Chapter 17.1-17.3 - Transcription & RNA Processing

Question 1

Gene

Answer 1

A specific nucleotide sequence in DNA that directs protein synthesis for RNA molecules such as tRNA and rRNA

Question 2

Production of a protein from a gene requires what two processes?

Answer 2

Transcription and Translation

Question 3

Protein Synthesis in Prokaryotes

Answer 3

• no nucleus

- transcription and translation occur simultaneously and aren’t necessarily separate

Question 4

Polypeptide

Answer 4

A polymer consisting of a specific sequence of amino acids

Question 5

Protein Synthesis in Eukaryotes

Answer 5

-transcription and translation are spatially separate and include two things that prokaryotes don’t: processing and transport

Question 6

Transcription

Answer 6

The synthesis of RNA using information in the DNA. “Rewrites” DNA to make RNA. Binging site for RNA polymerase

Question 7

Initiation of Transcription (3)

Answer 7

1. Regulatory region “up stream” of beginning of gene. Also controls transcription initiation, timing, location and amount of gene expressed.
2. Coding sequence determines the sequence of amino acids in the protein

Question 8

Promoter

Answer 8

A specific DNA sequence of nucleotides.

*promoter is always before gene

Question 9

RNA Polymerase

Answer 9

• separates the two DNA strands

- catalyzes polymerization of RNA 5’3’

Question 10

3 parts of Transcription

Answer 10

1. Initiation
2. Elongation
3. Termination

Question 11

Template for Transcription (4)

Answer 11

1. Only one DNA strand is a template for RNA synthesis
2. For a given gene, same strand is always the template
3. Template strand is determined by orientation of promoter relative to gene
4. DNA and RNA have opposite ends:
   - RNA: 5’3’
   - DNA: 3’5’

Question 12

Complementary Base Pairing

Answer 12

• nitrogenous bases of mRNA are complementary to those of DNA template strand
• same base-pairing as DNA except A pairs with U
• RNA is anti-parallel to the template strand

Question 13

Translation

Answer 13

The process whereby the sequence of bases in mRNA is used to assemble a polypeptide

Question 14

Eukaryotic Cells Modify RNA after transcription (3)

Answer 14

1. Enzymes in nucleus modify pre-mRNA before it is transported to the cytoplasm.
2. During RNA processing, both ends or pre-mRNA are altered
3. Usually some interior parts of the molecule are cut out, and the other parts spliced together

Question 15

Modification of the ends of pre-mRNA (3)

Answer 15

1. Before export from nucleus, ends of mRNA are modified
2. Addition of a 5’ cap and 3’ poly A-tail
3. Modification performed by specific enzymes

Question 16

End of modification is required for (3)

Answer 16

1. Export of mRNA from nucleus
2. Protecting mRNA from degradation
3. Ribosome binding to the mRNA

Question 17

Capping the 5’ end of mRNA (5)

Answer 17

1. Cap is Guanosine Triphosphate
2. Added to the 5’ end of pre mRNA by a specific enzyme
3. Triphosphate linkage
4. A methyl Group is added to the cap
5. (7-methylguanosine)

Question 18

Polyadenylation of the 3’ end of mRNA (4)

Answer 18

1. A complex of specific proteins recognizes a polyadenylation signal near the3’ end of the pre-mRNA
2. Cleaves the 3’ end of pre-mRNA
3. Adds a long chain of adenine nucleotides to the 3’ end
4. Poly A tail
   * diagrams

Question 19

Introns and Exons in Eukaryotes

Answer 19

Introns: intervening sequences; transcribed but then removed

Exons: sequences that remain in the mRNA

DIAGRAMS

Question 20

Removal of Introns

Answer 20

1. Introns are removed by a large complex of proteins and RNA called splicesomes

Question 21

Spliceosome

Answer 21

Made up of snRNP (small nuclear ribonucleoproteins) and other small proteins.

*diagram

Question 22

snRNA (2)

Answer 22

• binds specific nucleotide sequences at the ends of intron via comp base pairing
• end of each intron are recognized by an snRNA

Question 23

Intron Splicing

Answer 23

• ends of introns are cut at the splice sites and Exons are joined together
• diagram!

Question 24

Why Introns? (2)

Answer 24

1. Some introns contain sequences that control gene expression and can encode more than one polypeptide
2. Depending on which segments are treated as Exons during splicing (this is called alternative RNA splicing)