)
what is a body plan
.structured arrangement of an organism’s parts
.determined by genetics and developmental factors
what are homeobox genes
group of regulatory genes with a conserved DNA sequence that guides the development of body plans
what is a homeobox sequence
.highly conserved DNA sequence found in homeobox genes that is used for the development of an organism’s body plan
what is a hox gene
.set of homeobox gene in animals
.contains homeobox sequences for correcting positioning of body parts
process if how hox genes control development
homeobox sequence encode the homeodomain
.homeodomain operates as a transcription factor and binds to DNA switching developmental genes on or off
what things can hox genes control
.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
why are homeobox genes so conserved
.mutations can alter the body plan
.genes would be affected within the homeobox gene
.this makes mutations lethal and selected against
how apoptosis and mitosis shape the body plan
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
how do developmental genes respond to internal stimuli
.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
how do developmental genes respond to external stimuli
.regulatory genes respond to changes like temp or light intensity
e.g. lack of nutrients = trigger cell division
