Dr Barnes Flashcards
What were the results of Mendel’s experiment?
Mendelian laws of inheritance
- Segregation - Independent assortment - Dominance
What were the results of DeVries, Correns and Tshermaks experiment?
- “Factors” transmitted from generation to generation influence certain traits
- “Heredity determinants” stay the same from generation to generation- Must be some sort of genetic material
What properties does genetic material have to have?
- Replication of information
- Storage of information
- Expression of information
- Variation by mutation
What was Mieschers experiment?
Studied the chemical composition of the cell nucleus of white blood cells from pus-covered bandages
What were the results of Mieschers experiment?
Found a substance he called nuclein (DNA)
- Could not be a protein as no sulphur and not digested by pepsin protease - Found it contained H,C,O, P
What was Flemmings experiment?
Studied chromosomes of salamander cells to find the stages of cell division
What were the results of Flemmings experiment?
- Discovered chromatin (fibrous structure in the nucleus, easily stained)
- Postulated chromatin becomes chromosomes at mitotic division
- Deduced chromosomes move in mitosis, allowing precise division
- Postulated chromatin becomes chromosomes at mitotic division
What were the results of Sutton and Boveris experiments?
- Stable chromosome structure kept through generations
- Different combinations causes variation
- Sutton-Boveri chromosome theory of inheritance: Chromosomes required for embryonic development and carry Mendels factors
What was Morgans experiment?
Found Drosophila with white eyes, caused by recessive mutation. Linked this to an unusual chromosome composition -> Genes carried on chromosomes
What was Garrods experiment?
Noticed Alkaptonuria (Disorder characterised with black urine) ran in families and analysed its inheritance
What were the results of Garrods experiment?
- Linked human disease to Mendelian inheritance and disorders to metabolic defects
- Proposed diseases were inborn errors of metabolism and there are differences in metabolism between healthy individuals
What were the results of Beadle and Tatums experiment?
Established the one gene-one enzyme hypothesis
How are ascospores grouped?
In asci: the eight products of a single meiosis
What was the pathway Beadle and Tatum studied?
Niacin production
What is minimal growth media?
Media which contains only the nutrients an organism cannot synthesise for itself
What was the method used for Beadle and Tatums experiment?
- Generate mutations in the DNA of individual cells with X-rays
- Generated a series of auxotrophic mutants and seed if they could grow in minimal growth media
What are auxotrophic mutants?
Mutants unable to synthesise essential compounds
What was the method used for Griffiths experiment?
- Kill S bacteria with heat and see if infection occurs
- Inject R bacteria and dead S bacteria into mice and see if infection occurs and if bacteria have a polysaccharide coat
What were the results of Griffiths experiment?
- Realised hereditary material could be passed on by bacteria
- Transforming principle
What was the purpose of Avery, MacLeod and McCarthys experiment?
Find out which molecules were responsible for the transformation that Griffith observed
What was the method used for Avery, MacLeod and McCarthys experiment?
- Systematically destroyed each component of the S strain extract using enzymes
- Combined with live R bacteria to test for transformation
What was the result of Avery, MacLeod and McCarthys experiment?
The molecule taken up is DNA
What was the purpose of Hershey and Chases experiment?
Finding out what component of a bacteriophage is injected into bacteria
What was the method used for Hershey and Chases experiment?
- Label bacteriophage DNA or protein with a radioactive isotope
- Infect unlabelled bacteria with radioactive phage
- Separate phage ghosts from infected bacteria
- Test bacteria and phage ghosts for radioactivity
What was the result of Hershey and Chases experiment?
Worked out bacteriophage DNA injected into bacteria
What did Kossel do in 1878?
Identified the different nucleobases in nucleic acids
What did Levene do in 1929?
Show how nucleotides make up DNA
What was the method used for Chargaffs experiment?
Used paper chromatography to separate and isolate the nucleobase components of DNA from a number of species
What were the results of Chargaffs experiment?
Worked out:
- %A = %T and %G = %C - %Purines = %Pyrimidines - %AT =/= %GC
What were the results of Wilkins and Franklins study of DNA structure?
Worked out DNA had:
- Helix - Repeating, even structure - A distance of 3.5nm for one turn
What were the main features of Watson and Cricks DNA model?
- A-T and G-C hydrogen-bonded base pairs
- Antiparallel strands
- Right-handed double helix
- One helical turn every 10.5bp
- Major and minor grooves
What was the method used for Meselson and Stahls experiment?
- Grow bacteria in media containing 15N to make heavy DNA
- Transfer to media containing 14N to form new light DNA
- Separate heavy and light molecules by ultracentrifugation
What was the result of Meselson and Stahls experiment?
Worked out DNA uses semi-conservative replication
What were the conclusions of Cairns experiment?
- Confirmation of the semi-conservative model of DNA replication
- A single origin of replication in E.coli
- Two replication forks, moving in opposite directions around the circular chromosome
- A single origin of replication in E.coli
What was the method used for Kornbergs experiment?
Separated the proteins in a bacterial cell extract by their electric charge in the hopes of separating polymerase from the other proteins
What were the conclusions of Kornbergs experiment?
- All four nucleotides and Mg2+ (cofactor for DNA polymerase) are required for DNA synthesis
- A free 3’ end to add new nucleotides onto is required: replication proceeds 5’ to 3’
What is the function of Helicase in DNA replication?
Breaks the hydrogen bonds between the two strands so the DNA can unwind into two strands at the replication fork
What is the function of single-strand binding proteins in DNA replication?
Prevent the separated strands from joining together again by binding to the separated strands and stabilising them
What are Okazaki fragments?
The pieces of DNA that are stuck together to make up the lagging strand of replication
What are telomeres?
Short DNA sequences that are repeated at the ends of the chromosomes so that they can be lost without any genetic material being lost
What is the difference between replication at the leading and lagging strands?
The leading strand only has one polymerase as it goes from the start to the replication fork. The lagging strand has lots of polymerases as it goes from the replication fork to the start so as the replication for moves up another polymerase needs to synthesise the new exposed sections
What does it mean when a gene is actively expressed?
Its product is being transcribed and translated
Why is gene regulation needed?
- To avoid wasting energy and resources
- To avoid chaos by only making needed proteins
- To allow adaptation to the environment
What does constitutive expression mean?
The gene is always expressed
What are housekeeping genes?
Genes that are required for basic cell function and are constitutively expressed
What does facultative/responsive/adaptive expression mean?
Genes switched on and off in response to certain stimuli
What are inducible/repressible genes?
Genes that are switched on or off respectively depending on the situation
What is fine gene control?
Instant alteration of critical enzymes
What is coarse gene control?
Long-term changes; positive or negative gene regulation. Amounts of proteins are altered
What is allosterism?
When an enzyme contains an allosteric site in addition to an active site so an inhibitor can bind and modify the active site
What is feedback inhibition?
When reaction products interact with the active site, preventing further substrate binding
How are operons structured in bacteria?
-Several protein-coding genes needed in similar circumstances
-A promoter
-Regulatory sequences by the promoter (operator)
Regulatory regions are bound by regulatory proteins
What are operons in bacteria?
A cluster of genes under the control of a single regulatory signal or promoter. How bacterial genes are structured
What is negative control?
Gene repression where the regulatory protein binds to the operator sequence and inhibits expression
What is positive control?
Gene activation where the regulatory protein binds to the activator sequence and enhances expression
What does the lac operon do?
Codes for proteins involved in the catabolic processing of lactose
What are the three main genes in the lac operon?
LacZ, LacY and LacA
What is the function of LacZ?
Codes for Beta-galactosidase which breaks lactose into galactose and glucose
What is the function of LacY?
Codes for Lactose permease which transports lactose into the cell
What is the function of LacA?
Codes for Thiogalactoside transacetylase which has a role in detox
When is the lac operon expressed?
- High lactose concentration
- Low glucose concentration
What repressor controls negative control of the lac operon?
LacI
How does LacI block gene expression?
Binds to both of its binding sites, forming a DNA loop
What binds to the lac repressor to block gene inhibition?
Allolactose
What is incomplete repression?
When there is always a tiny level of expression
Why is incomplete repression needed for the lac operon?
Beta-galactosidase is needed for the repression of its own expression
What is diauxic growth?
When a population undergoes two separate phases of growth
How does cAMP levels show glucose concentrations?
Glucose entering the cell stops the activity of adenylate cyclase so that ATP is not converted into cAMP
What is the role of CRP in the lac operon?
Activates transcription
What is the method for CRPs activation of lac operon transcription?
Low glucose -> High cAMP -> cAMP binds CRP and changes its conformation -> CRP-cAMP binds creating a gentle bend in the DNA -> Transcription occurs
What is the function of the ara operon?
Encodes genes involved in the metabolism of arabinose, a 5-carbon carbohydrate
What are the three main enzyme-coding genes coded for by the ara operon?
araB, araA and araD
What are the functions of araA, araB and araD in the ara operon?
Catalyse the reaction turning Intracellular L-arabinose into Xylulose 5-phosphate
When is the ara operon expressed?
When there is a high arabinose concentration and a low glucose concentration
What is the role of CRP in the positive regulation of the ara operon?
When there is low glucose concentrations, CRP binds to the regulatory sequences, activating operon expression
What is the role of araC in the ara operon?
Acts as repressor and activator
How does the araC dimer bind when there is no arabinose?
Binds to I1 and O2, forming a loop in the DNA and blocking transcription
How does the araC dimer bind when there is arabinose present?
It binds to I1 and I2, forming a gentle bend in the DNA and causing efficient transcription
What are the genes in the bacteriophage lambda genome?
The viral components and the control of lysis and lysogeny
What are the three lytic cycle regulatory proteins in the bacteriophage lambda genome?
Cro, N and Q
What is the function of the cro lytic cycle regulatory protein in the bacteriophage lambda genome?
Binds to DNA to control transcription
What is the function of the N lytic cycle regulatory protein in the bacteriophage lambda genome?
Antitermination factor: allows transcription to proceed
What is the function of the Q lytic cycle regulatory protein in the bacteriophage lambda genome?
Antitermination factor: allows transcription to proceed
What are the three lysogenic cycle regulatory proteins in the bacteriophage lambda genome?
CI, CII and CIII
What is the function of the CI lysogenic cycle regulatory protein in the bacteriophage lambda genome?
Binds to DNA to control transcription
What is the function of the CII lysogenic cycle regulatory protein in the bacteriophage lambda genome?
Regulates CI function
What is the function of the CIII lysogenic cycle regulatory protein in the bacteriophage lambda genome?
Regulates CI function
What does the promotor PL code for in the bacteriophage lambda genome and what is the function of these genes?
N - Lysis
What does the promotor PR code for in the bacteriophage lambda genome and what is the function of these genes?
Cro and Q - Lysis control
O and P - Lytic replication
What does the promotor PR’ code for in the bacteriophage lambda genome and what is the function of these genes?
Phage particle components - Lysis
What does the promotor PRM code for in the bacteriophage lambda genome and what is the function of these genes?
CI - Repression of lytic promoters
What are the operator regions and their locations in the bacteriophage lambda genome?
OL at PL
OR and PR
What operator region does Cro bind with the highest affinity to?
Region 3
What are the results of Cro binding to operator region 3?
Blocks transcription from PRM but not from PR or PL so Cro and N are expressed
If the N protein in the bacteriophage lambda genome is expressed, what genes are expressed?
Cro and N
If the Q protein in the bacteriophage lambda genome is expressed, what genes are expressed?
Q and the genes for the phage infectious particle components
How is the lytic cycle controlled in the bacteriophage lambda genome?
- Cro binds to OL and OR, allowing expression of PL and PR
- N allows these transcripts to be extended
- O and P carry out replication of the viral DNA
- Q extends transcription from PR’ -> expression of other proteins that make up the infectious viral particle
What operator regions does CI bind with the highest affinity to?
1 and 2
What are the results of CI binding to operator regions 1 and 2?
Blocks transcription from PR and PL but not from PRM so only CI is expressed
How does a bacteriophage go from lysogeny to lysis?
Lysogenic prophage due to either spontaneous activation or DNA damage
What is the method of lysogenic prophage?
Starvation or DNA damage -> Activation of a protease -> Cleavage of CI -> Dissociation of CI from OL and OR -> Transcription from PL and PR -> Expression of lytic genes
Why would the lytic cycle be entered upon entry of a bacteriophage into a cell?
If there is:
- Low multiplicity of an infection - Rich media - Severe DNA damage
What is the multiplicity of infection?
The ratio of the number of virus particles to the number of target cells present in a defined space
Why would rich media mean the lytic cycle is entered?
High levels of N antitermination factor
What are the two possible methods and reasons for expression of CI?
- From PRM: Repression maintenance. Activated by CI
- From PRE: Repression establishment. Activated by CII
What are the promoters activated by CII and why are each of them activated?
- PI: Enzymes to integrate phage genome into the bacterial genome
- PRE: CI repressor
- PaQ: Prevents Q expression and so that of the lytic phase
What is the method of repression establishment in the bacteriophage lambda genome?
- CII made from PR during delayed early phase of infection
- CII protein climbs above the threshold value
- CII induces synthesis of CI from PRE
- CI binds to OR and OL and blocks transcription of lytic genes from PR and PL
How is CI level controlled by CII/CIII/FtsH
- CI represses lytic promoters -> lysogeny
- CII induces expression of CI from PRE
- High CII -> High CI -> lysogeny
- FtsH degrades CII
- CIII blocks FtsH protease activity
Why is CII only expressed during lysogeny establishment?
Its expression is repressed by binding of CI to OR
