Translation

Question 1

How does the cell translate an mRNA message into a protein?

Answer 1

With the help of tRNA

Question 2

How many nucleotides does a tRNA consist of? Is it a single strand?

Answer 2

80

YES

Question 3

What is attached at the 3’ end of a tRNA?

Answer 3

an amino acid

Question 4

What is the anticodon of the tRNA? How long is it? What is it complementary to?

Answer 4

This is a 3 nucleotide sequence that is located on the other end relative to the amino acid

This pairs complementary with a codon on mRNA

Question 5

What is the function of aminoacyl-tRNA synthase?

Answer 5

This is an enzyme that matches and facilitates the binding of the amino acid to its appropriate tRNA molecule.

Question 6

What are the two recognition steps that must occur in order for translation to be accurate?

Answer 6

1. There must be a correct match between a tRNA and amino acid by the aminoacyl-tRNA synthase enzyme.
2. There must be a correct match between the anticodon of the tRNA to the mRNA codon.

Question 7

Look at this picture and have a basic understanding of how an amino acid is bound to tRNA.

Answer 7

Do it

Question 8

How do ribosomes work with tRNA and mRNA in protein synthesis?

Answer 8

They facilitate the coupling of tRNA anticodons with their complementary mRNA codons.

Question 9

What does a ribosome consist of?

Answer 9

Two ribosomal subunits: one large and one small

Ribosomal RNA (rRNA)

Question 10

What are the three binding sites a robosome has for tRNA and their basic function?

Answer 10

P - holds the tRNA that carries the growing polypeptide chain

A - holds the tRNA that carries the next amino acid to be added to the chain

E - the exit site, tRNA leave the ribosome at this site.

Question 11

Have an understanding of this picture of a ribosome with tRNA and mRNA attached.

Answer 11

DO IT

Question 12

What are the three stages of translation? Which two steps may require energy? What is used as the source of energy?

Answer 12

1. initiation (may use energy in form of GTP)
2. elongation (may use energy in form of GTP)
3. termination (use energy in form of GTP to dissociate ribosomal assembly)

Question 13

Do all three stages of translation require cofactors to aid in the process?

Answer 13

YES

Question 14

Describe the initiation stage of translation, this can be described in three steps.

Answer 14

1. a small ribosomal subunit binds with mRNA and a special initiator tRNA (has methianine attached)
2. the small subunit moves along the mRNA until it reached the start codon (AUG)
3. Initiation factors (proteins) bring the large subunit and initiator tRNA takes up the P site of the large subunit.

Question 15

Describe the process of elongation in regards to translation. This is also described in a series of 3 steps.

Answer 15

1. codon recognition - anticodon of incoming aminoacyl tRNA pairs with mRNA base sequence at the A site. (GTP hydrolysis makes this more efficient)
2. Peptide bond formation - carboxyl end of elongated strand of amino acids in P site tRNA forms peptide bond with the amino group of new amino acid in A site on its tRNA. At this point the elongated strand is briefly at the A site.
3. Translocation - robosome translocates the tRNA in the A site to the P site. At the same time the initial tRNA that was in the P site that is now empty of amino acids is moved to the E site where it is released. As the tRNAs are trnaslocated the mRNA moves alond with them because the tRNAs are bound to it. this exposes the next codon in the A site so the process can be repeated.

EACH ADDITION IS FACILITATED BY PROTEINS CALLED ELONGATION FACTORS.

Question 16

Describe the process of termination in translocation. This is also described in a 3 step sequence.

Answer 16

1. Ribosome reached stop codon on mRNA. The A site then accepts a release factor instead of a tRNA at this point.
2. The release factor hydrolyzes the bond between the P site tRNA and the last amino acid of its polypeptide chain. Freeing the polypeptide and tRNA from the ribosome.
3. The two ribosomal subunits and other components dissociate with the help of GTP hydrolysis

Question 17

Can multiple ribosomes translate the same mRNA simultaneously? What does this form? Is there an advantage to this?

Answer 17

YES

This is called a polyribosome.

The advantage is many polypeptides can be made very quickly.

Question 18

After translation, is a polypeptide chain ready to be considered a functional protein?

Answer 18

Most of the time, NO

They need to be modfied after translation

Question 19

What happens after a polypeptide becomes a completed protein?

Answer 19

They are targeted to a specific site in the cell.

Question 20

Does a polypeptide chain coil and fold into a 3D molecule with secondary and tertiary structure during and after its synthesis?

Answer 20

YES

Question 21

What dictates the primary structure of the proteins (polypeptide chain)? What effect does this have on the conformation of the protein?

Answer 21

The gene

The determination of the primary structure indirectly determines the conformation of the polypeptide chain.

Question 22

What are some examples of posttranslational modifications that may be required before proteins can do their job?

Answer 22

attachment of sugars, lipids, phosphate groups, etc..

Question 23

What are the two types of ribosomes that may be found in a cells? What are they based on?

Answer 23

Based on their location:

Free ribosomes - found in cytosol and mainly produce proteins that function and stay in the cytosol

Bound ribosomes - Bound to the ER or nuclear envelope and produce proteins of the endomembrane system and proteins that are secreted from the cell (insulin, etc)

Question 24

Can free and bound ribosomes switch roles? Does this mean they are identical?

Answer 24

YES and YES

free can become bound and bound can become free

Question 25

Where does polypeptide synthesis ALWAYS start?

Answer 25

In the cytosol

Question 26

If polypeptide synthesis always started in the cytosol, how do polypeptides that are meant for the endomembrane system or for secretion make their way to the ER?

Answer 26

They are marked by a signal peptide.

Question 27

How does a signal peptide move a beginning polypeptide chain and its ribosome to the ER?

Answer 27

SRPs or signal recognition particles bind to the peptide and brings the signal peptide and its ribosome to the ER.

Question 28

Describe the function of mRNA, tRNA, and rRNA.

Answer 28

mRNA - carries information for amino acid sequences of proteins from DNA to ribosomes. tRNA - serves as adapter molecule in protein synthesis and translated mRNA codons into amino acids rRNA - Plays catalytic (ribozyme) roles and structural roles in ribosomes.

Question 29

What is a primary transcript?

Answer 29

This is a precursor to mRNA, rRNA, and tRNA before it is cleaved by splicing or cleavage.

Question 30

What is small nuclear RNA snRNA?

Answer 30

Plays a structural and catalytic role in spliceosomes.

Question 31

What is SRP RNA?

Answer 31

This is a component of the signal recognition particle (SRP).

Question 32

What is the role of small nucleolar RNA (snoRNA)?

Answer 32

Aids in processing pre-mRNA transcripts for ribosome subunit formation in the nucleolus.

Question 33

What is the function of small interfering RNA (siRNA) and microRNA (miRNA)?

Answer 33

These are involved in the regulation of gene expression.

Question 34

What enables RNA to have such diverse functions like structural, informational, and catalytic (3)?

Answer 34

1. Can H-bond to other nucleic acids 2. Can assume a 3D shape 3. Has functional groups that allow it to act as a catalyst (ribozyme)

Question 35

What are two differences in the gene expression of prokaryotes vs. eukaryotes?

Answer 35

1. The nuclear envelope separates transcription from translation in eukaryotes, these two can happen simultaneously in prokaryotes. 2. Extensive RNA processing occurs in the nucleus before translation in eukaryotes. This does not occur in prokaryotes.

Question 36

What is the definition of a mutation?

Answer 36

Changes in the genetic material of a cell or virus.

Question 37

What is a point mutation?

Answer 37

This is a chemical change in just one base pair of a gene.

Question 38

What is it called when a mutation has an adverse effect on the phenotype of the organism?

Answer 38

Genetic disorder, or a hereditary disease

Question 39

Can even changing one base pair lead to an abnormal protein to be produced?

Answer 39

YES

Question 40

Understand this picture of a point mutation.

Answer 40

DO IT.

Question 41

A point mutation can be divided into two different categories, what are they?

Answer 41

Base-pair substitutions Base pair insertions or deletions

Question 42

In the point mutation category that is base-pait substitutions, what does this refer to and what three sub-categories of mutation can occur?

Answer 42

This is the replacement of one nucleotide and its partner with another pair of nucleotide. 1. Silent mutation - No effect on encoded protein due to redundancy of genetic code (multiple codons for same amino acid) 2. Missense mutation - still codes for an amino acid, but not the right amino acid. 3. Nonsense mutation - changing amino acid codon to a stop codon, nearly always lead to a nonfunctional protein.

Question 43

In regards to base-pair insertions or deletions point mutations, what are they are what do they cause?

Answer 43

The addition or loss of nucleotide pairs in a gene. These often have a much more disasterous effect on the resulting protein than base pair substitution mutations do. They cause a shift in the READING FRAME, which leads to a FRAMESHIFT MUTATION

Question 44

While some mutations are spontaneous, others are caused by physical or chemical agents. What are these agents called?

Answer 44

Mutagens.

Question 45

What is a gene?

Answer 45

A region of DNA whose final product is either a polypeptide or an RNA molecule.