Gene Structure and Expression

Question 1

Garrod

Answer 1

studied alkaptonuria disease

• metabolic disorder caused by alteration in a gene that encodes the enzyme that metabolizes this chemical
• turns black in air
• inherited

Question 2

Beadle and Tatum

Answer 2

grow mould on minimal media

-Hypothesis: each mutant had defective gene for enzyme needed to synthesize a particular nutrient

Question 3

One gene-one enzyme hypothesis

Answer 3

direct relationship between genes and enzymes

-later altered

Question 4

One gene-one polypeptide hypothesis

Answer 4

• not all proteins are enzymes
• functional proteins sometimes contain one or more polypeptides
• different genes encode each polypeptide

Question 5

Transcription

Answer 5

• nucleotide sequence in DNA is copied into a complementary sequence in an RNA molecule
• template strand of DNA is used to create messenger RNA (mRNA)

Question 6

Translation

Answer 6

• sequence of nucleotides in mRNA molecule specifies amino acid sequence in polypeptide
• ribosome assembles the amino acid sequence

Question 7

Which way are DNA template strands read?

Answer 7

3’ to 5’

Question 8

Which way are mRNA strands read?

Answer 8

5’ to 3’

Question 9

Start codon

Answer 9

AUG, methionine, establishes reading frame

Question 10

Stop codon

Answer 10

UAA, UAG, UGA

end of a polypeptide-encoding mRNA sequence

Question 11

How is transcription different than DNA replication

Answer 11

• only one DNA strand used as a template
• only transcribes the genes
• RNA polymerases used’
• RNA are single strands
• Uracil replaces thymine

Question 12

RNA polymerases

Answer 12

no primers needed

-RNA is made 5’ to 3’

Question 13

Promoter

Answer 13

• control sequence initiates transcription
• upstream of transcriptional unit
• where RNA polymerase binds

Question 14

Transcriptional unit

Answer 14

-portion of gene that is copied into RNA

Question 15

Terminator

Answer 15

-signals the end of transcription of a gene

Question 16

TATA box

Answer 16

The TATA box in the promoter is about 30 base pairs upstream of the transcription will initiate

Question 17

5’ Cap

Answer 17

site where ribosome attaches to mRNA

Question 18

PolyA Tail

Answer 18

protects mRNA from RNA-digesting enzymes

Question 19

Introns

Answer 19

non-protein-coding sequences in the pre-mRNA

must be removed before translation

Question 20

Exons

Answer 20

amino acid coding sequences in pre-mRNA

joined together sequentially in final mRNA

Question 21

Spliceosome

Answer 21

pre-mRNA

small ribonucleoprotein particles (snRNP)

Question 22

snRNPs

Answer 22

• bind to introns
• loops introns out of the pre-mRNA
• clip the intron at each exon boundary
• join adjacent exons together

Question 23

Alternative splicing

Answer 23

• exons joined in different combinations to produce different mRNAs from the same gene
• different mRNA versions translated into different proteins with different functions
• more information can be stored in the DNA

Question 24

Transfer RNAs

Answer 24

• bring specific amino acids to ribosome
• cloverleaf shape
• bottom end contains anticodon sequence that pairs with codon in mRNAs
• top end contains amino acids

Question 25

Wobble hypothesis

Answer 25

61 different sense codons do not require 61 different tRNAs | -third nucleotide has more flexibility

Question 26

Aminoacylation

Answer 26

adds amino acid to tRNA

Question 27

Translation intiation

Answer 27

ribosome assembled with mRNA molecule and initiator methioneine-tRNA

Question 28

Translation elongation

Answer 28

amino acids linked to tRNAs added one at a time to growing polypeptide chain

Question 29

Translation termination

Answer 29

new polypeptide released from ribosome | -ribosomal subunits separate from mRNA

Question 30

Polysomes

Answer 30

multiple ribosomes can simultaneously translate a single mRNA

Question 31

Polypeptide processing

Answer 31

- removal of one or more amino acids from the protein chains - addition of organic groups - folding guided by chaperones

Question 32

Missense mutation

Answer 32

changes a sense codon to different sense codon

Question 33

Nonsense mutation

Answer 33

changes a sense codon to a stop codon

Question 34

Silent mutation

Answer 34

changes one sense codon to another sense codon that specifies the same amino acid

Question 35

Frameshift mutation

Answer 35

base-pair insertion of deletion alters the reading frame after the point of the mutation

Question 36

Spontaneous mutations

Answer 36

errors during DNA replication or repair

Question 37

Induced mutations

Answer 37

physical, chemical, and biological agents (mutagens) that generate mutations-mutagenesis