Chapter 10

Pre-mRNA must go through 3 processes before exiting a nuclear pore. These are:

1. Splicing

2. Capping

3. Polyadenylation

What occurs in splicing?

What occurs in capping?

What occurs in polyadenylation?

What relationship does the genetic code specify?

Relationship between the nucleotides in the mRNA and amino acids acids in polypeptides

How many start codons are there? Stop codons? What are they?

1 start codon (AUG), 3 stop codons UAA, UGA,UAG

T or F? Each amino acid has their own single codon. There is no redundancy.

False!

The structure of the mRNA consists of 4 parts. What are they?

• 1.

• 2.

• 3.

• 4.

1. ribosome binding

2. start codon

3. coding sequence

4. stop codon

What brings amino acids to the ribosome?

tRNA’s

tRNAs contain an _____ which is a 3 base sequence that is complementary to an ____ codon.​​

anticodon, mRNA

Are tRNAs different or are they the same? Why?

tRNA’s different because they have different anticodon sequences and carry different amino acids

Prokaryotic ribosomes are distinct from eukaryotic ribosomes, however, both share ______ ______ features.

common structural—> both have small and large ribosomal subunits

Ribosomes contain 3 discrete sites, what are they and what happens at each site?

• 1.

• 2.

• 3.

1. aminoacyl (A) site: where the charged tRNA (contains amino acid) enters, release factor also binds here when termination occurs

2. peptidyl (P) site: initiator tRNA binds here, tRNA present in the A site slides to the P site

3. Exit (E) site: uncharged tRNA exits

What is the difference between a chromosome and chromatin?

Chromosome: one discrete unit of genetic information, Chromatin: complex of DNA and proteins that make up EC (eukaryotic chromosome)

T or F? Chromosomes only have tight compaction states.

False; wrapping DNA around histone proteins to form nucleosomes, the basic unit of chromatin

Histone proteins contain a __ charge and DNA contains a _ charge. What causes these charges?

(+) and (-), histone proteins gain + charge from amino acids, DNA has - charge due to phosphate groups

Nucleosomes are organized into a more compact structure that is __ nm in diameter (second level of compaction).

30nm

What occurs in the third level of compaction?

Radial loops form

What is the difference between heterochromatin and euchromatin?

Heterochromatin: highly compacted chromosome

Euchromatin: loosely packed chromosome

What is a codon?

Triplet nucleotides that give a specific amino acid

Each codon represents one of the 20 ____ ____.

amino acids

What is the difference between transcription in bacteria and in eukaryotes? (Hint: think about where transcription occurs for each of them!)

Bacteria-

Location: cytosol

Initiation: uses sigma factor, 1 RNA polymerase is used

Eukaryotes-

Location: nucleus

Initiation: uses transcription factors, and RNA pol used

How does RNA polymerase know where to start when transcribing DNA?

recognizes the promoter

What are the four important sequences for transcription?

• 1.

• 2.

• 3.

• 4.

1. Promoter

2. Regulatory sequence: influences rate of transcription when regulatory proteins bind to it

3. Transcribed regions: region that contains the info

4. Termination: end of transcription

What is the difference between the template strand and the coding strand?

Coding strand: top strand, 5’ to 3’, same sequence as the mRNA, with the exception of U replacing T

Template strand: bottom strand, 3’ to 5’, the DNA strand that is transcribed into mRNA by RNA polymerase

Transcription occurs in 3 stages. What does each stage do?

1. Initiation: proteins help bring RNA polymerase to the promoter and DNA strands separate.

2. Elongation: RNA polymerase reads the DNA and synthesizes mRNA transcript. (RNA polymerase reads the template strand in the 3’ to 5’ direction and synthesizes mRNA transcript in the 5’ to 3’ direction)

3. Termination: RNA polymerase recognizes terminator and release the mRNA transcript and dissociates from DNA

Given the following DNA template strand, what is the correct mRNA sequence transcribed from it?

Template Strand (3' → 5'):
TAC GGA TCC GAT ACC

A. (5' → 3') AUG CCU AGG CUA UGG

B. (3' → 5') ATG CCT AGG CTA TGG

C. (5' → 3') UAC GGA UCC GAU ACC

D. (3' → 5') TAG GGT TCC GAT ACC

A. (5' → 3') AUG CCU AGG CUA UGG

Given the following DNA coding strand, what is the correct mRNA sequence transcribed from it?

Coding Strand (5' → 3'):
ATG CCT AGG CTA TGG

A. (3' → 5') AUG CCU AGG CUA UGG

B. (5' → 3') UAC GGA UCC GAU ACC

C. (3' → 5') TAC GGA TCC GAT ACC

D. (5' → 3') AUG CCU AGG CUA UGG

D. (5' → 3') AUG CCU AGG CUA UGG

If coding strand is 5’ to 3’, mRNA transcript will also be 5’ to 3’ —> same direction. 

Furthermore, the coding strand is the mRNA stand but thymine is replaced with uracil.

Given the following DNA template strand, what is the correct mRNA sequence transcribed from it?

Template Strand (3' → 5'):
GCT TAA CGG ATC GGA

A. (5' → 3') CGA AUU GGC UAA CCU

B. (3' → 5') CGA AUU GCC UAG CCU

C. (5' → 3') GCT TAA CGG ATC GGA

D. (3' → 5') GCU UAA CGG AUC GGA

E. (3' → 5') UCC GAU CCG UUA AGC

E. (3' → 5') UCC GAU CCG UUA AGC

(5’ to 3’) CGA AUU GCC UAG CCU (Flip it)

How does RNA polymerase find the promoter in bacteria? How does RNA polymerase find the promoter in eukaryotes? In eukaryotes, how many different types of RNA polymerase are there? What about prokaryotes?

1. promoter in bacteria—> sigma factor

2. promoter in eukaryotes—> transcription factors

3. 3 different types of RNA polymerase

4. 1 prokaryotes

RNA polymerase synthesizes mRNA in the __’ to __’ direction. If RNA polymerase reads the template strand in the 3’ to 5’ direction, which direction does it synthesize?

5’ to 3’ for both

What happens as RNA polymerase is finished synthesizing? (Hint: Do the strands come back together, do they not?)

DNA strands come back together 

How is mRNA similar and different from the coding and template strand? (Hint: Think about directionality and nucleotides!) 

mRNA is complimentary and anti-parellel to the template strand. mRNA is the same as the coding strand but T is replaced with U.