Chapter 7: From DNA to Protein, How Cells read the Genome

Question 1

What does DNA sequence make a portion of in transcription

Answer 1

RNA, about 5% of sequence RNA

Question 2

Transcription produces RNA that…

Answer 2

is complimentary to one strand of DNA

Question 3

What do signals in DNA tell RNA polymerase to do?

Answer 3

Where to start and stop transcription

Question 4

What does EUkaryotic RNA polymerase require?

Answer 4

general transcription factors

Question 5

WHere are mRNAS processed in eukaryotes?

Answer 5

in the nucleus

Question 6

Transcription

Answer 6

flow of genetic information from DNA to RNA

DNA is transcribed into RNA by the enzyme RNA polymerase

Question 7

Genes

Answer 7

segments of DNA that are transcribed into RNA

Question 8

template strand

Answer 8

used to guide the synthesis of the RNA molecule

Question 9

coding strand

Answer 9

nontemplate strand of the gene (here, shown at the top) is sometimes called the coding strand because its sequence is equivalent to the RNA product

Question 10

Describe the process of DNA being transcribed into RNA by RNA polymerase

Answer 10

RNA polymerase moves stepwise along the DNA, unwinding the DNA helix in front of it. As it progresses, the polymerase adds ribonucleotides one-by-one to the RNA chain, using an exposed DNA strand as a template.

The resulting RNA transcript is thus single-stranded and complementary to the template strand

As the polymerase moves along the DNA template, it displaces the newly formed RNA, allowing the two strands of DNA behind the polymerase to rewind. A short region of hybrid DNA/RNA helix (approximately nine nucleotides in length) therefore forms only transiently, causing a “window” of DNA/RNA helix to move along the DNA with the polymerase.

Question 11

Function of mRNAs

Answer 11

-messenger proteins
- code for proteins

Question 12

Function of rRNAs

Answer 12

-ribosomal RNAs
- form the core of the ribosome’s structure and catalyze protein synthesis

Question 13

Function of miRNAs

Answer 13

-microRNAs
- regulate gene expression

Question 14

Function of tRNAs

Answer 14

-transfer RNAs
- serve as adaptors between mRNA and amino acids during protein synthesis

Question 15

Function of other noncoding RNAs

Answer 15

• used in RNA splicing, gene regulation, telomere maintenance, and many other processes

Question 16

What is the role of TFIIH in transcription?

Answer 16

• general transcription factor
• unwinds DNA
• phosphorylates RNA polymerase so that capping, splicing, and polyadenylation enzymes can bind and put on 5’ cap, splic out introns, and put on the poly A tail in the nucleus

Question 17

eukaryotic mRNA

Answer 17

has a cap at the 5ʹ end and a poly-A tail at the 3ʹ end. In addition to the nucleotide sequences that code for protein, most mRNAs also contain extra, noncoding sequences

The noncoding portion at the 5ʹ end is called the 5ʹ untranslated region, or 5ʹ UTR, and that at the 3ʹ end is called the 3ʹ UTR

Question 18

Introns

Answer 18

noncoding sequences

Removed from Pre-mRNAs by RNA Splicing (intervening sequences, removed in nucleus by splicesome)E

Question 19

Exons

Answer 19

gets translated to protein

protein coding sequences of most eukaryotic genes (exons) are interuppted by noncoding sequences(introns)

Question 20

What happens to mature eukayrotic mRNAs?

Answer 20

exported from nucleus

mRNAs are eventually degraded into the cytosol

Question 21

What structure carries out splicing of introns?

Answer 21

snRNPs

sense splice junctions; senses RNA portion of snRNP base pairs with sequences that signal splicing

proteins help form a loop to aid process

successful splices marked by exon junctions

Question 22

Specialized RNA-binding proteins

Answer 22

signals compelted mRNA is ready for export to the cytosol

Question 23

mRNA ready for export?

Answer 23

the 5’ cap and poly-A tail of a mature mRNA molecule are “marked” by proteins that recognize the modifications.

Once an mRNA is deemed “export ready,” a nuclear transport receptor (discussed in Chapter 15) associates with the mRNA and guides it through the nuclear pore. In the cytosol, the mRNA can shed some of these proteins and bind new ones,

Question 24

If a cell has a mutation that carries into low levels of transcription of mRNA from mutated transcription factor TFIIH, what would be the fate of the mRNA syntehsized?

Answer 24

would stay in nucleus

Question 25

Translation

Answer 25

flow of genetic information from RNA to proteins