Molecular Genetics Flashcards
What is centrifugation?
- Separating particles of different sizes and densities by spinning them at high speeds,
- Heavier particles migrate to the bottom of the tube,
- Meselson and Stahl used centrifugation to prove DNA replicated by SemiConservative method
What is a complementary strand?
A strand of DNA with bases that match another strand of DNA
What is conservative replication?
A theory of DNA replication
- The original strands of DNA stayed intact and two new strands form
- One of which forms a complete copy of the original DNA double helix,
- The other forms a completely different DNA double helix
- Proved wrong by M/S
What is dispersive replication?
A theory of DNA replication
- The original strands of DNA are broken down and remade with new nucleotides scattered inside to make two double helixes
- Proved wrong by M/S
What is an isotope?
Atoms of the same proton number with a different neutron number/mass
What is a parent strand of DNA?
The template for constructing the new the DNA double helix
What is semiconservative replication?
A theory of DNA replication
- The original DNA splits in two and acts as a template
- Another half of DNA is synthesized and added to the template half
- Two DNA strands are produced, made half of the original DNA and half of new DNA that was added following the original template
- Proven true by M/S
What is a bacteriophage?
A virus that infects bacteria
- Used to prove DNA is the genetic material, not proteins
What is a viral coat?
A protein layer around a virus,
- Can be labeled with radioactive sulfur to trace whether proteins enter an infected cell
What is radioactive labeling?
To trace a chemical compound, replace some of the atoms with a radioactive isotope,
- This radioisotope can be followed from reactants to products
Who were Meselson and Stahl?
They proved DNA replicates in a semiconservative fashion
Who were Hershey and Chase?
Concluded that the genetic material of the bacteriophage was DNA, not protein
Who were Watson and Crick?
Developed the double-helix model of DNA
Who was Rosalind Franklin?
She used X-ray diffraction to discover the double helix structure of DNA
What are histones?
Globular proteins that assist DNA in condensing into chromosomes
What are introns?
Non-coding segments of nucleic acid that lie between coding sequences
What is a 5’ cap?
Repeating guanine nucleotides at the end of mRNA transcripts
What is an anticodon?
A three-nucleotide sequence in tRNA that compliments an mRNA
What is central dogma?
Genes specify the sequence of mRNA, which specify the sequence of proteins
What is a codon?
3 consecutive nucleotides in mRNA determines which tRNA will attach to the mRNA and deposit a specific amino acid into the protein chain
What is an exon?
Sequence present in protein mRNA after completion of pre-mRNA splicing
What is the initiation site in protein synthesis?
Nucleotide from which mRNA synthesis proceeds in the 5’-3’ direction, denoted with a+1
What is an intron?
A section in DNA that is not coded between coded sequences
What is a non-template strand?
A complementary strand to the parent DNA strand,
- exactly the same as an mRNA strand except for the Uracil in mRNA is a Thymine in DNA strands
What is a nonsense codon?
One of the three mRNA codons that stop protein synthesis
- A codon that doesn’t code any amino acid
What is a poly-A tail?
A modification was made to the 3’ of pre-mRNA to protect it from degradation and when it is exported from the nucleus
What is splicing?
The process of removing introns and reconnecting exons in a pre-mRNA
- removing the non-coded areas of DNA in mRNA and reconnecting coded areas
What is a TATA box?
A conserved promotor sequence in eukaryotes and prokaryotes that help to establish the initial site for transcription
- The site where transcription begins
What is a template strand in protein synthesis?
A strand from parent DNA that creates the complementary mRNA
What is a transcription bubble?
Region of locally unwound DNA that allows for the transcription of mRNA
What is gene expression?
conversion of encoded DNA to mRNA then a protein
- The process of protein synthesis
What are large 60S ribosomal subunits?
A second, larger ribosomal subunit that binds to the RNA to translate it into protein
What are small 40S ribosomal subunits?
Ribosomal subunits that bind to the RNA to translate into a protein
What are the two stages of protein synthesis?
- Transcription
- Translation
Describe transcription?
- DNA unwinds
- RNA Polymerase places RNA starting at the TATA box and synthesizes a complimentary mRNA primary transcript to the open DNA,
- The mRNA then goes through RNA splicing, conducted by the spliceosome and all the introns are removed and exons are bound back together
- Then a 5’ Cap and poly-A tail are placed at the end of the mRNA strand to create a finished, mature mRNA
- The mRNA leaves the nucleus while being checked at the nuclear pores
Describe translation?
- mRNA enters a ribosome
- mRNA is paired with tRNAs that bring an amino acid for every 3 nucleotides
- Once on tRNA has matched with a codon of the mRNA, the mRNA shifts so that another tRNA can add an amino acid
- This creates an amino acid chain as the amino acids from the tRNA bind together
- The protein stops synthesizing once the mRNA is read to have a stop codon, a codon that does not code for an amino acid
What is the purpose of protein synthesis?
To use the genetic code in our DNA to produce proteins that we are coded to display in our genome
What is DNA polymerase?
An enzyme that places DNA and connects individual nucleotides to each other to make a DNA molecule
What is a deletion in protein synthesis?
A change in chromosomes in which a fragment of the chromosomes is removed before transcription,
What is a frameshift in protein synthesis?
A mutation that causes the reading of the mRNA codons to shift,
- An additional base is added into the DNA code, creating a shift in the codons which are made in groups of 3
What is an insertion in protein synthesis?
A mutation that adds one or more nucleotide pairs to a gene
What is mismatch repair in protein synthesis?
When specific enzymes remove and replace incorrect pairs of nucleotides
What is a missense mutation in protein synthesis?
A mutation that changes only one amino acid
What is a mutation?
A random error in gene replication that leads to a change
What is a nonsense mutation?
A mutation that changes an mRNA codon to one of the three stop codons,
- Protein is shorter and usually nonfunctional
What is a nucleotide excision repair?
Replacing damaged segments of DNA by using an undamaged strand as a guide
What is a point mutation?
A genetic mutation where a single DNA base pair has been changed
What is proofreading in protein synthesis?
Looking for errors in DNA
What is a silent mutation?
A mutation that has no effect on the amino acid on a codon because the change in base codes for the same amino acid
What is telomerase?
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells
What is a telomere?
Repetitive DNA at the end of a eukaryotic chromosome.
What are the two types of mutations?
- Point
- Frame-shift
What mutations have an effect on the protein produced in protein synthesis?
- Missense
- Non-sense
What is a conservative mutation?
When the amino acid that changes is similar to the original one,
- Has little effect on the protein as a whole
What is non-conservative mutation?
When the amino acid that changes is completely different from the original one,
- This will change the protein
- e.g. sickle cell disease.
What is an operon?
A group of genes that are transcribed together as a unit
What is a repressor and what is its function in the regulation of tryptophan production?
A repressor is a protein that binds to the operating site on a strand of DNA, it prevents the movement of mRNA across the DNA and therefore prevents transcription
How does a repressor bind to the operator and when does it happen on the typ operon?
Repressors bind to operators when the levels of tryptophan are high in order to prevent the body from producing too much
- Tryptophan binds to the repressor when it is abundant and changes the shape of the repressor so that it can fit onto the DNA strand and block any mRNA that tries to undergo transcription,
- When there is a lack of tryptophan in the body the repressor remains in its original shape and cannot bind to the DNA strand because it does not fit properly
When is tryptophan synthesized?
When levels get too low,
- Repressors doesn’t prevent transcription when the levels of tryptophan are low so more can be produced
What are the two sites that work together to allow the enzyme that breaks down lactose to be made?
- CAP binding site
- Operator site
What conditions must be true for the lac operon to be used?
- Low levels of glucose
- High levels of lactose
What does the lac operon code for?
An enzyme that breaks down lactose
- lactase
How does the lac operon produce an enzyme?
- A molecule called cAMP is abundant in the absence of glucose and binds to a CAP molecule
- The CAP enzyme is then activated and binds to the CAP site on the DNA strand, bending the site,
- This gives room for RNA polymerase to bind to the operator site and undergo transcription of the lac operon (made of 3 genes)
How is the lac operon inhibited from creating an enzyme?
- If there is a high amount of glucose and a low amount of lactose, the CAP enzyme does not bind to a cAMP molecule,
- This means the CAP site will not bend and make room for the RNA polymerase
- Also, a lack repressor binds to the operator to prevent transcription while lactose is absent,
- When lactose is present, it binds to the lac repressor and inactivates it, preventing it from attaching to the operator site and allowing the lactose digesting enzyme to be made
Why is it important that levels of lactose determine how much of the lactose digesting enzyme is made?
It ensures that the enzyme is only made when there is too much lactose, this makes production efficient as it only happens when necessary
How can gene expression be controlled?
Regulate the rate of transcription
- Regulatory proteins can bind to DNA to prevent RNA polymerase from binding
- Alternative splicing
- Access to transport channels
- Availability of amino acids and ribosomes
- Post-translation modification
What is alternative splicing?
Ordering the exons of an mRNA differently so that it codes for a different protein
What is constitutive transcription?
Genes that are expressed all the time
- Proteins that are made all the time, necessary proteins our body always needs like for glycolysis
What is regulated transcription?
Genes that are only expressed at certain times and in certain cells
- Proteins are made sometimes
What are transcription factors?
Proteins that are made in the cytoplasm but eventually translate into the nucleus to activate translation
- Only interact with specific genes
- Eukaryotes have 1000+
Can transcription factors interact with any gene?
No, only the genes whose transcription they can control
Explain how transcription factors are used to regulate transcription.
- A signal is received from the cell requesting proteins, most likely from a protein and the message being phosphorylation of another protein
- This phosphorylated protein interacts with another protein which is then phosphorylated by ATP and a series of interactions occur between proteins similarly
- The final protein in this series of phosphorylation then enters the nucleus through a nuclear pore and interacts with a transcription factor
- This transcription factor is phosphorylated and changes shape
- Then the transcription factor binds to a section of the DNA called the enhancer region which is further down from the transcription site
- The transcription factor then moves while still attached to the enhancer region and also binds to the starting site of transcription, folding the DNA
- This makes sure only a specific section of DNA is transcribed
