Lecture 18

Question 1

What is Transcription?

Answer 1

A DNA segment into RNA.

Question 2

DNA components vs RNA components?

Answer 2

DNA: 2-Deoxyribose Sugar and Thymine base

RNA: Ribose Sugar and Uracil base

Question 3

Messenger RNA (mRNA)

Answer 3

500-10,000 nucleotides. Information to transport into proteins (genes). 5’ and 3’ untranslated regions carry features involved in initiating and terminating translation.

Although, Bacterial genes are 1kb long, mRNA can be longer due polycistronic.

Question 4

What is Polycistronic?

Answer 4

The ability in of mRNA to encode several genes on the same RNA sequence.

Question 5

Introns

Answer 5

Non-coding regions found in Eukaryotes –> size of >10kb in size. Get spliced out and removed before translation.

Question 6

Transfer RNA (tRNA)

Answer 6

75-100 kb in size. Form secondary structures. that role is to deliver amino acids to the ribosomes. Has an anticodon which matches up with mRNA.

Question 7

Ribosomal RNA (rRNA)

Answer 7

Structural components of ribosomes (1500-1900 (small subunits) or 2900-4700 (large subunits))

Eukarya - 80 S Ribosome: small 40S subunit + large 60S subunit

Bacteria - 70S Ribosome: small 30S subunit + large 50S subunit

Question 8

Promoter

Answer 8

Direct RNA polymerase to initiate transcription at specific DNA positions.

Question 9

Bacterial Promoters

Answer 9

Elements bound by sigma factors upstream of where transcription is initiated (ex. -10/-35). Direct RNA polymerase to promoter.

Question 10

Alternative Sigma Factors

Answer 10

Direct RNA polymerase to different gene sets important in different conditions. –> co-regulated genes (ex. heat stress –> start to cool)

Question 11

Eukarya Promoters

Answer 11

Several different elements bound to several different transcriptional factors to direct the initiation of transcription.
i.e. TATA binding protein (-20), GC box, CAAT box, Octamer box. (all upstream to where transcription begins)

Transcriptional factors (TBP, TFIIB) bind to upstream elements, one RNA pol directed to transcription site.

Question 12

How many RNA polymerase does bacteria have?

Answer 12

One

Question 13

How many RNA polymerase does eukaryotes have?

Answer 13

Three

Question 14

What does TBP stand for?

Answer 14

TATA-binding protein that interacts with TATA box element in eukarya.

Question 15

What is TFIIB role?

Answer 15

Additional transcription factor in eukarya that binds to the promoter region.

Question 16

How many RNA polymerase does Archaea (similar to eukarya) have?

Answer 16

One

Has TBP and TFB transcriptional factors that interact with the promoter in TATA box.

Question 17

How is bacteria transcription terminated?

Answer 17

Rho protein, makes RNA polymerase “pop-off” at specific DNA site.

OR Rho-Independent Termination where a hairpin structure forms complementary RNA stretches (G and C rich, followed by U segment)

Question 18

How is eukaryotic transcription terminated?

Answer 18

Depends on RNA polymerase. RNA is modified after termination in eukarya: 5’ 7-methylguanosine cap added, 3’ poly A tail, Introns spliced out (exons are joined).

Question 19

Translation in Bacteria

Answer 19

Transcription and Translation are coupled, they have spontaneously due to lack of nuclear membrane.

Question 20

Charged tRNA interaction with mRNA

Answer 20

Assemble amino acids in a particular order. The tRNA anticodon corresponds to mRNA codon in sequence. Amino Acids delivered by tRNA build peptide bonds.

Question 21

How many codons are there?
How many amino acids are there?
Start codon?
Stop codons?

Answer 21

64 codons. 20 amino acids.

Several codons for each amino acid, 3rd nucleotide is “wobble codon” meaning it usually leads to the same amino acid.

Start codon = AUG (Met)

Stop codons = UAA, UAG, UGA (Stop)

Question 22

How are tRNA charged?

Answer 22

tRNA synthetase enzymes that attach amino acids to specific tRNA with matching anti-codons

Question 23

Bacteria Interaction with rRNA (BOTTOM)

Answer 23

Interaction between Shine-Delgarno sequence (ribosome binding site) and specific site in 16S rRNA in small ribosomal subunit.
The 16S rRNA is complementary to the Shine-Delgarno sequence.

Question 24

Polycistronic in Bacteria

Answer 24

Uses multiple shine-delgarno sequences on same mRNA to encode for multiple proteins.

Question 25

What are the 3 sites? (Eukaryota Monocistronic)

Answer 25

A, P, and E sites

Charged tRNA’s enter A site, peptide bond formed in P site, and uncharged tRNA (lacking an amino acid) exits in E site. Ribosome moves along mRNA (only one), polypeptide released when stop codon is reached. Uses release factors (same in bacteria) for complex to fall apart at stop codon.

Question 26

Chaperones

Answer 26

Amino acid side groups (R groups) which assist in folding proteins after leaving the ribosome. Allow correct folding.

Question 27

Which group is often modified by the addition of chemical groups?

Answer 27

Eukaryal proteins

Question 28

Protein Modification

Answer 28

Proteins with different chemical groups or carbohydrates can have affected folding. This can serve to activate or inhibit protein function.

Question 29

What directs proteins to appropriate cellular locations?

Answer 29

Single Peptides (short AA sequences at N-terminus)