Molecular Genetics Flashcards
What was Griffiths experiment?
(1928) Found that genetic material or (transforming principle) is passed from the nonvirulent strain to the heat killed virulent strain.
Inject mice with various strains of a virus and found that the mixture between two non lethal virus’s killed the mouse, resulting in his conclusion/
What was the Avery-Macleod-McCarthy experiment?
1944 - Tried to find the transforming principle from Griffith’s experiment
Did this by testing proteins (though to be the transforming principle at the time), RNA, DNA
They found that DNA was the material that carried hereditary information
How did the Avery-McCarthy- Macleod experiment work?
They introduced enzymes to break down proteins, DNA, RNA, and observed that the mixture of the 2 non lethal viruses was only affected when DNA was broken down meaning DNA must be the transforming principle
What was the Hershey and Chase experiment?
After the Avery-Macleod-McCarthy experiment some still believed proteins was the transforming principle
By using radioactive isotopes, the should that bacteriaphages pass their DNA into a bacteria to infect it and not their protein
What role did Franklin, Watson, and Crick have in the discovery of DNA?
Using X-Ray crystallography (X-Ray pic from Franklin), Watson and Crick were able to determine the shape of DNA.
Franklin published a much more strong mathematical explanation however was not given full credit due to sexism
Who was Thomas Hunt Morgan?
The fruit fly guy - He is famous for studying fruit flys and discovered genetic linkage and x-linked traits
What is DNA?
Deoxyribonucleic Acid
A molecule composed of two chains that could around each other to form a double helix.
What does DNA carry?
Genetic instructions for the deveolpment, functioning, growth and reproduction of all known organisms.
What are the functions of Nucleic acids?
Used to carry genetic information in organisms
Carry messages that code for different genes with produce proteins
What are the two main types of nucleic acids?
Deoxyribonucleic acid
Ribonucleic acid (RNA, mRNA, tRNA)
What type of molecule is DNA?
A polymer, monomers are called nucleotides
What are the 5 types of nucleotides?
A - Adenine (Purine)
T - Thymine (Pyrimidine)
G - Guanine (Purine)
C - Cytosine (Pyrimidine)
U - Uracile (Replaces thymine in RNA)
What does each nucleotide consist of?
Sugar phosphate backbone and one nitrogen base
What is the location for bonding between sugar and phosphate?
The 3’ and 5’ position
What is each side of a right handed helix composed of?
Sugar-phosphate backbone
What are the ‘rungs’ of DNA?
Nitrogen bases
What are the nitrogen based connected by?
Hydrogen bonds
What is the relatinoship between Purines and pyrimidine?
Purine bonds w/ pyrimidine
A and T
G and C
Who was Erwin Chargaff?
He looked at DNA between different species and discovered various ‘rules’ regarding DNA
What are the Chargaffs rules?
- AT:GC is same for same species and different for different species
- A = T, G=c
- A+T doesn’t equal G + C
What is mtDNA?
DNA located in the mitochondria
Mom passes done mtDNA, beacuse the egg supplies mitochondria
How does DNA Condense into chromosomes
Histones (proteins) help wrap DNA - similar to garden hose
Furthermore, nucleosomes wrap around DNA into tighter and tigher coilds
When does DNA replication take place?
During S phase
What is step one of DNA replication?
DNA is unwound by helicase
What is helicase?
A specilized enzyme used to break the hydrogen bonds between nitrogen bases
What is the second step of DNA replication?
DNA polymerase pairs nucleotides to single strands of DNA in the 5’ to 3’ direction
The sugar-phosphate backbone is reformed
What is the outcome/problom with polymerase?
One strand becomes the leading strand and the other ‘laggs’ behind forming the lagging strand.
What happens to the lagging strand?
The DNA is copied backwards resulting in Okazaki fragments
What is semi-conservative replication?
Meaning each new strand has half old DNA and halkf new DNA
The first step of DNA replication can also be called Initiation. Please outline the Initation stage?
Helicase unzips DNA creating a replication fork (two make a bubble)
Step 2 can also be known as elongation. Please outline elongation.
Primase adds RNA Primer
Then…
DNA polymerase extends from this primer (copies ‘ to 3’) resulting in lagging strands
Step 3 can also be known as termination. Please outline termination?
Exonuclease removes primers
and DNA ligase joins fragments sealing DNA up
What is DNA proofreading?
DNA polymerase checks for these errors by checking the width of the helix.
What is the error rate of DNA replication?
Mistakes in the initial pairing of template nucleotides and complementry nucleotides occur at a rate of 1 per 100,000 base pairs
After DNA polymerase checks for errors it is 1/10 billion base pairs
What can result in replicaiton error?
Exposure to chemcials, virsuses and radiation cause damage to DNA, meaning the human body needs 130 enzymes to constantly check DNA for errors
What is a telomere?
Regions of repetitive nucleotide sequences at the end of a chromatid, protecting the chromosome from deterioration or from fusion with neighbouring chromosomes.
What is PCR?
Polymerase Chain Reaction
What are the steps involved in PCR?
- Denaturation of template DNA
- Annealing of primers to each original strand
- Exstension (elongation) of new DNA strands from primers
What is the purpose of SLR?
Amplify DNA
What does DNA encode for?
A protein which is a chain of amino acids. Each gene encodes for a chain of amino acids
What determines the sequence of amino acids?
The sequence of nucleotides
What does 3 nucleotides create?
A codon
What does a codon code for?
A specific amino acid
What is transcription?
The process of going from DNA to RNA
What must be done before a protein can be made?
The DNA must be read and converted into the messenger RNA (mRNA), through the process of transcription
What are the three steps of transcription?
Initiation
Elongation
Termination
What occurs during the Initiation stage?
RNA polymerase binds to a sequence of DNA called the promotor
What is the promotor?
Is a sequence of DNA found near the beginning of a gene.
What occurs in elongation?
One strand of DNA (Template strand), acts as a template for RNA polymerase. The polymerase builds and RNA molecule out of complementary nucleotides making a chain that grows from 5’ to 3’.
What is the difference between RNA and the coding (non-template) strand of DNA?
RNA has a Uracil rather then Thymine
What happens during the Termination stage?
Sequences called terminators signal that the RNA transcript is complete. Once they are transcribe they cause the transcript to be released from the RNA polymerase
What structure is mRNA?
A single helix
What is the difference between the nucleotides between RNA and DNA?
RNA has Uracil instead thymine
What is the difference between sugars in RNA from DNA?
RNA has ribose whereas DNA has deoxyribose
What are some of the additions that occur when mRNA transcript undergoes enzyme regulated modifications?
Addition of a poly-A tail
Addition of a GTP cap
Exicions of introns and retentions of exons
What is the puropse of the addition of a poly-A tail to pre-mRNA?
To protect the mRNA by keeping it stable
What are introns?
Sections of junk RNA which are removed during pre-mRNA processing
What is the group at the 5’ end called?
Cap
What is the group at the 3’ group called?
Tail
What is the cap made up of?
Modified guanine - protects transcript from being broken down
What is the tail composed of?
An enzyme adds 100-200 adenine nucloetides to end forming a poly end tail
What is RNA splicing?
Specific parts of the pre-mRNA called introns are removed by the spliceosome
What occurs after DNA has been transcribed into a single strand mRNA?
Read by ribosomes in the cell
How does the ribomosme “Read’ the mRNA sequence?
Read by codons (three nucleotides at a time) and attach corresponding amino acids by tRNA
What is the purpose of tRNA
Otherwise known as transfer RNA
Carry amino acids and an anti-codon that binds to the mRNA and attach their amino acid
How is the start of a polypeptide specifed?
Using a start codon - typically an AUG (methionine)
What signals the end of translation?
Stop codons, UAA, UAG, UGA
What is gene regulation?
The mechanism for turning a gene on and off
In bacteria where are related genes often found?
In bacteria, related genes are often found grouped together in operons.
A cluster under contorl of a single promoter is known as?
An operan (group of genes that do something similar)
What are molecules called if they can turn on an operan?
An inducer, the operan is said to be inducable
What is the molecule which turns an operan off called?
A corepressor, the operan is said to be repressible
When is the lac Operan expressed in bacteria?
When lactose is present and glucose is not
What are the two regulatory proteins needed fot the Lac Operan?
The lac repressor (lactose sensor)
Catabolite activator Protein (CAP) - acts as glucose sensor
When there is an absence of lactose what is the response by the Lac Operan?
The lac repressor binds tightly to the operator preveting transcription (bacteria doesnt break down lactose)
What occurs when lactose is present?
The lac repressor losses its ablity to bind to DNA. It floats off the operator allowing RNA polymerase to attach and transcribe the operan
What else is needed for transcription of the Lac operan?
Help from the catabolic activator protien - CAP helps RNA polymerase which doesnt bind well to the promotor
What is the process of different gene expression called in eukaryotes?
Differential gene expression - the expression of different genes by cells with the same genome
What is epigenetics?
The study of heritable changes in gene expression
What is the first type of Eukaryotic gene expression?
Regulation of Chromotin Structure
How does the regulation of chromotin structure work?
In histone acetylation, tails no longer bind to neighboring nucleosomes so chromatin has a looser structure. As a result transcription proteins have easier access to genes in an acetylated region
What is the second type of differential gene expression in Eukaryotes?
Transcription facotrs - protiens that regulate transcription of genes
How do transcripton factors work?
They bind to DNA at a certain point. Once its bound the transcription factor either makes it easier or hatrder for RNA polymerase to bind to the promoter of the gene
What is the relationship between activators and repressors in gene expression?
Both may be used in gene expression at the same time
After transcription where else can regulation occur?
- RNA Processing (Splicing, caping, poly-A tail addition)
- Messenger RNA translation and lifetime in the cytosol
- Protein modifications such as the addition of chemcal groups
What is alternative RNA splicing?
Different mRNA molecules are produced from the same primary transcript depending on which RNA segments or treated as Exons or Introns
What are regulators?
(mRNA translation/lifetime)
Molecules or mechanisms that control mRNA translation efficiency and stability, influencing protein production. They ensure proper gene expression post-transcriptionally.
What is miRNA?
MicroRNAis first transcribed as a long RNA molecule which forms base pairs with itself creating a hairpin
What is the purpose of miRNA hairpin?
Is cut making a fragment of RNA, which bind to a protein froming a RNA protein complex
What is the function of an RNA protein complex?
RNA-protein complexes assist in RNA processing (splicing), stability, transport, translation, and degradation.
How can proteins me modified?
Proteins can be editied (by removing an amino acid, add a chemical) to control activity
What is phosphrylation?
Adding a phosphate group to change protein behaviour
(In regard to Protein Modification)
What is Ubiquination?
A chemical marker that tags a protein for degredation
What are mutations?
Change in the nucleotide sequence (can be good, bad or neither)
What are spontaneous mutations?
Occur Naturally (result in genetic variation and evolution)
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What is Induced Mutations
Mutations casued by enviromental factors (Radition, chemicals)
What must happen for mutations to be passed down?
Must be passed down through sex cells
How can changes in DNA be used?
To examine how closely related species are
What are the three types of mutations?
There are three types of point mutations
- Missense Mutations
- Nonsense Mutations
- Insertion/deletion
What are missense mutations?
Change in nucleotide and results in a single amino acid change
Ex: CTC to CAC; Amino acid: Glu to Val
What are nonsense mutations?
Results in a STOP Codon
ATG to ATC; tyr to STOP
What are insertion/deletion mutations?
Nucleotide is removed or added
Results in a frame shifts
Very damaging as all amino acids are changed (usually ends in apoptosis)
What are chromosome mutations?
A change in ths tructure or number of chromosomes
What are the different types of chromosome mutations?
Duplications (Extra part)
Inversion (One peice reverses direction)
Deletions (Loses a part)
Translocation (One chromosome breaks off and attaches to other)
What is the endosymbotic theory?
Thta a Eukaryotic cell engulfed mitochondria and became upgraded
What is transduction?
Viruses that infect bacteria move peices of chromosomal DNA from one bacterim to another
What is conjugation?
DNA is transformed from bacterium to aonther using strucure called a pilus
What is transposition?
Chunks of DNA jump from one place to another within a genome, inserting copies of themselves in new spots
What is recombinant genetic modification?
Moving genetic material from one organism to another
What are the steps involved in genetic recombinate modification?
- Use restriction enzymes to cut DNA at certain points
- If same enzyme is used on other organisms, sticky ends attach
- Using a plasmid you can put recombinant DNA into bactieral cells
- DNA Ligase fuses DNA together
What are sticky ends?
Overhanging pieces of spliced DNA
What is DNA fingerprinting?
Is a lab technique used to prosecute people who have commited crimes and establish paternity
How does DNA fingerprinting work?
The use of restriction enzymes cut DNA at certain points - every suspect has a different sequence of DNA so these enzymes cut DNA into different sizes depending on the DNA sequence
How are parts of DNA seperated during DNA fingerprinting?
DNA samples are placed in gel with electrodes at each end
When electricity is applied to the gel, DNA fragments migrate towards opposite end. Smaller DNA fragments move fruther from the well than larger DNA fragments
