Unit 2: Lecture 3

Question 1

How many protein coding genes does the human genome contain?

Answer 1

20, 000

Question 2

In molecular biology, what is a gene called?

Answer 2

transcription unit (ie. the sequence of DNA that produces a RNA transcript

Question 3

What does a sequence of nucleotides in DNA code for?

Answer 3

a single RNA molecule, along with the sequences necessary for its transcription

Question 4

What does a sequence of nucleotides in DNA usually contain?

Answer 4

promoter
RNA-coding sequence
terminator

Question 5

What is mRNA?

Answer 5

messenger RNA

• transcribed from DNA
• encodes protein (translated into a polypeptide chain in protein synthesis)
• considered “unstable” RNA

Question 6

What is RNase?

Answer 6

enzyme that degrades RNA, and are present everywhere

Question 7

What is the half-life of mRNA (when 50% of RNA is degraded)?

Answer 7

minutes for bacteria, hours for eukarya

Question 8

What do genes code for?

Answer 8

genes are templates for RNA synthesis

Question 9

What are the 3 types of RNA made from a gene?

Answer 9

mRNA (messenger RNA)
tRNA (transfer RNA)
rRNA (ribosomal RNA)

Question 10

Which type of RNA is the only RNA that encodes a protein?

Answer 10

mRNA

Question 11

What does tRNA do?

Answer 11

• considered as “stable” RNA
• folds to form 2° structures
• carries amino acids for translation

Question 12

What does rRNA do?

Answer 12

• considered as “stable” RNA

- complexes with proteins to make a ribosome

Question 13

What is a ribosome?

Answer 13

rRNA + protein

Question 14

What protects RNA from degradation?

Answer 14

the functions of tRNA and rRNA

Question 15

What sequences do genes have?

Answer 15

promoters and terminators

Question 16

What is a promoter?

Answer 16

• DNA sequence where regulatory proteins called transcription factors bind to recruit the RNA polymerase to start transcription of one DNA strand
• controls gene expression

Question 17

What do terminators do?

Answer 17

tell RNA polymerase where to stop transcribing

Question 18

How is a gene ‘read’?

Answer 18

from promoter sequence to terminator sequence

ie. the protein that transcribes (RNA polymerase) reads the gene starting around the promoter and moves along to the terminator

Question 19

What are transcription factors?

Answer 19

DNA binding proteins

Question 20

What do DNA binding proteins do?

Answer 20

• could bind in either major or minor grooves of DNA
• recognize specific sequences of base pairs, therefore R groups interacting with molecular groups on a GC base pair will be different than a AT base pair
• bind by H-bonds and other non-covalent interactions (ie. amino acid side chains (R groups) interact with the bases)

Question 21

What does how strongly a protein binds determine?

Answer 21

how long it will stay on the DNA strand and whether transcription will proceed

Question 22

What is transcription regulated by?

Answer 22

• how often RNA POL (with Sigma and/or other transcription factors) binds to the promoter
• how tightly transcription factors bind to the promoter

Question 23

What results in more RNA transcripts made from a particular gene?

Answer 23

binding more often and tightly

Question 24

How does the sequence of a promoter control gene expression?

Answer 24

different promoters can have different sequences but still can be recognized by transcription factors

Question 25

What are consensus sequences?

Answer 25

• calculated order of most frequent nucleotides (bases) found at each position in a sequence
• model for a DNA binding site
• conserved DNA sequences, they bind to transcription factors in promoters

Question 26

Do promoters from different genes have different DNA sequences?

Answer 26

yes, they can have similarities too

Question 27

What is a strong promoter?

Answer 27

promoters that are closer to consensus sequence will bind to transcription factors (and therefore RNA POL) MORE tightly (strongly) and MORE often

Question 28

What is a weak promoter?

Answer 28

promoters that are closer to consensus sequence will bind to transcription factors (and therefore RNA POL) LESS tightly (weakly) and LESS often

Question 29

What are weak vs. strong interactions?

Answer 29

non-covalent interactions between R groups on the protein and bases on the DNA

Question 30

DNA is transcribed to mRNA, which will be translated into a

protein. The sequence of the mRNA will include…

Answer 30

the complementary RNA sequence to the DNA starting with the transcription start site

Question 31

What is the template strand in DNA?

Answer 31

strand from 3’ to 5’

• base pairs are complementary to the template strand
• the opposite, non-template strand is anti-parallel to the template strand and is complementary to the template
• mRNA is complementary to the DNA template

Question 32

Why is the non-template strand sometimes called the ‘coding’ strand?

Answer 32

it resembles the mRNA that encodes the protein

Question 33

What are the upstream and downstream directions relative to?

Answer 33

promoter

polymerase reads genes in the 3’ to 5’ (promoter to terminator) direction on the template strand

Question 34

What is the upstream of the promoter direction?

Answer 34

towards 3’ end

Question 35

What is the downstream of the promoter direction?

Answer 35

towards 5’ end

Question 36

Where is the promoter found?

Answer 36

upstream of the terminator

Question 37

Where is the terminator found?

Answer 37

downstream of the promoter

Question 38

In genes encoding mRNA, what doe the coding sequence or coding region specify?

Answer 38

the amino acids of the protein

Question 39

What are the differences in bacterial and eukaryotic transcription/translation?

Answer 39

bacterial: same space and time
eukaryotic: DNA is enclosed in nucleus, transcription occurs in nucleus, translation occurs in cytoplasm