The control of gene expression 8 Flashcards
what is a mutation
an abnormal change in the DNA base sequence
what are the potential impacts of a mutation
different amino acids are coded for, so a different base sequence is present, meaning a different protein structure when the polypeptide chain assembles
highlight it says potential, as the genetic code is degenerate.
what are the main types of gene mutations
point mutations and frame shifts
what are point mutations
a mutation that just affects one nucleotide/base
what is a chromosome mutation
changes in the structure or number of whole chromosomes
what are the two types of chromosome mutations
changes in whole sets of chromosomes
changes in individual chromosomes
A mutation can lead to the production of a non-functional enzyme. Explain how (6)
Change in base sequence of DNA
So a change in the primary structure/amino acid sequence of the enzyme
SO theres a change in hydrogen/ionic /disulfide bonds
So theres a change in the tertiary structure
Theres changes in the active site of the enzyme, meaning it is no longer complementry to its substrate, and no E-S complexes form
What does totipotent mean
when a cell has the potential to become any cell
What are stem cells
undifferentiated dividing cells
What are some sources of stem cells in mammals
inner cell mass of a blastocyst
fetal stem cells
bone marrow
what does pluripotent mean
cells that can become almost any kind of cell
what does multipotent mean
cells can differentiate into a limited number of specialised cells
what does unipotent mean
cells that can only differentiate into a single cell type
what is an induced pluripotent stem cell
a type of pluripotent cell that is developed from a unipotent cell
Recall the levels of protein structure
Primary structure - a specific sequence of amino acids joined together by peptide bonds to form a polypeptide chain
Secondary structure - hydrogen bonds form between different amino acids, forming either a beta pleated sheet or an alpha helix
Tertiary structure - Disulfide bridges, ionic bonds, hydrogen bonds and hydrophobic/hydrophilic interactions form between R groups of amino acids, pulling the structure together
Quaternary structure - two or more polypeptide chains join together through hydrogen bonds
Translation steps
Translation
mRNA leaves nucleus through a nuclear pore
mRNA arrives at ribosome and binds to it at the start codon
tRNA molecules brings a specific amino acid to the ribosome
The anticodon on the tRNA is complementary to the codon on the mRNA
Peptide bonds will form between adjacent amino acids
Two tRNA molecules can enter the ribosome at a time
Multiple peptide bonds between multiple amino acids lead to the formation of a polypeptide chain
Transcription steps
Transcription
DNA helicase unwinds and unzips the DNA double helix into two strands by breaking the hydrogen bonds between complementary organic base pairs, and only one called the coding strand is used
Free, activated RNA nucleotides form temporary hydrogen bonds to complementary base pairs (uracil to adenine, cytosine to guanine)
RNA polymerase catalyses phosphodiester bonds between RNA nucleotides that are adjacent to each other, forming a mRNA molecule
mRNA detaches from the coding strand, and the DNA double helix rewinds itself
what is the difference between cell specialisation and cell differentiation
specialisation is the cell being changed to only able to carry out specific functions, where are differentiation is the process of the cell changing
Is cell specialisation reversible or irreversible
irreversible
Explain how oestrogen affects gene transcription
Oestrogen is lipid soluble and so cross the cell membrane via simple diffusion
Oestrogen binds to receptor on transcription factor, changing the tertiary structure
This allows the polymerase enzyme to attach to the beginning of the DNA double helix strands (promoter region)
ADD MORE
Outline the effect of oestrogen on transcription factors
Oestrogen is non-polar and therefore lipid soluble. It diffuses simply across the phospholipid bilayer.
Oestrogen binds to the receptor on the transcription factor, causing it to change in tertiary structure
Due to this change in tertiary structure, the transcription factor is now complementary to the promoter region of the target gene.
The transcription factor then binds to the promoter region at the start of the gene, activating RNA polymerase to start transcribing the gene.
if DNA is more tightly wrapped around the histone proteins, is the gene turned on or off. Why?
Off
Transcription factors cannot access the gene
if DNA is less tightly wrapped around the histone proteins, is the gene turned on or off. Why?
On
Transcription factors can access the gene
what is acetylation
the addition of an acetyl group to histone proteins from coenzyme A
what is deacetylation
the removal of an acetyl group off of a histone by coenzyme A
what is methylation
the addition of a methyl group
how does methylation work (theres two ways)
attracts proteins that cause deacetylation of histones
blocks promoter regions, preveenting transcription factors
acetylation results in a gene being…
expressed
methylation results in a gene being
not expressed
what is epigenetics
heritable changes in gene function, without changes to the base sequence of DNA.
describe the structure of a nucleosome
DNA wrapped around histone proteins, either tightly or loosely
what are the two genes involved in mutations that lead to cancer
the proto oncogene and the tumor suppressor gene
what are the two types of tumor
benign and malignant
features of benign tumors
features of malignant tumors
how can mutations of the DNA base sequence lead to a non-functional enzyme
change in the DNA base sequence
there’s a change in the amino acid sequence
so a different tertiary structure due to different positions of hydrogen/ionic/disulphide bonds
so a change in the shape of the active site
so substrate can no longer for E-S complexes
whats a way to remember what methylation and acetylation do for epigenetics
InT: IM DNA/DAH
INhibit Transcription by Increased Methylation of the DNA or Decreased Acetylation of associated Histones
what is a tumour
a mass of cells created by uncontrolled cell division
what is metastasis
cells breaking off of a tumour and travelling elsewhere in the body via the blood stream
which tumours, benign or malignant, undergo metastasis
malignant
What is the protooncogene and what does it do
a normal genen that codes for a protein that stimulates cell division
what makes a protooncogene become an oncogene, and what does this mean
a mutation will cause the proto oncogene to become an oncogene
the mutation will change the amino acid sequence of the protein it codes for
this creation results in the protein speeding up cell division too much, leading to a tumour growing
what is the tumour supressing gene and what does it do
a gene that has the normal function of coding for a protein that slows down the rate of cell division
what makes a tumour suppressor gene become unworking, and what does this mean
a mutation in the gene, meaning the protein that it codes for may not be able to slow down the rate of cell division
this increases the risk of uncontrolled cell division and a tumour growing
The amount of methylation of tumour suppressor genes and oncogenes has an impact on cancer risk and implications for the design of cancer treatments.
Discuss how this might occur.
Increased methylation of an oncogene will inhibit transcription of this gene.
This could prevent uncontrolled cell division and tumour formation.
Increased methylation of a normal tumour suppressor gene will inhibit transcription of this gene.
This could lead to uncontrolled cell division and tumour formation.
Describe how alterations to tumour suppressor genes can lead to the development of tumours (3)
increased methylation of tumour suppressor genes or a mutation in the tumour suppressor gene
means that the gene is not transcribed and the amino acid sequence is altered
so the protein doesnt work
so uncontrolled cell division occurs
A type of malignant cell divides every 8 hours.
Starting with one of these cells, how many tumour cells will be present after 4 weeks? Assume none of these cells will die.
Give your answers in standard form
1.93 x 10^25
672 hours
672/8 = 84 divisions
2^84 = 1.93 x 10^25
what does RNAi do
translation of the mRNA produced by target genes can be inhibited
how does RNAi work
the double stranded RNA is broken up by an enzyme into small interfering RNA (siRNA) via hydrolysis
One of the strands on siRNA combines with the enzyme
the siRNA strand on the enzyme pairs with complementary bases of a mRNA strand
the enzyme cuts the mRNA that the siRNA has binded to into smaller sections
so the mRNA strand is destroyed
what changes can occur during transcription to mRNA
mutations
epigenetic changes -> is the gene accessible
are transcription factors activated -> e.g. by oestrogen
what changes can occur during translation to mRNA
siRNA (small interferring RNA)
what does hypermethylation mean
adding more methyl groups, turning the gene off
what does hypomethylation mean
removing methyl groups, turning the gene on
what is a genome
all the DNA in a cell organism
what is the sequencing of a genome
sequencing a genome involves working out the entire DNA base sequence for a cell organism
what is a cellular proteome
all the proteins producing by the genome in a given cell type
what is a complete proteome
all the proteins produced by the genome in the whole organism
what is a proteome
all the proteins produced by the genome
what is the importance of recombinant DNA technology
a lot of human diseases are caused by an individual lacking/being unable to produce a particular themselves
e.g. insulin
what does it mean if a gene is in VIVO
the gene is transferred into a host cell using a vector to be cloned
recombinant DNA technology meaning
taking DNA from two sources and combining them
what are the steps to IN VIVO cloning (a gene in VIVO)
1 - isolation -> isolating the gene of interest
2 - insertion -> inserting gene OI into a vector
3 - transformation -> the plasmid transforms the bacterium
4 & 5 - identification and growth/cloning
we can call a bacterium that uptook the plasmid that has the new DNA in it
transformed and transgenic
what is a way of isolating a desired gene
using restriction endonucleases to cut out the fragment of DNA containing the desired gene of interest from the DNA
what does it means if a gene is in VITRO
the gene is copied using a method called PCR and is performed in a lab
what do we call a bacteria that has taken up the plasmid but shows no sign of containing the desired gene
transformed, and NOT transgenic
what are the 3 ways to isolate a gene
using reverse transcriptase
using restriction endonucleases
using a gene machine to create the gene
outline how we isolate a gene using reverse transcriptase
desired gene on the mRNA strand acts as a template as single stranded complementary copies of DNA (cDNA) is formed using reverse transcriptase
cDNA is isolated by the hydrolysis of the mRNA strand
DNA polymerase then combines complementary DNA nucleotides to the cDNA to form a double stranded DNA molecule that contains the code for the gene
outline how we isolate a gene using restriction endonucleases
specific endonuclease cuts into a specific point on the DNA strand
plasmid is removed form bacterium
same endonuclease that was used to cut the DNA fragment cuts the plasmid open
the ends of the DNA and the gene are joined together by DNA ligase via phosphodiester bonds, sometimes this is called annealing
why is it that each restriction endonuclease will cut DNA at a specific base sequence
has a specific tertiary structure, so a specific active site that is complementary to the shape of a specific DNA base sequence
describe how restriction endonuclease and DNA ligase are used to insert a gene into a plasmid
restriction endonuclease cuts plasmid
ligase joins gene/DNA and plasmid together
outline how we isolate a gene using a gene machine
a protein is used and worked ut backwards to the mRNA code to the DNA code
machine starts by using free nucleotides to make lots of short, single stranded DNA molecules called oligonucleotides
what are marker genes and what do they do
genes that are used to detect cells or organisms that have been successfully genetically modified
outline the PCR cycle
heat to 95°C, as this will break the hydrogen bonds between DNA strands so that the strands separate
reduce temperature to 55°C, as this will allows DNA primers to hydrogen bond with their specific complementary DNA bases on the DNA strands
heat back up to 72°C, as this will allow DNA nucleotides to be added to each primer via complementary base pairing with the template strand, joined together by DNA polymerase
what are the ‘ingredients’ for a PCR tube
DNA sample, DNA polymerase, free DNA nucleotides, DNA primers
how can we increase the permeability of a cell membrane
heat it, or increase concentration of Ca2+ ions
