Chapter 17 - From Gene to Protein

Question 1

What is Transcription?

Answer 1

creating an RNA copy of a DNA code

Question 2

What does Transcription consist of?

Answer 2

Initiation - the beginning of the copying
Elongation - the creation of the RNA copy
Termination - the end of the copy

Question 3

What happens in initiation?

Answer 3

The promoter (a section of DNA often includes a TAT box and ~25 nucleotides upstream from the start point) of a gene includes within it the transcription start point.

• Transcription factors attach to the TATA box
• then an RNA polymerase II binds to the promoter after transcription factors are present and attached to the TATA box.
• The RNA polymerase II will separate the two DNA strands and will make a copy of RNA

Question 4

What are the components of the Transcription Initiation Complex?

Answer 4

Promoter, Transcription factors, RNA Polymerase II and the other transcription factors that bind to the DNA when RNA polymerase II binds.

Question 5

What is the elongation process?

Answer 5

The RNA Polymerase II will move along the DNA strand, it will unzip the double helix.

• RNA nucleotides are bound together from 5’ to 3’ making a copy of the DNA
• remember that in RNA, Thymine is replaced with Uracil

Question 6

How is transcription terminated?

Answer 6

The RNA polymerase II will transcribe a sequence on the DNA called the Polyadenylation signal sequence

• then at ~a0-35 nucleotides downstream from the AAUAAA, proteins associated with the growing RNA will cut it free from the polymerase.
• releases a pre-mRNA for processing

Question 7

What happens in RNA processing?

Answer 7

After RNA is transcribed a modified guanin nucleotide is added to the 5’ end called the 5’ cap.
- At the 3’ end an enzyme adds 50-250 more adenine nucleotides forming what is called the poly-a-tail.

Question 8

How does a copy of RNA turn into a mRNa (messenger RNA)?

Answer 8

when an RNA copy is made there are regions made up of coding and non-coding regions. Non-coding regions need to be cut out.

• The coding regions are called Exons and the non-coding regions are Introns
• When the 5’ cap, Poly-A tail, and the introns are removed the molecule becomes a messenger RNA.

Question 9

Translation consists of…

Answer 9

mRNA that has the genetic code that will be made into proteins.

• Transfer RNA (tRNA) is a folded up piece of RNA that binds to amino acids to transfer them to the new protein
• Ribosomes act as a work bench for the adding of amino acids into a polypeptide chain.

Question 10

What are tRNA?

Answer 10

RNA that is folded up (typically three times).

It will have an attachment site on one end with a genetic code that matches with an amino acid.

Question 11

What is an Anticodon?

Answer 11

the nucleotides that are exposed from one of the three loops in the tRNA.

Question 12

What is an aminoacyl-tRNA synthetase?

Answer 12

It is an enzyme that binds an amino acid to a tRNA molecule

Question 13

What are tRNA and amino acid that are bound together called?

Answer 13

Aminoacyl tRNA (sometimes called “charged tRNA)

Question 14

What happens to the charged tRNA?

Answer 14

It will wait until the bound amino acid is needed in the ribosome to make the polypeptide.

Question 15

What function does the ribosome have in translation?

Answer 15

• The ribosome acts as a workbench for translation of the mRNA into a polypeptide chain.

Question 16

What composes the ribosome?

Answer 16

The small subunit - Has a binding site for the mRNA
The Large subunit - Has a site for the Aminoacyl tRNA to enter, a site where the amino acids are bound to each other, and an exit site where the tRNA leaves the ribosome.
Exit tunnel - where the growing polypeptide chain leaves.

Question 17

What is the initiation process in Translation?

Answer 17

The mRNA is bound to the small ribosomal subunit.

• Every three nucleotides are codons with specific codes to make amino acids.
• An initiator tRNA will bind to a codon AUG with UAC to start the process.
• The large subunit is then added and completes the Translation Initiation Complex.
• This process also requires initiation factors and energy from GTP

Question 18

What is the elongation process of Translation?

Answer 18

• A codon in site A will bind to a tRNA with the corresponding code.
• a peptide bond will form between the amino acids
• Moves from Site A to P to E and out of the ribosome.
• Then repeated until the polypeptide is complete.

Question 19

What is the Termination process of Translation?

Answer 19

• At the end of the mRNA sequence for the polypeptide there will be a stop codon (UAG, UAA, UGA)
• a release factor that is similar to a tRNA is accepted and bound to the codon.
• The release facto promotes hydrolysis of the bond between tRNA and the last amino acid
• This will free the peptide from the ribosome
• With hydrolysis of at least 2 GTP the ribosome subunits and mRNA are dissociated.

Question 20

What is the start codon?

Answer 20

AUG

Question 21

What are the stop codons?

Answer 21

UAA, UGA, UAG

Question 22

What are mutations?

Answer 22

They are changes to the genetic information

Question 23

What are the different type of mutations?

Answer 23

Point mutations, Insertions, Deletions, Frameshift mutation

Question 24

What are the different types of point mutations?

Answer 24

Silent - No effect on amino acid sequence
Missense - Changes amino acid for another amino acid (may have little effect
Nonsense - change from an amino acid codon for a stop codon

Question 25

What is an Insertion mutation?

Answer 25

An addition of nucleotide pairs

Question 26

What is a Deletion mutation?

Answer 26

The loss of nucleotide pairs

Question 27

What is a Frameshift mutation?

Answer 27

With and insertion of deletion of nucleotide pairs it can alter the reading frame of the genetic code.