6.1.1 cellular control Flashcards
mutation
random change in base sequence of DNA
what causes a mumtation
mutagen
examples of mutagens
- tar in tobacco smoke
- ionising radiation
2 classes of mutation
- point mutation
- insertion/deletion (indel)
point/substitution mutation
one base pair replaces another
indel mutation
- one or MORE nucleotides are INSERTED or DELETED from a legnth of DNA
- can cause a frameshift
3 types of point mutation
- silent
- missense
- nonsense
silent mutation
triplet code is changed but due to the degenerate nature of code the same amino acid is still produced
- primary secondary tertairy structure of protein all the same
inversion mutation
- eg tac becomes cat
- affects one amino acid
missense mutation
- change in base triplet resulting in a different amino acid produced
nonsense mutation
- base code becomes a STOP triplet
- truncated protein that wont function
frameshift
- caused by INDEL mutation
- when base pairs are inserted/deleted not in threes, due to the code being NON OVERLAPPING
- all the subseqeuent base triplets are altered; all amino acids are altered
expanding triple nucleotide repeat
- repeating triplet sequence repeats even more
why could silent be harmful?
- could code for RNA that regulates the expression of other genes
- could incorrectly regulate this
exon
coding region of DNA
intron
non coding region of DNA
operon
a group of genes that function as a single transcription unit
transcription factors (eukaryote)
- proteins that act to control which genes are turned ON or OFF
simplified, how do TF work
ACTIVATOR:
- bind to promoter region of gene, aiding RNA polyemerase to bind to transcribe the gene
REPRESSOR:
- binds to gene, BLOCKS rna polymerase from binding
operon
a section of DNA containing a cluster of genes which are controlled by a single promoter
3 parts of the operon (link to lac)
- structural genes: (lac z,y,a)
- control elements: (promoter for RNA p to bind and operator where transcription factors can bind)
- regulatory gene: (lac I) codes for transcription factors
ecoli relation to lactose
- e coli normally respires glucose
- if glucose is absent, and LACTOSE present, it induces the production of:
1. lactose permease
2. beta galactosidase
importance of the fact that e coli can only produce these enzymes when glucose absent and lactose present?
- doesnt waste ATP and amino acids on making proteins they dont need
what codes for lactose permease
lac Y
what codes for beta galactosidase
lacZ
beta-galactosidase purpose
breaks glycosidic bonds; hydrolyses lactose to glucose and galactose
what actually induces the enzymes
LACTOSE (but absence of glucose is needed)
what is the purpose of the lac operon
contains the genes that produce the enzymes needed to respire lactose: lactose permease and beta galactosidase
lac operon structure
DRAW
IPOZYA
1. lac I
2. promoter
3. operator
4. lac z
5. lac y
6. lac a
structural genes
genes that code for proteins NOT INVOLVED in DNA regulation
lac z,y,a
are lac z, y , a involved in DNA regulation ?
NO
lac I
- regulatory gene (codes for proteins involved in DNA regulation)
- codes for a REPRESSOR PROTEIN
operator (lac opeoron)
DNA sequence to which repressor protein binds
promoter (lac operon)
DNA sequence to which RNA polymerase binds
homebox sequence
REGULATORY GENE THAT CONTROLS BODY DEVELOPMENT
- contains 180 base pairs, encoding a 60 amino acid HOMEODOMAIN seqeucne that is part of a protein
- control body development
what does the homeodomain sequence do
- fold into a particular shape and bind to DNA
- act as TRANSCRIPTION FACTORS, switching some genes on and repressing others
homeobox genes highly conserved ; what does that mean
- remained in all descendent species throughout evolutionary history
- little difference between the hbox genes of diff species
HOX genes
- subset of homeobox genes, ONLY FOUND IN ANIMALS, involved in formation og anatomical features in correcet locations of body plan
where are homeobox genes found
animals, plants, fungi
regulatory genes
genes that code for proteins that are involved in DNA repllication
what do homeobox genes also regulate …
-mitosis and apoptosis (responding to internal and external stimuli)
apoptosis defintion
programmed cell death
steps of apoptosis
- enzymes break down the cell cytoskeleton
- cytoplasm becomes dense with tightly packed organelles
- cell surface membrane changes; small protrusions called BLEBS form
- chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments
- the cell breaks into vesiclaes that are ingested by phagocytes
what can apoptosis + mitosis be triggered by
internal and external stimuli, to control rate of growth
apoptosis and mitosis relation
- rate of cell death should = reate of cells produced
1. not enough apoptosis = tumours
2. too much apoptosis = cell loss and degeneration
POST TRANSCRIPTIONAL GENE EXPRESSION in one line
modifying mRNA so it can be translated
primary-mRNA
- contains a mix of introns and extrons; freshly transcribed from the DNA
what enzyme is used in splicing
endonuclease
translational level of gene expression
- regulation of translation (if it happens or no)
lac operon: normal circumstances, glucose present
- regulatory gene Lac I codes for REPRESSOR protein.
- this TRANSCRIPTION FACTOR binds to the OPERATOR
- repressor TF is large so BLOCKS the promoter from being bounded to the RNA polymerase
- therefore transcription of the structural genes (z,y,a) can’t occur as ur respiring glucose instead
lac operon: glucose NOT present
- regulatory gene lac I codes for REPRESSOR protein
- LACTOSE binds to the transcription factor REPRESSOR PROTEIN, causing a confirmational change of the REPRESSOR.
- Repressore therefore cannot bind to the operator
- promoter is free, RNA polymerase binds, lac zya STRUCTURAL PROTEINS are coded for
- beta galactosidase and lactose permease enzymes are coded for and lactose can be respired
what DNA contains introns
ONLY EUKARYOTES, not prokaryotes
splicing; post transcriptional control
- primary mRNA contains introns and extrons
- need to be MODIFIED to REMOVE introns and JOIN exons
- produces mature mRNA ready for translation
example of post translational gene regulation
- activation of proteins
- eg phosphorylation of enzymes BY CAMP
How does cAMP work in post translational gene regulation
- HORMONE, binds to receptor on CSM of the target cell
- confrimational change in shape of receptor, which activates a G protein
- G protein activates ADENYL CYCLASE ENZYMES
- CATALYSES conversion of ATP to cAMP
- cAMP binds to PKA to activates
- Activated PKA catalyses the phosphorylation of various proteins (so enzymes are activated), hydrolysing ATP in the process.
- PKA can also phosphorylate another protein wchich can enter the nucleus and act as a transcription factor
how to homebox genees actually work
- homedomain sequence
- codes for TRANSCRIPTION FACTORS that can activate or suppress gene expression WHEN NEEDED during development of a zygote
DNA, mRNA, tRNA relations
DNA=> mRNA is complementary but U instead of T => tRNA is complementary (and same as DNA but U instead of T)
is meiosis involved in body plan development
NO
cell cycle order
G1
S
G2
Mitosis (PMAT)
Cytokinesis
why are genes not expressed during cell division
HETEROCHROMATIN
- chromasomes are vv tightly wound around histones
euchromatin
chromosomes wound less tighlty around histones; genes can be expressed
explain how a mutation could have no effect on function of protein (4)
- degenrate triplet codes
- same amino acid seqeucne
- chemically simialr AA produced; doenst alter shape of protein
- mutation in an intron
explain how a mutation could have an affect on function of protein(4)
- indel mutation = frame shift
- all codons after affected
- different sequence of amino acids
- different tertiary structure
explain IN DETAIL (5) the change in triplet on change in primary structure; LINKING TO TRANSLATION
- diff base sequence of DNA
- diff mRNA triplet
- diff tRNA ANTICODN
- tRNA brings a different amino acid
- different primary structure of amino acids
why light microscope (4)
- mag within range
- smaller organelles not visible
- colour
- wide field of view
uses of mitosis (4)
- growth and repari of tissues
- body plan
- clinal expansion
- asexual reproduction
explain how transcription factors work (4)
- hormone enters cell
- binds with the transcription factor to activate it
- TF binds to promoter
- allows RNA polymerase to bind, genes can be expressed
describe post transcriptional regulation (5)
- primary mRNA modified
- removal of introns and joining of exons
- ALTERNATIVE SPLICING CAN PRODUCE VERSIONS OF MRNA THAT CODES FOR ANOTHER PROTEIN
- cAMP phosphorylates (activates) enzyme
- binding may alter shape
ROLE OF camp in post translational regulation (2)
- activates PKA which activates the protein by phosphorylation
- the biding may alter the shape of the protein
what makes galactose a good respiratory substance (3)
- polar OH groups = soluble
- soluble so can move/be transported
- bonds contain energy; can be broken
why does lactose need lactose permease? (2)
- too large
- to fit between phospholipids
why use x animal for investigations in body plan? (2)
- cheap
- rapid reproduction
examples of molecules that signal apoptosis (3)
- cytokines
- hormones
- nitric oxide
describe how failure of hox gene means fingers stick together? (3)
- correct transcription factor is not produced
- molecules signalling apoptosis (hormones etc) not produced
- apoptosis not induced
Explain why some regions of DNA can be described as ‘non-coding’ (4)
- mRNA modified
- splicing; introns removed so aren’t in mature mRNA
- are not translated
why is theremuch more variation in non-coding DNA?
not selected against; doesn’t affect survival
is cAMP a protein
no
RNA vs DNA polyemrase (4)
RNA
- used in transcription
- to produce mrNA
- one strand formed
DNA
- used in DNA replication
- 2 strands formed
- before mitosis
state what is meant by a homeobox gene (2)
- regulatory gene
- 180 base pairs ( codes for homeobox sequence)
- codes for TRANSCRIPTION FACTORS that control anatomical body plan
why are homeobox genes highly conserved (4)
- they are extremely important
- would alter body plan
- would affect many other genes
- likely to have LETHAL effects so be selected against
why are stop codons described as such
don’t code for an amino acid
why is yogurt containing bacteria safe for lactose intolerant people to eat? (2)
- bacteria respire the lactose anaerbocially
- produce lactic acid
first thing homebox genes do
head tail orientation
difference between apoptosis and necrosis (3)
- apoptosis is active programmed cell death
- necrosis is passive cell death caused by environmental factors ; trauma
- a = regulated, n= unregulated
- a = no inflammation or damage to surrounding tissues , n = yes damage
how does mutation lead to a truncated protein ? (4)
- nonsense point mutation
- base changed, stop codon; no amino acid coded for
- translation termianted
- no aa added thereafter
why is the genetic code described as universal?
- same 4 nitrogenous DNA bases (a,t,c,g) in all species
- same triplet codes for same amino acid in all species
how do hox control mitosis
- daughter cell has full genome
- daughter cell a clone of adult
describe apoptosis
- enzymes break down the cell cytoskeleton
- cytoplasm becomes dense with tightly packed organelles
- CSM changes and blebs form
- chromatin condenses, nuclear envelope breaks, DNA breaks into fragments
- cell breaks into vesicles that are phagocytosed
