W1D2 - Nucleic Acids, Proteins, Genetics Intro Flashcards
Which macromolecule is the major component of the body by mass?
Protein
How many major amino acids are there in eukaryotes?
20
Amino acids form polypeptides by linking ______-to-_______ via _______ bonds.
linking head-to-tail via peptide bonds
What type of reaction forms peptide bonds between two amino acids? What is lost in this reaction?
Condensation reaction. H2O is lost.
On which end of an amino acid do new amino acids bond during polypeptide synthesis? So, how are sequences written?
On the C-terminal end, so sequences are written from N to C.
What is the central dogma of molecular biology?
DNA –replication–> DNA –transcription–> RNA –translation–> polypeptide
What is a nucleoside?
A pentose-base unit without any phosphate groups attached.
On which carbon is there no hydroxyl group on a deoxyribose sugar?
On the 2’ carbon
On which carbon is the base attached to in DNA/RNA?
1’ carbon
What type of bond attaches bases to pentose sugars?
glycosidic bond
RNA substitues _______ for thymine.
uracil
On which end of DNA/RNA does biological polymerization occur? Therefore, how are sequences written?
Polymerization occurs at the 3’ end.
Sequences are written from 5’ to 3’
Can certain proteins read base sequences in a 2x stranded DNA helix without melting/denaturing the DNA?
Yeah.
Define processivity.
A polymerase’s ability to catalyze many polymerization cycles.
Name the three major steps in DNA/RNA polymerization.
- Initiation
- Elongation
- Termination
Explain why DNA replication is semiconservative.
After cell division, one daughter cell has an original DNA strand and the other has the newly synthesized strand.
DNA replication is ________ on the lagging strand, replicating in chunks called _________ ________.
discontinuous; replicating in chunks called Okazaki fragments
What is the enzyme called that stitches Okazaki fragments together?
DNA ligase
What is the name of the enzyme that preserves the ends of DNA strands?
telomerase
Name the three RNA polymerases and generally what they make.
RNAPI - makes most of the rRNA
RNAPII - makes all premRNA –> mRNA
RNAPIII - makes tRNA
________ sequences allow specific cells to control gene expression.
Regulatory sequences
What does the promoter sequence do?
Tells RNAPII where to start.
What do enhancer sequences do? How long are they?
Around 10-30bp, they bind transcription factors or activators that help upregulate RNAP at the promoter.
Describe the four major steps in transcription.
- General transcription factors (GTFs) bind at the promoter, melting the DNA to form a transcription bubble.
- Other transcription factors bind to enhancer sequences, which later activate RNAP.
- Activating transcription factors bind to proteins called coactivators that loop around and contact RNAP and the GTFs to initiate polymerization.
- The bubble moves along with the RNAP-TFs complex until a terminator sequence is reached.
Are transcription factors a way in which cells regulate gene expression?
For sho.
Where in the cell does DNA replication happen? What about transcription? Translation?
DNA replication and transcription happen in the nucleus.
Translation happens in the cytoplasm.
Through what structure does mRNA travel to get from the nucleus to the cytoplasm?
through nuclear pores
Where in the cell does post-transcriptional mRNA processing occur?
In the nucleus.
Describe the three post-transcriptional modifications of pre-mRNA.
- 5’ cap: a 7-methyl guanosine is added to the 5’ end to protect against degradation by exonucleases and to signal to protein synthesis machinery that the RNA is, in fact, a mRNA.
- poly-A-tail addition to the 3’ end by poly-A polymerase.
- Splicing: remove introns, ligate exons together.
True or false: RNA processing and transcription happen simultaneously because processing machinery is physically linked to RNAPII.
True - they’re called “coupled reactions”
What is the purpose of differential mRNA splicing?
This allows for one pre-mRNA to yield many different mature mRNA variants. Therefore, the roughly 20,000 protein-coding genes in the human genome can encode >20,000 mRNA templates, and thus, proteins.
What is the pattern of inheritance for Marfan syndrome? What is the specific gene mutation? Name six clinical manifestations of the disorder.
Autosomal Dominant
Mutated Fibrillin gene on chromosome 15.
Clinical manifestations:
- Long extremities, fingers, toes (arachnodactyly)
- Pectus excavatum
- Scoliosis
- High risk for aortic dilatation and dissection
- Near-sightedness (myopia)
- Lens dislocation (ectopia lentis)
What is the difference between penetrance and expressivity?
Penetrance is an all-or-none phenomenon. A disease with incomplete penetrance will either manifest as having the disease or not.
Expressivity is gradated; and certain manifestations may show up in some patients and not in others.
What type of inheritance pattern is usually involved when looking at a disorder that is found in isolated or consanguineous populations?
Autosomal recessive
What is the pattern of inheritance for cystic fibrosis? Name the specific mutation most commonly found in those with European ancestry.
Autosomal recessive.
Δf508 mutation is most common amongst those with European ancestry.
Most disorders that exhibit AR inheritance involve a “_____ of function” gene mutation whereas most disorders with AD inheritance involve a “_____ of function” gene mutation.
Autosomal recessive: loss-of-function
Autosomal dominant: gain-of-function
What is the Hardy Weinberg equation? What do the variables represent?
p^2 + 2pq + q^2 = 1
p^2 represents homozygous dominant individuals
2pq represents heterozygotes
q^2 represents homozygous recessive individuals
What is the pattern of inheritance for Duchenne Muscular Dystrophy? What is the specific gene mutation?
Sex-linked (X-linked) recessive.
Dystrophin gene is mutated
Name three clinical manifestations of Duchenne Muscular Dystrophy.
- Weak proximal limb girdles
- Stiff-legged, waddling gait in early childhood
- Enlarged calves (pseudo-hypertrophy)
What is one possible explanation for when certain tissues in a woman’s body exhibit manifestations of an X-linked disorder?
Lyonization aka X-chromosome inactivation.
What is a Barr body?
A condensed-looking X chromosome after Lyonization has occurred.
What is the name of the enzyme that denatures the DNA double-helix during replication while the replication fork moves along?
Helicase
What proportion of lethal x-linked recessive diseases arise from new mutations? Why? So then, what are the chances the mother is a carrier?
1/3 of cases are due to new mutations because 1/3 of males that get the disease die and since disease rates have been steady, it must be that new mutations account for 1/3 of cases.
The chances the mother is a carrier is 2/3.
