16 How Genes Work

Question 0

What two scientist proposed: the one gene, one enzyme hypothesis?

Answer 0

George beadle and Edward tatum

Question 1

What is gene expression?

Answer 1

-the process of translating the information in DNA into functioning molecules within the cell

Question 2

What are nonfunctioning alleles called?

Answer 2

Knock-out, null, or loss of function alleles

Question 3

How did two scientist test one gene, one enzyme hypothesis?

Answer 3

• damage a gene by creating a mutant,
• then observe the resulting effect on the mutants phenotype

Results: inspired hypothesis and proposed that each gene contains information needed to make an enzyme

Question 4

What two scientist further tested the one gene, one enzyme hypothesis through the cells production of arginine?

Answer 4

Srb and Horowitz

Question 5

What did Srb and Horowitz hypothesized?

Answer 5

Different genes lead to the synthesis of each of the three enzymes required to make arginine

Question 6

How did Srb and Horowitz test their hypothesis?

Answer 6

• used radiation to create thousands of mutant cells
• performed genetic screening
• allowing them to select those mutants incapable of producing arginine

Question 7

What were the results of Srb and Horowitz experiment?

Answer 7

Results support the one-gene, one-enzyme hypothesis

• three distinct mutants were produced
• each was deficient in one of the three enzymes in the arginine metabolic pathway

Scientist then understood genes code instruction for making proteins

Question 8

What is the central dogma of molecular biology?

Answer 8

Francis crick proposed:

1) DNA is an information storage molecule
2) the sequence of bases in DNA is a kind of code
3) different combinations of bases specify the 20amino acids

• a particular stretch of DNA (gene) contains the information to specify the amino acid sequence of one protein.
• the information encoded in the base sequence of DNA is not directly translated into amino acid sequence of protein.

Question 9

What two scientist proposed RNA molecules act as a link between genes found in the nucleus and protein-manufacturing centers in cytoplasm?

Answer 9

François Jacob and Jacques Monod

Question 10

What is transcription?

Answer 10

The process by which the hereditary information in DNA is copied to RNA

Question 11

What is translation?

Answer 11

The process where the order of nucleotide bases is converted to the order of amino acids.

Question 12

Central dogma

Answer 12

• organism’s genotype: determined by sequence of bases in DNA
• organism’s phenotype: determined by the product of the proteins it produces
• alleles of the same gene differ in their DNA sequence
• proteins produced by different alleles of the same gene frequently differ in amino acid sequence

DNA —> mRNA —> protein

Question 13

Exceptions to central dogma

Answer 13

• many genes code for RNA molecules that do not function as mRNA and are not translated into protein. (perform other important functions in the cell)
• sometimes information flows backwards
• viral genes maybe composed of RNA and use reverse transcriptase, a viral polymerase, to synthesize as DNA version

Question 14

Who predicted each word in the genetic code contains three bases?

Answer 14

George Gamow

Question 15

What is a codon?

Answer 15

• The group of three bases

- specifies a particular amino acid

Question 16

What two scientist proved the three base codon?

Answer 16

Marshall Nirenberg and Philip Leder

Question 17

What is the code of the start codon?

Answer 17

AUG

Question 18

What are the codes for the three stop codons?

Answer 18

UGA, UAA, UAG

Question 19

What is a mutation?

Answer 19

• Any permanent change in an organism’s DNA
• A modification in a cells information archive
• A change in its genotype
• Able to create new alleles

Question 20

What are the different types of mutations?

Answer 20

• point mutations: results from a single base change
• chromosome-level mutations: larger scale, often result from the addition or deletion of chromosomes from the individual’s karyotype

Question 21

When does point mutation occur?

Answer 21

• occur when the DNA polymerase inserts the wrong base into the newly synthesized strand of DNA
• result in change of the DNA base sequence
• if the DNA polymerase proof reading and mismatch repair system fails

Question 22

What are missense or replacement mutations?

Answer 22

Results in changes in the amino acid sequence of the encoded protein

Question 23

Silent mutations

Answer 23

Do not change the amino acids sequence of the gene product

Question 24

Nonsense

Answer 24

• Change in nucleotide sequence that results in an early stop codon
• leads to mRNA breakdown or a shortened polypeptide, usually deleterious

Question 25

Frameshift

Answer 25

Addition or deletion of nucleotide

Reading frame is shifted, altering the meaning of all subsequent codons; almost always deleterious

Question 26

What are the three categories of mutations?

Answer 26

1) beneficial (increase fitness)
2) neutral (silent)
3) deleterious (decrease fitness)

Most mutations are neutral or slightly deleterious

Question 27

Polyploidy

Answer 27

Is an increase in the number of each type of chromosome (chromosome-level mutation)

Question 28

Aneuploidy

Answer 28

Is the addition or deletion of a chromosome (chromosome-level mutation)

Question 29

How does chromosome-level mutations change chromosome composition?

Answer 29

• Inversion: occur when sections of a chromosome break and rotate before rejoining
• translocation: occurs when a broken section of one chromosome becomes attached to another.