Unit 13

Question 1

What two studies of Archibald Garrod were evidence that genes encoded enzymes and inspired Beadle and Tatum?

Answer 1

1. Alkaptonuria
2. Phenylketonuria

Question 2

Mutations in what cause phenylketonuria?

Answer 2

Phenylalanine hydroxylase

Question 3

Mutations in what cause alkaptonuria?

Answer 3

Homogentisic acid oxidase

Question 4

What does alkaptonuria cause?

Answer 4

It causes a mutation in homogentisic acid oxidase and prevents the metabolizing of homogentisic acid

Question 5

What are three things that happens when we can’t metabolize homogentisic acid?

Answer 5

1. It accumulates in cells and tissues and is secreted in the urine
2. the acid accumulates in joints leading to benign arthritis
3. Oxidation products are black and detected in the diapers of newborns and also accumulate in cartilaginous areas, causing the ears and nose to darken

Question 6

What does phenylketonuria cause?

Answer 6

It causes a defect in phenylalanine hydroxylase which makes it so Phe can’t be converted to Tyr

Question 7

What are some symptoms of phenylketonuria?

Answer 7

Intellectual disability

Seizures

Should eat a diet low in protein and avoid diet coke

Question 8

What did Beadle and Tatum study that supported the One-Gene One-Enzyme hypothesis?

Answer 8

Studies of Neurospora (bread mold)

Question 9

What experiment did Beadle and Tatum first conduct on Neurospora?

Answer 9

1. They first induced a nutritional mutation into the experimental group and placed them into 5 tubes containing different mediums and observed which medium allowed the mutated neurospora to grow.
2. The neurospora only grew on the minimal medium with AA

Question 10

What was the second experiment Tatum and Beadle performed after learning the neurospora only grew on the medium containing AA?

Answer 10

1. They made individual 20 test tubes that all had minimal medium but they each had a different AA in it.
2. The neurospora only grew on the complete medium and the medium containing tyrosine.

Question 11

Why not one-gene one-protein or one-gene one-polypeptide chain

Answer 11

1. Nearly all enzymes are proteins but not all proteins are enzymes
2. Some proteins have a subunit structure with two or more polypeptide chains
3. Sickle cell anemia (defect in the beta globulin subunit of hemoglobin)

Question 12

Explain sickle-cell anemia:

Answer 12

It is a recessive genetic disease where erythrocytes become elongates under low oxygen tension.

Afflicted individuals are homozygous for Hbs hemoglobin allele

Question 13

What is a homopolymers?

Answer 13

A polymer of a single type of nucleotide

Question 14

How did we discover UUU encodes for Phe?

Answer 14

1. A homopolymer of U’s, poly(U) mRNA as added to a test tube containing a cell-free translation system, 1 radioactively labeled amino acids, and 19 unlabeled amino acids
2. The tube was then incubated at 37 degrees Celsius so translation could take place and then the protein was filters and checked for radioactivity
3. This was then repeated with 20 tubes all containing a different amino acid until the tube labeled Phe was shown have radioactive Phe.

Question 15

How did we discover UUU encodes for Phe?

Answer 15

1. A homopolymer of U’s, poly(U) mRNA as added to a test tube containing a cell-free translation system, 1 radioactively labeled amino acids, and 19 unlabeled amino acids
2. The tube was then incubated at 37 degrees Celsius so translation could take place and then the protein was filters and checked for radioactivity
3. This was then repeated with 20 tubes all containing a different amino acid until the tube labeled Phe was shown have radioactive Phe.

Question 16

What is a charged tRNA?

Answer 16

a tRNA that has an AA attached to it.

Question 17

How many aminoacyl synthase are there?

Answer 17

20 - one for each AA

Question 18

What are Isoaccepting tRNAs?

Answer 18

they carry the same AA but have different anticodons

Question 19

What enzyme can be used to generate a synthetic messenger RNA without the need for a DNA template?

Answer 19

Polynucleotide phosphorylase

Question 20

What amino acid is encoded for by the codon 5’-UCC-3’?

Answer 20

Serine

Question 21

How was it determined that UUU encodes phenylalanine?

Answer 21

Marshall Nirenburg and Johann Heinrich Matthaei created synthetic RNAs using the enzyme polynucleotide phosphorylase which randomly links together any available nucleotides. They added this to a solution of uracil nucleotides and created a homopolymer of only Uracil. They added this to twenty test tubes each with the components necessary for translation, all 20 amino acids, and a different radioactively labeled amino acid in each of the test tubes. Only the test tube labeled phenylalanine contained a radioactive protein.

Question 22

What is meant by the genetic code being degenerate?

Answer 22

1. Refers to the fact that the genetic code contains more codons than are needed to specify all 20 common amino acids.
2. Amino acids may be specified by more than one codon

3.Francis Crick borrowed the term from quantum physics, where it describes multiple physical states that have equivalent meaning

Question 23

Where does translation begin?

Answer 23

Starts at AUG but only AUG with the Shine-Dalgarno sequence ( preceding it.

Question 24

What two subunit comprise a ribosome?

Answer 24

1. Large subunit (50s)
2. Small subunit (30s)

Question 25

Describe the process of Initiation in translation:

Answer 25

First, If-3 binds to the small subunit preventing the large subunit from binding, thus allowing the small subunit to attach to mRNA.

Next, a tRNA charged with N-formyl methionine (fMet) forms a complex with IF-2 and GTP which then binds to the initiation codon while IF-1 joins the small subunit.

Finally, All initiation factors dissociate from the complex, GTP is hydrolyzed to GDP and the large subunit joins to create a 70s initiation complex

Question 26

What is the primary protein structure?

Answer 26

A linear chain of AA

Question 27

What is the secondary protein structure?

Answer 27

Protein folds in a repeating pattern based on hydrogen bonds between nearby AAs

Ex: silk moth fibrin

Question 28

What are chaperones?

Answer 28

They are proteins that assist in the folding of post translated proteins

Question 29

What is the tertiary structure:

Answer 29

Further folding into an irregular patter based on the following four properties

1. Bonds
2. Electrostatic forces
3. Vander Waals forces
4. Interactions between R groups

Ex: Myoglobin

Question 30

What is the quaternary structure of proteins?

Answer 30

Two or more polypeptide chains in association with one another.

Question 31

What is the peptidyl transferase enzyme and what is its function?

Answer 31

Is a protein-RNA complex (ribozyme) that is present in the large subunit of the ribosome.

Its function is to move the growing polypeptide chain from the tRNA in the P site to the tRNA in the A site

Question 32

Explain elongation during translation:

Answer 32

1. A peptide bond forms between the amino acids in the P and A sites, and the tRNA in the P site releases its amino acid
2. The ribosome moves down the mRNA to the next codon (translocation), which requires EF-G and GTP
3. The tRNA that was in the P site is now in the E site, from which it moves into the cytoplasm
4. The tRNA that occupied the A site is now open and ready to receive another tRNA.

Question 33

What happens during the termination phase of translation?

Answer 33

1. When the ribosome translocates to a stop codon, there is no tRNA with an anticodon that can pair with the codon in the A site
2. RF-1 attaches to the A site and RF-3 forms a complex with GTP and binds to the ribosome
3. The polypeptide is release from the tRNA in the P site
4. The GTP associated with RF-3 is hydrolyzed to GDP and the tRNA, mRNA, and release factors are released from the ribosome.