6.1.1 Cellular Control Flashcards
Define Mutation
a change in the sequence of bases in DNA
How does a change in a DNA Sequence occur?
substitution, deletion, insertion of 1 or more nucleotides (or base pairs)
Define Point mutation
a mutation affecting only one nucleotide in a gene sequence
Define Substitution
a mutation where 1 or more nucleotides are substituted for another in a DNA strand
Define Deletion
a mutation where one or more nucleotides are deleted and lost from the DNA strand
Define insertion
a mutation where one or more extra nucleotides are inserted to the DNA strand
Define frame shift mutation
the insertion or deletion of 1 or more nucleotides which leads to frame-shift mutation
- shifts reading frame of the sequence of bases/amino acids as it will change every successive codon from the point of mutation
- this alters the tertiary structure of the protein
Define Silent mutation
a substitution mutation that changes a single DNA nucleotide but does not affect the sequence of amino acids that make up the gene’s proteins
Define Nonsense mutation
a substitution mutation of a single base pair that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid
Define missense mutation
a substitution mutation that changes the nucleotide sequence which changes the amino acid and alters the properties of the protein
- two types : loss of function, gain of function
Define Gene mutation
a change in the DNA sequence of a single gene
Define Chromosome mutation
a change in the number of chromosomes or gene arrangement of chromosomes
Why can a change in the sequence of nucleotides of a gene affect the function of the protein produced from that gene?
- the sequence of nucleotides could be mutated to a new sequence that codes for a different amino acid triplet
- therefore a different protein = the new protein won’t carry out the same functions
Describe how a mutation can have a neutral effect? give an example
- mutations can be silent - causing no change to proteins
e.g. a mutation of a sequence of nucleotides can lead to no change in sequence of amino acids as the genetic code is degenerate - no effect on phenotype of an organism bc normally fuctioning proteins are still synthesised
Describe how a mutation can have a harmful effect? give an example
when the phenotype of an organism is affected in a negative way - bc proteins are no longer synthesised or proteins synthesised are non-functional
e.g. nonsense mutations
Describe how a mutation can have a beneficial effect? give an example
when a protein is synthesised that results in a new and useful characteristic
e.g. a mutation in a protein present in the cell surface membranes of human cells -HIV cannot bind and enter
What are the 3 types of mutagen? give an example of each
- Physical mutagens - x-rays
- Chemical mutagens - deaminating agents
- Biological agents - viruses, alkylating agents
Define mutagen
a chemical/physical/biological agent which causes mutations
What are the 4 types of chromosome mutation?
- deletion - section of chromome breaks off and is lost within cell
- duplication - sections of dna duplicated on chromosome
- translocation - section of 1 chromosome breaks odd and joins another non-homologous chromosome
- inversion - section of chromosome breaks off, is reversed and joins back onto chromosome
Explain the possible effects of substitution mutation.
(no effect, damaging, beneficial)
- no effect - no effect on phenotype bc normally functioning proteins still synthesised
- damaging - phenotype affected in negative way bc proteins no longer synthesised/proteins synthesised non-functional
- beneficial - protein synthesised results in new and useful characteristic in phenotype
Explain possible effects of insertion or deletion mutations
- frameshift mutation
- move shift triplet code
- distrupts reading of triplet codon
- changes every successive codon from point of mutation
- changes protein structure
Define gene expression
- genetic information in DNA converted into instructions for making proteins
Define epigenetics
- control of gene expression by modification of DNA
What are the four levels at which genes (or proteins) are regulated?
- Transcriptional - genes turned on and off
e.g. lac operon + chromatin remodelling - Post-transcriptional - mRNA can be modified to regulate translation and types of proteins produced
e.g. RNA processing - Translational - gene translation can be stopped and started
e.g. degradation of mRNA - post-translational - proteins can be modified after synthesis to change their functions
e.g. folding/shortening proteins
What is trascription?
turning genes on and off
e.g. chromatin remodelling and lac operon
Define - chromatin , heterochromatin and euchromatin
- chromatin - uncondensed DNA wound around histone proteins (+ve charge)
- heterochromatin - tightly wound DNA causing chromosomes to be visible during cell division
- euchromatin - loosely wound DNA
Why is gene expression not possible in heterochromatin but is possible in euchromatin?
- when DNA tightly wound (heterochromatin) transcription not possible as RNA polymerase cant access the gene
- in euchromatin DNA loosely wound so RNA polymerase can access gene and do trancription
How can histone modification (increase or decrease packing degree) affect gene expression?
- histones can be modified to increase or decrease degree of packing
- if packing degree decreaeses DNA can be transcribed
- if packing degree increaes DNA cannot be transcribed.
is chromatin remodelling a eukaryote or prokaryote example of …..?
- chromatin remodelling is a eukaryote example of transcription
- in eukaryotes …….. …… control transcription of genes.
- factors stopping transcription are …..
- ## factors starting trascription are …….
- 1 transcription factors
- 2 repressors
- 3 activators
Define operon
- a group of genes controlled by the same regulatory mechanism and are expressed at the same time
is the lac operon a eukaryote or prokaryote example of …..?
- prokaryote
- example of transcription
Draw a diagram to show the lac operon and its associated regulatory gene.
What is the role of the regulatory gene and the name of the one associated with the lac operon?
- Regulatory gene - codes for a repressor protein (that prevents the transcription of the structural genes in absence of lactose)
- lac I
What does the repressor protein do?
- coded for by a regulator gene
- repressor protein: prevents transcription of the structural genes in the absence of lactose
describe the roles of:
- regulatory gene
- structural genes
- operator region
- promotor region
of lac operon for metabolism of lactose
- repressor protein bind to the operator
- repressor protein blocks RNA polymerase binding site on promoter
- RNA polymerase cannot bind to DNA and start transcription of structural genes
OR - RNA polymerase binds to the promotor region which releases lactose/repressor protein complex from the operator region allowing transcription to begin
How does the lac operon work when lactose is absent from growth medium but glucose is present?
- regulatory gene Lac I codes for repressor protein which binds to the operator
- No lactose to bind to the repressor protein and so doesnt change proteins shape
- RNA polymerase cannot bind to promoter region due to shape of repressor protein blocking promoter
- transcription of structural genes cant occur
What are structural genes?
- give the 3 structural genes of the lac operon
- structural genes: proteins/enzymes which are not involved in DNA regulation
- lac Z
- lac Y
- lac A
- all produce enzymes to metabolise glucose
How does the lac operon work when glucose is absent from growth medium but lactose is present?
- Lac I codes for repressor protein which binds to operator
- lactose binds to repressor protein and causes a change in the proteins shape
- repressor protein is released from the operator as it can no longer bind to it
- unblocked promoter so RNA polymerase can bind to promoter and transcribes 3 structural proteins
- enzymes synthesised to metabolise lactose
What binds to the promotor?
- section of DNA sequence where RNA POLYMERASE binds to
What binds to the operator?
- section of DNA sequence where repressor protein binds to
What is the role of cAMP in lac operon
- cAMP increases rate of transcription
- cAMP receptor protein binding to RNA polymerase
What is post-transcriptional gene expression?
primary mRNA made in transcription is modified to regulate translation and types of proteins produced
e.g. rna processing
Why is mRNA in eukaryotic cells edited?
- eukaryotic DNA contains introns and extrons
- introns are edited out of DNA
Define intron
- regions that do not code for proteins
Define exons
regions that do code for proteins
What is pre-mRNA
the product of transcription that contains introns and exons
What is mature mRNA?
modified pre-mRNA that can bind to a ribosome and code for proteins
Define RNA processing
- preparing RNA to leave nucleus
Define RNA editing
- the nucleotide sequence of mRNA molecules is changed through base addition, deletion, substitution
Describe the 4 steps on how pre-mRNA is modifiedn to produce mature mRNA
- RNA SPLICING - introns are removed from from mRNA
- ADD CAP TO 5’ END - (cap is modified nucleotide)
- ADD TAIL TO 3’ END - (tail is a long chain of adenine nucleotides)
- tail + cap help: stabilise mRNA and delay degradation in cytoplasm - further mRNA editing through substitution, insertion and deletion
Where is pre-mRNA modified (post-transcription)?
in the nucleus
What is the benefit of mRNA modification (post-transcription)?
make different versions of mRNA to => synthesise different proteins with different functions
What is translational control?
regulates protein synthesis
What are the 3 mechanisms in translational control which regulate translation?
2 - down regulate translation (dont want translation)
1- does do translation
Down regulate translation via:
1. degradation of mRNA - eliminates mRNA - no mRNA = no translation
2. inhibiatory proteins bind to mRNA - prevents mRNA binding to ribosomes = prevents protein synthesis
Translation does happen:
3. activate initiation factors
help mRNA bind to ribosomes
What is the role of protein kinases in regulating gene expression/protein activity
protein kinases enzymes:
- catalyse adding of PO4 group to proteins
- changes tertiary structure and therefore function of the protein
What is post translational control?
modification of proteins that have been synthesised
What are the 4 ways which proteins can be modified to do post translational control?
- Adding non-protein groups - e.g. carbohydrate chains,lipids, phosphates
- Modifiy amino acids and therefore the formation of bonds - e.g. modify AA to form disulfide bridges (add sulfate)
- Fold/shorten proteins - affects tertiary (3d structure)/quaternary (combination of subunits)
- Modification by cAMP - e.g. (1) cAMP + CRP - bind to RNA polymerase and increase rate of transcription of structural genes
e.g. (2) cAMP + kinases -> activate other enzymes/proteins
Define homeobox gene
- a group of genes which all contain a homeobox
Define body plan
the general structure of an organism
Define morphogenesis
the regulation of the pattern of anatomical development
Define homeodomain
part of a protein which binds to DNA and switches genes on and off
Define hox gene
the group of homeobox genes that are only present in animals
What are the 3 kindgoms which all have very similar homeobox genes?
- animalia
- plants
- fungi
How are homeobox genes similar across life and how they differ?
- homeobox is section of DNA that is 180 base pairs long and codes for part of protein 60 amino acids long - it is highly conserved
- differ: mutations
What is meant by highly conserved?
- one that has remained relatively unchanged
What is the role of Hox genes in controlling the body plan of animals?
- responsible for correct positioning of body parts
How do hox genes control development? (5 steps)
- homeobox sequences of hox gene code for a part of the protein called the homeodomain
- homeodomain binds to specific sites on DNA -
- enables protein to act as transcription factor either activate or repress transcription
- homeodomain binds at start of developmental genes so alters production of proteins involved in body plan development
What are 3 function types of homeobox genes and give examples for each
- symmetry - e.g. bilateral symmetry
- mitosis - cell division and proliferation e.g. increase number of cells leading to growth
- apoptosis - cell death and also release chemical signals which stimulate mitosis - leads to remodelling of tissue e.g. digits on hands and feet
Define apoptosis
programmed cell death
What is the process of apoptosis
- removes unwanted cells and tissues to shape different body parts
- cells undergoing apoptosis can also release chemical signals which stimulate mitosis and cell proliferation leading to remodelling of tissues
How is apoptosis controlled?
- hox genes control apoptosis
- increased transcription of genes responsible for apoptosis
What is the role of mitosis in growth and development?
- results in cell division and proliferation
- increases number of cells leading to growth
How can apoptosis be used during growth and development?
- releases chemical signals to stimulate mitosis
What are factors that affect expression of regulatory genes?
environmental:
- internal - stress
- external - changes in temp/light intensity
Define stress in relation to homeostasis and describe factors that may influence the rate of mitosis or apoptosis?
stress - condition produced when homeostatic balance within an organism is upset
factors: - change in temperature or intensity of light
