Lecture 18

Question 1

the central dogma of molecular genetics

Answer 1

• the directional flow of genetic information of DNA to RNA to protein

Question 2

2 genetic code: General features

Answer 2

• written in linear form using ribonucleotide bases that compose mRNA
• each “word” consists of three ribonucleotide letters, or a triplet code

Question 3

codon

Answer 3

every three ribonucleotides

Question 4

unambiguous

Answer 4

each triplet specifies only one amino acid

Question 5

degenerate

Answer 5

a given amino acid can be specified by more than one triplet codoon

Question 6

contains “start” and “stop” signals:

Answer 6

triplets that initiate and terminate translation

Question 7

commaless

Answer 7

once translation begins, codons are read with no break(s)

Question 8

nonoverlapping

Answer 8

any single ribonucleotide within mRNA is part of one triplet

Question 9

colinear

Answer 9

sequence of codons in a gene is colinear

Question 10

nearly universal:

Answer 10

a single coding dictionary is used by viruses, prokaryotes, archaea, and eukaryotes
- essentially all live uses the same building blocks

Question 11

mRNA - messenger RNA

Answer 11

• serves as intermediate in transferring genetic information from DNA to mRNA to protein
• genetic information is stored in DNA
• mRNA is the genetic code that translates protein from DNA

Question 12

triplet code

Answer 12

• provides 64 codons to specify 20 amino acids

Question 13

reading frame

Answer 13

• contigous sequence of nucleotides
• insertions or deletions shift reading frame and change codons downstream = frameshift mutation

Question 14

frameshift

Answer 14

reveals triplet nature code

Question 15

the effect of frameshift mutations…

Answer 15

on DNA sequences with the repeating triplet sequence GAG

Question 16

the insertion of a single nucleotide shifts all…

Answer 16

subsequent triplet reading frames

Question 17

the insertion of three nucleotides

Answer 17

changes only two triplets but the reading is then reestablished to the original sequence

Question 18

nonoverlapping

Answer 18

• genetic code reads three nucleotides at a time in continuous, linear manner
• during translation, genetic code is nonoverlapping

Question 19

the genetic code is…

Answer 19

degenerate
- many min acids specified by more than one codon
- only tryptophan and methionine are encoded by single codon
- genetic code shows order: chemically similar amino acids share one or two middle bases in triplets encoding them

Question 20

wobble hypothesis

Answer 20

• the initial two ribonucleotides of triplet codes are often more critical than the thrid

Question 21

third position ribonucleotide

Answer 21

• less spatially constrained
• need not adhere as strictly to established base-pairing rules

Question 22

methionine (AUG)

Answer 22

• initiator codon
• initial amino acid incorporated into all proteins
• in bacteria: modified form of methionine
• fmet

Question 23

termination codons:

Answer 23

• do not code for any amino acid
• are not recognized by tRNA

Question 24

translation terminates

Answer 24

• where termination codons are encountered

Question 25

Mitochondrial DNA

Answer 25

- revealed exceptions to universal genetic code - codon UGA normally specifies termination - mtDNA UGA codon encodes tryptophan in yeast and humans - Codon AUA normally specifies isoleucine - human mtDNA encodes internal insertion of methionine

Question 26

overlapping genes

Answer 26

- single mRNA has multiple initiation points - creates different reading frames - specifies more than one polypeptide

Question 27

ORF: open reading frame (overlapping genes)

Answer 27

- DNA sequence produces RNA with start and stop - series of triplet codons specify amino acids to make polypeptide

Question 28

in some viruses

Answer 28

initiation at different AUG positions out of frame with other AUG triplet codons leads to distinct polypeptides

Question 29

Iclicker question 2

Answer 29

know how to do