Ch. 17 Transcription and Translation

Question 1

2 main processes of Gene Expression

Answer 1

Transcription: making complimentary copy of 1 strand of DNA

Translation: using the mRNA sequence to direct protein synthesis

Question 2

Why do different cells do different stuff if they all have the same instructions?

Answer 2

 SELECTIVE READING OF DNA = GENE EXPRESSION!
 Cells do not have to use all instructions all the time

Question 3

2 side processes of Gene Expression

Answer 3

 RNA processing

 Post-transitional modification
* Folding, glycosylation, transport, activation, degradation of protein
* Looks much different than what we began with!

Question 4

Gene Expression’s 3 types of RNA? What does gene expression require?

Answer 4

mRNA, rRNA, and tRNA

gene expression requires RNA polymerase enzymes for transcription and ribosomes for translation

Question 5

mRNA

Answer 5

single strand, leaves nucleus and finds ribosome in cytoplasm

Question 6

rRNA

Answer 6

allows ribosomes in reading the mRNA; made in nucleolus

Question 7

tRNA

Answer 7

can transport amino acids; need rRNA to bring amino acids to them to build proteins

Question 8

Transcription in Bacteria (A PROKARYOTE!!)

Answer 8

No nucleus, transcription and translation happen in cytoplasm, Bacteria transcription involves more than RNA and DNA

The enzyme RNA Polymerase binds to Sigma Protein to form Holoenzyme

How do we know which ones will be transcribed of DNA?
* Promotor region!
o Indicates where sigma is to bind(upstream from start of transcription, -35 box TTGACA and -10 box TATAAT)
o Boxes tell how far you are from binding site
o Example: like sign post being a few miles from somewhere on a road trip

Question 9

3 steps of Gene Transcription

Answer 9

Initiation, Elongation, and Termination

Question 10

Initiation Phase

Answer 10

RNA Polymerase opens Transcription Bubble

Sigma binds to promoter region of DNA; The promoter region serves as a recognition site for RNA polymerase and is usually located upstream of the gene that is to be transcribed

Sigma only binds in one
orientation, which determines
template strand and direction of
transcription

Question 11

Elongation

Answer 11

RNA Pol will read the template strand 3’-5’, and
write a complementary mRNA in the 5’-3’ direction

Question 12

Termination

Answer 12

Once RNA polymerase has transcribed the entire gene(mRNA), it reaches a termination site on the DNA template. The termination site signals the end of transcription

Two regions of transcribed mRNA contain lots
of Gs and Cs, which bond with each
other to form a “hairpin” loop

Hairpin causes RNA Polymerase to separate from mRNA transcript
(This mechanism not fully understood)

Question 13

Differences of Transcription in EUkaryotes

Answer 13

Transcription and translation are separated(nucleus vs cytoplasm)

Initiation complex: use transcription factors instead of sigma to initiate transcription(binds to TATA box, the part of the core promoter, and other factors join to build complex)

mRNA MOdfication

Question 14

Modifications of Eukaryotic mRNA

Answer 14

5’ untranslated to 3’ untranslated region is the coding region

5’ capping: Happens after TRANSCRIPTION!!! Prevents degradation by enzymes, enables ribosome binding

3’ poly A signal: imbedded in to mRNA, indicates termination of mRNA production, no hairpin loops in eukaryotes; and tail – added after transcription, prevents degradation by enzymes

Question 15

Introns and Exons

Answer 15

DNA contains strands of nucleotides that are referred to as exons and introns

Exons: coding regions of eukaryotic genes that will be part of the final mRNA product

Introns: intervening noncoding sequences that will not be in the final mRNA

Question 16

Intron Splicing

Answer 16

removes introns from Primary RNA transcripts

Catalyzed by small nuclear ribonucleoproteins, snRNPs; Binds to start and end of introns and branch site within the intron

More snRNPs assemble the splicesome; Forms temporary complex; Over 200 proteins, most complex macromolecular machine

intron cut from exon, released and exons are joined together

 splicing allows different mRNAs and proteins to be produced from a single gene

Question 17

Alternative Splicing

Answer 17

1 gene can yield many mRNA/protein combos

Exons can be pulled out and make multiple different proteins out of single stretch of DNA depending on how mRNA is modified for sequence

Not known if they can change order, but keep it this way in mind for now

Question 18

Translation

Answer 18

• using mRNA sequence to direct amino acid sequence

Question 19

Transfer RNA- tRNA

Answer 19

Anticodon to match each of the possible codons

Each tRNA has an anticodon(complimentary to mRNA) and an attachment site for a specific amino acid

Remember, when reading the Genetic code, you(much like the ribosome) read the mRNA condons

Question 20

Initiation, Elongation, and Termination of Translation

Answer 20

Initiation:
When mRNA binds small ribosomal subunit, a “start” codon signals the ribosome to attach a tRNA carring
Met. Large subunit attaches, translation begins.

Elongation:
mRNA slides through ribosome, next tRNA brings in
2nd amino acid. Peptide bond is formed.
* Used (empty) tRNA are spit out of the “E” site. - New tRNA enters into the “A” site

Note that when peptide bond forms, the protein is
now connected to the tRNA in the A site

Termination
A “Stop” codon carrying a release factor enters “A” site.
* No amino acid, triggers breakup of ribosomal
complex

VISUALS ON SLIDES WILL HELP!!!!