A2 - the control of gene expression

what do gene mutations do

change base sequence of DNA

gene mutations can arise _____________

spontaneously

define mutagenic agent

increases the rate of gene mutation

examples of mutagenic agents

X-rays, viruses, carcinogens

what are the 4 types of gene mutations?

substitution, addition, deletion and inversion

What is a frameshift mutation?

insertions or deletions of DNA, causes reading frame to be moved.

what could gene mutations code for in DNA

stop or start codons

define stem cell

Undifferentiated cell with the potential to become specialised

what can stem cells do

differentiate into other types of cells

what is a totipotent cell

can differentiation into every cell type

what is a pluripotent cell

can differentiate into most cell types

what is a multipotent cell

can differentiate into a limited number of cell types

what is a unipotent cell

can differentiate into just one cell type

what are some medical treatments using stem cells

tissue regen, nerve cells. blood cells

risks of stem cell treatments

ethics, no guarantee of success

benefits of stem cell treatments

replaces cells affected by disease, patient specific treatments

what is a transcription factor

a protein

where do transcription factors move from

from cytoplasm to nucleus

what do transcription factors do

bind to a specific point on DNA which stimulates transcription

what also binds with transcription factors

RNA polymerase

define nucleosome

DNA wrapped around histone proteins

how closely DNA and histones are packed together affects _____________

transcription

describe how oestrogen can initiate transcription

- oestrogen diffuses through phospholipid bilayer

- binds to receptor on transcription factor causing change in shape

- now complementary fit to DNA

- TF enters nucleus and binds to DNA along with RNA polymerase

define epigenetics

heritable changes in gene function without changes to base sequence of DNA, caused by changes in the environment

What is methylation of DNA and how does it affect transcription

- adding methyl groups to DNA

- nucleosomes pack more tightly together so prevents TF binding so gene is not transcribed

what is decreased acetylation of associated histones and how does it affect transcription

- increases positive charge of histones

- histones bind DNA more tightly so prevents TF binding

what can translation of mRNA be inhibited by

RNAi (RNA interference)

describe how translation is stopped by small interfering RNA

- enzyme cuts mRNA into siRNA

- one strand of siRNA combines with another enzyme

- siRNA-enzyme complex binds to mRNA via complementary base pairing

- enzyme cuts mRNA so translation stopped

what are some epigenetic modulations

- drugs

- toxic chemicals

- disease exposure

it is ____ to switch on genes if nucleosomes are ________ packed together

hard, tightly

what charge is DNA?

negative

what charge are acetyl groups

positive

how is a tumour formed

uncontrolled cell division

define benign

non-cancerous, doesn't spread

define malignant

cancerous, spreads easily

benign vs malignant tumours

benign: slow growing, well differentiated, normal nuclei, easy to treat

malignant: fast growing, poorly differentiated, dark nuclei, removed by radio/chemotherapy

what is a tumour suppressor gene

slows down or stops mitosis

what is the normal function of tumour suppressor genes

stops cell cycle when damaged DNA detected, causes apoptosis of cells

what is the role of tumour suppressor genes in development of tumours

- mutations alter AA sequence = non functional protein

- increased methylation prevents transcription

- damaged DNA not repaired

what do proto-oncogenes do

stimulate cell division

what role do proto-oncogenes have in development of tumours

- mutation could make them permanently active

- decreased methylation / increased acetylation causes excess transcription

- cell division permanently activated

what do terminator nucleotides do?

prevents further nucleotides from binding

what are primers used for in sequencing projects

attaches to DNA and begins synthesis

what are primers usually labelled with

a radioisotope or fluorescent dye

which fragments move the furthest in the sanger sequencing method

smallest fragments

why do the DNA fragments move different distances in the gel?

they are all different sizes

the transfer of dna fragments from one organism to another

what is recombinant DNA technology

mRNA isolated from cell, mix with DNA nucleotides and reverse transcriptase, cDNA strand produced, DNA polymerase forms second strand of DNA

how can reverse transcriptase be used to produce DNA fragments

cut DNA at specific recognition sites with complementary base pairs, creates sticky ends

how can restriction endonucleases be used to produce DNA fragments

synthesises DNA fragments from scratch

how can the gene machine be used to produce DNA fragments

fragments produced quickly and accurately , free of introns

advantages of using the gene machine

- more mRNA in cell than DNA

- introns removed by splicing

- bacteria cant remove introns

advantages of using mRNA to make DNA fragments rather than restriction enzyme to cut gene from DNA

promotor tells RNA polymerase when to start transcription, terminator tells RNA polymerase when to stop transcription

why are promotor and terminator regions added to DNA fragments in in vivo cloning

vector DNA and DNA fragment cut using same restriction enzyme so they have complementary sticky ends. DNA ligase forms phosphodiester bonds between adjacent nucleotides o sticky ends

explain how DNA fragments are inserted into vectors

carries DNA into host cell e.g. plasmid

what is a vector

host cell membrane must be more permeable. make more permeable by placing host cell into ice cold calcium chloride solution and heat shock mixture

explain how vectors are transformed into host cells

used to identify which cells have the desired gene. they are needed as not all cells will take up the vector and be transformed

what are marker genes and why are they needed

antibiotic resistance, fluorescent protein, enzyme

what are the 3 types of gene markers

polymerase chain reaction

what is PCR

amplification/cloning of DNA fragments

what is PCR used for

DNA fragment, DNA(taq) polymerase, primers and nucleotides

what is in the reaction mixture for PCR

95 degrees C , separated DNA strands by breaking hydrogen bonds

explain the separation step in PCR

55 degrees C , allows primers to bind, forming hydrogen bonds. primer complementary to template DNA. DNA polymerase binds to primer to start synthesis

explain the annealing step in PCR

72 degrees C , DNA polymerase joins complementary nucleotides to exposed bases, forming phosphodiester bonds

explain the DNA strand synthesis step in PCR

- 95 degrees breaks H bonds between double helix

- cool to 55 degrees so primers can bind - annealing

- increase to 72 degrees so taq polymerase can join nucleotides by complementary base pairing

describe PCR in 3 simple steps

inside an organism e.g. bacteria

what is in-vivo cloning

outside an organisms e.g. PCR

what is in-vitro cloning