W1D2 - Nucleic Acids, Proteins, Genetics Intro

Question 1

Which macromolecule is the major component of the body by mass?

Answer 1

Protein

Question 2

How many major amino acids are there in eukaryotes?

Answer 2

20

Question 3

Amino acids form polypeptides by linking ______-to-_______ via _______ bonds.

Answer 3

linking head-to-tail via peptide bonds

Question 4

What type of reaction forms peptide bonds between two amino acids? What is lost in this reaction?

Answer 4

Condensation reaction. H2O is lost.

Question 5

On which end of an amino acid do new amino acids bond during polypeptide synthesis? So, how are sequences written?

Answer 5

On the C-terminal end, so sequences are written from N to C.

Question 6

What is the central dogma of molecular biology?

Answer 6

DNA –replication–> DNA –transcription–> RNA –translation–> polypeptide

Question 7

What is a nucleoside?

Answer 7

A pentose-base unit without any phosphate groups attached.

Question 8

On which carbon is there no hydroxyl group on a deoxyribose sugar?

Answer 8

On the 2’ carbon

Question 9

On which carbon is the base attached to in DNA/RNA?

Answer 9

1’ carbon

Question 10

What type of bond attaches bases to pentose sugars?

Answer 10

glycosidic bond

Question 11

RNA substitues _______ for thymine.

Answer 11

uracil

Question 12

On which end of DNA/RNA does biological polymerization occur? Therefore, how are sequences written?

Answer 12

Polymerization occurs at the 3’ end.

Sequences are written from 5’ to 3’

Question 13

Can certain proteins read base sequences in a 2x stranded DNA helix without melting/denaturing the DNA?

Answer 13

Yeah.

Question 14

Define processivity.

Answer 14

A polymerase’s ability to catalyze many polymerization cycles.

Question 15

Name the three major steps in DNA/RNA polymerization.

Answer 15

1. Initiation
2. Elongation
3. Termination

Question 16

Explain why DNA replication is semiconservative.

Answer 16

After cell division, one daughter cell has an original DNA strand and the other has the newly synthesized strand.

Question 17

DNA replication is ________ on the lagging strand, replicating in chunks called _________ ________.

Answer 17

discontinuous; replicating in chunks called Okazaki fragments

Question 18

What is the enzyme called that stitches Okazaki fragments together?

Answer 18

DNA ligase

Question 19

What is the name of the enzyme that preserves the ends of DNA strands?

Answer 19

telomerase

Question 20

Name the three RNA polymerases and generally what they make.

Answer 20

RNAPI - makes most of the rRNA

RNAPII - makes all premRNA –> mRNA

RNAPIII - makes tRNA

Question 21

________ sequences allow specific cells to control gene expression.

Answer 21

Regulatory sequences

Question 22

What does the promoter sequence do?

Answer 22

Tells RNAPII where to start.

Question 23

What do enhancer sequences do? How long are they?

Answer 23

Around 10-30bp, they bind transcription factors or activators that help upregulate RNAP at the promoter.

Question 24

Describe the four major steps in transcription.

Answer 24

1. General transcription factors (GTFs) bind at the promoter, melting the DNA to form a transcription bubble.
2. Other transcription factors bind to enhancer sequences, which later activate RNAP.
3. Activating transcription factors bind to proteins called coactivators that loop around and contact RNAP and the GTFs to initiate polymerization.
4. The bubble moves along with the RNAP-TFs complex until a terminator sequence is reached.

Question 25

Are transcription factors a way in which cells regulate gene expression?

Answer 25

For sho.

Question 26

Where in the cell does DNA replication happen? What about transcription? Translation?

Answer 26

DNA replication and transcription happen in the nucleus.

Translation happens in the cytoplasm.

Question 27

Through what structure does mRNA travel to get from the nucleus to the cytoplasm?

Answer 27

through nuclear pores

Question 28

Where in the cell does post-transcriptional mRNA processing occur?

Answer 28

In the nucleus.

Question 29

Describe the three post-transcriptional modifications of pre-mRNA.

Answer 29

1. 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.
2. poly-A-tail addition to the 3’ end by poly-A polymerase.
3. Splicing: remove introns, ligate exons together.

Question 30

True or false: RNA processing and transcription happen simultaneously because processing machinery is physically linked to RNAPII.

Answer 30

True - they’re called “coupled reactions”

Question 31

What is the purpose of differential mRNA splicing?

Answer 31

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.

Question 32

What is the pattern of inheritance for Marfan syndrome? What is the specific gene mutation? Name six clinical manifestations of the disorder.

Answer 32

Autosomal Dominant

Mutated Fibrillin gene on chromosome 15.

Clinical manifestations:

1. Long extremities, fingers, toes (arachnodactyly)
2. Pectus excavatum
3. Scoliosis
4. High risk for aortic dilatation and dissection
5. Near-sightedness (myopia)
6. Lens dislocation (ectopia lentis)

Question 33

What is the difference between penetrance and expressivity?

Answer 33

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.

Question 34

What type of inheritance pattern is usually involved when looking at a disorder that is found in isolated or consanguineous populations?

Answer 34

Autosomal recessive

Question 35

What is the pattern of inheritance for cystic fibrosis? Name the specific mutation most commonly found in those with European ancestry.

Answer 35

Autosomal recessive.

Δf508 mutation is most common amongst those with European ancestry.

Question 36

Most disorders that exhibit AR inheritance involve a “_____ of function” gene mutation whereas most disorders with AD inheritance involve a “_____ of function” gene mutation.

Answer 36

Autosomal recessive: loss-of-function

Autosomal dominant: gain-of-function

Question 37

What is the Hardy Weinberg equation? What do the variables represent?

Answer 37

p^2 + 2pq + q^2 = 1

p^2 represents homozygous dominant individuals

2pq represents heterozygotes

q^2 represents homozygous recessive individuals

Question 38

What is the pattern of inheritance for Duchenne Muscular Dystrophy? What is the specific gene mutation?

Answer 38

Sex-linked (X-linked) recessive.

Dystrophin gene is mutated

Question 39

Name three clinical manifestations of Duchenne Muscular Dystrophy.

Answer 39

1. Weak proximal limb girdles
2. Stiff-legged, waddling gait in early childhood
3. Enlarged calves (pseudo-hypertrophy)

Question 40

What is one possible explanation for when certain tissues in a woman’s body exhibit manifestations of an X-linked disorder?

Answer 40

Lyonization aka X-chromosome inactivation.

Question 41

What is a Barr body?

Answer 41

A condensed-looking X chromosome after Lyonization has occurred.

Question 42

What is the name of the enzyme that denatures the DNA double-helix during replication while the replication fork moves along?

Answer 42

Helicase

Question 43

What proportion of lethal x-linked recessive diseases arise from new mutations? Why? So then, what are the chances the mother is a carrier?

Answer 43

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.