Final Material Flashcards
How many amino acids comprise a protein?
20 different amino acids encoded by 20 different letters
What are the letters of the 4 different nucleotides that comprise DNA?
A (Adenine), G (Guanine), T (Thymine) and C (Cytosine)
What are 2 ways amino acids link together to form a type of protein?
- alpha-helix
- beta strand (or beta sheet)
Nucleotides that come together in pairs which form the DNA double helix structure is called what?
A codon
What’s the central dogma about the flow of genetic information?
DNA -> RNA -> protein
What’s the central dogma on what are the 2 steps in which the flow of genetic information occurs?
- Transcription (DNA -> RNA)
- Translation (RNA -> Protein)
What’s the intermediate molecule between DNA and protein?
RNA
How can an alphabet of 4 letters give rise to millions of proteins?
We need something (RNA) that can transcribe and link the 4 letters of DNA to 20 letters of proteins
What’s mRNA?
A messenger RNA
What’s DNA?
A polymer of nucleotides (2 complementary strands)
What’s RNA?
A polymer of nucleotides (single strand)
What’s a protein?
Chain or polymer of amino acids
What’s the unit of information?
The codon
The DNA alphabet comprises how many “letters”?
4 “letters”
The protein alphabet comprises how many “letters”?
20 “letters”
How many possible amino acids can a singlet DNA code form?
4 possible amino acids
How many possible amino acids can a doublet DNA code form?
16 possible amino acids (4^2 -> 4 to the power of 2)
How many possible amino acids can a triplet DNA code form?
64 possible amino acids (4^3 -> 4 to the power of 3)
What’s the 3 letter mRNA codon table?
- A genetic code for protein synthesis
- The codon table links each amino acid (20) to mRNA codons
- There are 16 different blocks, which include 64 codons (some that indicate stop or the start of transcription)
- Each block specifies the 1st and 2nd letter
What’s an example of an amino acid that has 6 different codons?
Lucine
The DNA coding strand is always what direction?
Always 5’ to 3’ direction
The mRNA sequence is a perfect copy of what sequence?
The mRNA sequence is a perfect copy of the DNA sense sequence, except T is subtituted with U (uracil)
What will be used to build the mRNA?
The anti-sense template
Which letter from the DNA sense sequence is replaced by a U in the mRNA sequence?
The letter T is substituted with U (uracil)
Illustrate the difference between a sense DNA coding strand and an anti-sense DNA template strand
Sense: 5’ ATGCATGCG 3’
Anti-sense: 3’ TACGTACGC 5’
What is translated into a protein sequence?
The mRNA codons
What can you predict about a protein with the mRNA codons?
if protein is hydrophilic or hydrophobic
Can only one nucleotide triplet encode a specific amino acid?
- No, multiple codons can encode the same amino acids
- Since there are 64 triplet combinations and 20 amino acids
- The genetic code is degenerate
How can we conclude that mutations may not change anything about the protein at all?
Because multiple codons can encode the same amino acids
What’s the difference between determining a protein primary structure from a DNA sequence and determining a DNA sequence from a protein primary structure?
- If you know the DNA sequence, you can accurately determine the protein primary structure
- If you know the protein primary structure you cannot determine the DNA sequence
- Because we are always uncertain about the 3rd base in the codon
What will happen if you put a gene into any kind of living organism?
It’ll express that protein (the protein may not function)
Why do we say the genetic code is universal?
- Because if you put a gene into any kind of living organism, it’ll express that protein even though the protein may not function
- Ex: if you take the green fluorescent gene from the cells of a jellyfish and implant it in a bacteria, a yeast cell and a mouse, they will all express that green fluorescent protein one way or another
What’s the structure of a gene?
- All genes have a start codon, a stop codon, a promoter and a terminator
- Start with promoter
- Then the start codon and stop codon (end of the protein sequence but not the end of the mRNA sequence)
- Then the terminator
What’s the function of the promoter in the gene structure?
Functions as a docking site, a place for the gene to sit down
What structures of the gene structure control where RNA polymerase will start transcribing the DNA sequence into an mRNA transcript?
The promoter and start codon
What letter sequence box is absolutely conserved in every promoter?
TATAAT box
What are the functions of RNA polymerase, the AAAA tail and mRNA in the gene structure?
- RNA polymerase transcribes a AAAA tail that is NOT translated
- The AAAA tail protects the mRNA until it is translated
What do promoters bind?
Promoters bind RNA polymerase
What does the promoter interact with?
Transcription Factors
What are the functions of transcription factors?
- They can influence the transcription start site
- They recruit RNA polymerase
What are the functions of the steps involved in how the promoter interacts with transcription factors to make RNA polymerase?
These steps control gene expression and can produce alternative yet functional proteins that are highly specialized for a cell type or stage in development
The template strand serves as a template for what?
For building and mRNA
How can transcription factors give you mRNA?
With transcription factors binding to the TATAAT box, you will have mRNA
What is considered a translation machine?
The ribosome
How do the sequences associated with nucleic acids and proteins interact with ribosomes?
They are linked mechanistically through the ribosome
Describe the structure of the ribosome
- Structure comprised of large subunit and small subunit
- The 1st binding site is called the A-site (aminoacyl) and is only functional when small and large subunits bind together -> it’s what the mRNA codes on
- Another binding site is the E-site (exit) and it will deal with covalent bonds
- The last binding site is the P-Site (peptidyl)
What’s the function of tRNA?
- Found in a ribosome
- It binds to amino acids
- It transfers amino acids to a mRNA molecule bound to a ribosome
- It’s reading mRNA and reading the amino acid
What’s the function of the ribosome?
- Where mRNA is translated into amino acid sequences
- Where the sequences associated with nucleic acids and proteins are linked mechanistically
How can a tRNA be recharged?
By binding to an amino acid
Describe the ribosome in action
- mRNA binds to the small subunit and the anticodon of a charged tRNA (+Met) binds the first codon
- The large subunit allows another tRNA+aa to enter
- A peptide bond is formed, the discharged tRNA is released and a new charged tRNA enters
When can the large subunit bind to the mRNA, tRNA and small subunit?
When mRNA binds to the small subunit and the anticodon of a charged tRNA (+Met) binds the first codon
How can you make a lot of similar proteins, which is essential for when releasing a signal?
Because you can have multiple ribosomes working on the same RNA at the same time
What determines where the sequence starts being read out on the mRNA interacting with a ribosome?
The start codon
When does the ribosome release the polypeptide?
- Ribosome reaches a stop codon on mRNA which is in line with the release factor
- The release factor in the ribosome promotes hydrolisis of GTP, which creates the energy to release the polypeptide
What does the sequence of the gene determine?
The amino acid sequence of the protein and its shape and function
Bacteria have ribosomes but they don’t have what?
Endoplasmic riticulum
What’s a silent mutation in DNA and how does it affect the shape and function of a protein?
- Mutations that occur in the 3rd base of the codon which will be silent
- It has not effect on the protein sequence or function, only on the nucleic acids
- Redundancy among codons
What’s a missense mutation in DNA and how does it affect the shape and function of a protein?
- Results in an amino acid substitution (change from Pro to Thr)
- Protein function might change
What’s a nonsense mutation in DNA and how does it affect the shape and function of a protein?
- Substitutes a stop codon for an amino acid
- Protein truncated, loss of function
Changes in the chemical nature of what group are very disruptive?
- R-group
How is sickle cell anemia disease caused?
- By a single change in one amino acid in a hemoglobin (acidic to non-polar)
- It has devastating effects on the hemoglobin
What’s a frameshift mutation?
- Mutation that leads to a different protein, or truncated-loss of function or gain of function
- Such mutations are the cause of many diseases
- Ex: AGCGUACCCUAC (Ser-Val-Pro-Tyr) to AGCGCCCUACUU (Ser-Ala-Leu-Leu)
What form of frame-shift mutation is particularly disruptive?
Frame-shift mutations that truncate the protein
What’s gain-of-function?
- A receptor that activates cell division without a signal
- Makes the protein lose the ability to respond to external signals
What’s required for all life?
Cell division
What happens when cell division goes wrong?
Unicellular organisms die and multicellular organisms get diseases
The one cell embryo is what kind of cell?
A stem cell
What’s the name of the cell that’s needed to produce any other cell?
Stem cell
What’s the self-sustaining hierarchical differentiation of cells?
- Stem cells
- Progenitor cells
- Mature cells
What do stem cells produce?
- Red and white blood cells
- These cells are also in our skin
How many cells does a human have?
10^13 cells
What’s the number of chromosome replications occurring per generation in humans?
10^16 divisions in the lifetime (10^13 -10^14 cells)
“Somatic” cells have what kind of cell division?
Binary tree division
“Stem” or “germ” cells have what kind of cell division?
One stem cell divisions
True of False: The cell cycle is different for different living cells
- False: The cell cycle is universal across all living cells
- The order never changes, and each step must be completed before the next step starts
What happens to cell division as you age?
Errors in cell division increase as you age
In what phase of the cell cycle does the cell actually undergo cell division?
During the “M” or mitosis phase
What does the cell cycle do?
It describes a series of events that occur during cell division
What about the cell cycle varies between organisms?
- The time required to complete each step, and for the entire cycle
- Ex: embryonic division are quite rapid because they lack the g1 & g2 phase since the cells are trying to reduce their size
The length of the cell cycle for each cell type is what?
It’s stereotyped
How long does a human cell take to divide?
24 hours
Cell divisions always occur at what angle from the last cell?
90º angle
What’s controlled for cyclin genes?
- The timing of expression of cyclin genes
- As a result, the concentration of cyclin protein is also controlled
What kind of cells have cyclin dependent Kinase?
All eukaryotic cells
What’s controlling cyclins in the cell cycle?
Transcription factors
How do cyclins interact with the cell cycle?
- Cyclin expression cycle
- There’s a set of cyclins specific to each phase for the cell cycle
What controls transitions in all eukaryotic cells?
Cyclin-dependent kinase (Cdk)
What needs to happen for Cdk to be active?
It needs to bind itself to ATP and phosphorylate itself which can only be done when it’s bound to a cyclin (co-enzyme)
When’s the only time that the kinase is active?
When the cyclin is bound to it
Describe the Cdk cycle
- cyclin binds to Cdk1
- A phosphate-donating protein (kinase) binds to Cdk
- Cyclin/Cdk complex is phosphorylated
- ATP binds to Cdk
- Cyclin-Cdk is now active
- The cyclin specifies the targets
- ATP binds to the target protein
- Cdk phosphorylates the target and releases it and seperates from cyclin
- Back to step 1
What are the different phases of the cell cycle?
- G1 phase (interphase) -> cell growth
- S phase (interphase) -> DNA synthesis
- G2 phase (interphase) -> cell growth
- Mitosis phase (mitotic phase)
- Cytokinesis phase (mitotic phase)
In what phase of the cell cycle do we see the formation of 2 daughter cells?
Mitotic phase
What’s E2F and what is it needed for?
- Transcription factor
- Needed to express 100s of genes in G1 that are needed for all later phases of the cell cycle
- START of cell cycle
Describe the Rb regulation of the cell
- Unphosphorylated Rb binds transcription factor E2F
- E2F can’t bind the DNA, and transcription is blocked
- Cell growth then triggers the phosphorylation of Rb
- Phosphorylated Rb releases E2F, which binds the DNA and turns on gene expression, thus advancing the cell cycle