Chapter `16

Question 1

What question did Beadle and Tatum test with Arginine metabolic pathway?

Answer 1

If there was a 1:1 ratio of genes to proteins.

Question 2

What is a genetic screen?

• Who used this to test what?
  pt. 1

Answer 2

1- you take a large population of cells. ( Nauraspa cells)
2- randomly mutagenize the genes in those cells.
( via UV or X-ray), so each cell has a random group of mutations then.
3- Place on media and allow for growth (containing Arginine)
4- transfer cells to media that lacked arginine.
5- Screen through the population looking for phenotypes that are indicative of a problem in whatever process you are studying. (look for cells that only grew in the presence of arginine.)
5- then you take the ones you interested in and study them further, to see where the mutations are.
6- establish a relationship between mutants and enzymes.
7- take each mutant( grew only the presence of arginine) and grew it in either ornithine or in citrulline or in arginine and used that data to characterize what step in the pathway that mutant was defective in.
( ornithine, citrulline or in arginine* are all steps in the metabolic pathway to get to arginine.)

Question 3

What were the results of beadle and Tatum’s genetic screen?

Answer 3

• They found three different types of mutants each associated with a defect in enzyme one, two, or three. Which further suggest that…
• The one-gene, one-enzyme hypothesis is correct.

Question 4

precursor—>ornithine—>citrulline—>arginine
Given this metabolic pathway, and if the mutant cells produced as a result of a genetic screen only saw growth in citrulline and arginine the cells would lack which enzymes

Answer 4

enzyme two.

Question 5

t/f every gene encodes for only one protein?

Answer 5

false, Beadle and Tatum’s experiment pointed to this idea, but that is not totally true.
- most of the time genes will encode just for one protein, but sometimes genes can encode for more than one protein.

Question 6

What is the genetic code?

Answer 6

• How the sequence of nucleotides in a gene is ultimately converted to the sequence of amino acids in a protein.

Question 7

What is the function of ribosomes and where are they found?

Where is DNA found?

Answer 7

• protein synthesis, in the cytosol and rough ER

- Nucleus.

Question 8

Since DNA is in the nucleus and ribosomes that synthesis proteins are in the cytosol, how do you carry the genetic information from the nucleus out to the ribosomes?

Answer 8

mRNA

Question 9

What is mRNA?

Answer 9

• The genetic information in the DNA is used to make a different type of nucleotide called an mRNA, which is then exported to the cytoplasm, where they are read by ribosomes ultimately to make the proteins.

Question 10

What is the central dogma of biology?

Answer 10

1. ) Genes are composed of DNA and their role is long term storage.
2. ) transcription
3. ) mRNA is produced
4. ) carries genetic info to the ribosomes.
5. ) translation occurs.

Question 11

What is transcription?

What is translation?

Answer 11

• DNA to mRNA

- Ribosomes reading mRNA and make the corresponding proteins.

Question 12

What about the central dogma of biology is grossly simplified?

Answer 12

• lack of awareness for differing types of RNA’s:
  rRNA & tRNA are necessary for translation
  miRNA’s, siRNAs, piwiRNAs (regulate translation)
  incRNA’s regulate chromosome structure.
• Overall lack of RNA’s associated with translation and transcription.

Question 13

How are the bases in DNA read?

Answer 13

• the genetic code is read in groups of three base pairs.

- every 3 bases in an RNA is read by the cell to make one amino acid in the corresponding protein.

Question 14

How do we know what three bases equate to an amino acid?

Answer 14

• begin by making synthetic mRNA of a known sequence.
• put in a test tube with known sequences of amino acids, ribosomes, and tRNA’s ,ect.
• look at the produced peptide and see what the base code produced is.

Question 15

What is a codon?

Answer 15

• it is a sequence of 3 bases in an mRNA that contain the information needed to make a particular amino acid.

Question 16

Where do you start the reading frame of an mRNA?

Answer 16

• the first codon or start codon appears at the 3 bases AUG.

- the last codon in the reading frame or the stop codon is referred to as stop codon, and is either UAA or UAG. or UGA

Question 17

What is always the first amino acid in a protein?

Answer 17

• Methionine.

Question 18

t/f: the genetic code is redundant?

- what does this mean?

Answer 18

• T, it is redundant.

- most amino acids are specified by more than one codon.

Question 19

What is the most abundant amino acid seen in proteins?

Answer 19

• glutamic acid.

Question 20

t/f there a correlation to the abundance of an amino and how man codons encode for it?

Answer 20

false, those variables are independent of one anther.

Question 21

What is the template strand?

Answer 21

• the DNA strand that is used to make the mRNA via transcription.

Question 22

What is the non-template strand?

Answer 22

• the reverse complement of the DNA template strand, thus is the mRNA.
• Then you find

Question 23

How would you predict the amino acid sequence.

Answer 23

• Given the non-template strand , you would then find the start codon and use a genetic code table to figure out what the outcome should be.

Question 24

What are point mutations?

Answer 24

single base changes to a gene.

Question 25

When do single point mutations typically occur?

Answer 25

- during uncorrected errors of DNA replication

Question 26

What is the effect of a point mutation on a protein?

Answer 26

silent mutation: change in nucleotide sequence that does not change the amino acid specified by a codon. Or Missense: change in nucleotide sequence that changes the amino acid specified by codon. This results in a change to the primary structure of protein may be beneficial, neutral, or deleterious. Or Nonsense: change in nucleotide sequence that results in an early stop codon. Resulting in mRNA breakdown or shortened polypeptide; usually deleterious. Or Frame shift: addition or deletion: of a nucleotide; resulting in reading frame is shifted, altering the meaning of all subsequent codons; almost always deleterious. - most destructive ,