Chapter 4 - Nucleic Acids

Question 1

What are the features of the genetic code?

Answer 1

1. Triplet code
2. Widespread
3. Incomplete
4. Non-overlapping
5. Degenerate
6. Universal / Unambiguous

Question 2

Why is the genetic code triplet code?

Answer 2

• Triplets can be codons
• Each triplet codes for one anmino acid

Question 3

Why is the genetic code widespread?

Answer 3

-A triplet can code for a specific amino acid in all organisms
- But some variations exist

Question 4

Why is the genetic code incomplete?

Answer 4

• Some codons do not code for an amino acid
• But they mean stop, to stop the synthesis of the ppc
  e.g. UAG

Question 5

Why is the genetic code non-overlapping?

Answer 5

• Each triplet is read separately
• Each base is only part of one triplet

Question 6

Why is the genetic code degenerate?

Answer 6

• More than one triplet codes for many of the amino acids
• Some codons do not code for any amino acids
• Gives protection against mutations
• Because some substitution mutations can result in the same amino acid being coded for (silent mutation)

Question 7

Why is the genetic code universal/unambiguous?

Answer 7

The code is the same in almost all organisms

Question 8

Describe and explain the features of the genetic code.

Answer 8

• Triplet code; each triplet can also act as a codon and codes for one amino acid
• Widespread; each triplet can code for the same amino acid for all organisms but variations exist
• Incomplete; some codons do not code for an amino acid but mean stop
• Non-overlapping; each triplet is read separately and each base is only part of one triplet
• Degenerate; more than one triplet codes for many of the amino acids or some codons do not code for any aas, also gives protection against mutations
• Universal; the code is the same in almost all organisms

Question 9

What is a triplet?

Answer 9

3 DNA nucleotide bases on the CODING STRAND of DNA

Question 10

What is a codon?

Answer 10

3 RNA nucleotide bases found in mRNA after transcription

Question 11

What is an anticodon?

Answer 11

3 RNA nucleotide bases found at the BASE of the HAIRPIN of tRNA

Question 12

What is the function of DNA?

Answer 12

To carry genetic information; also contains exons and introns

Question 13

What is the specific pentose sugar of DNA?

Answer 13

Deoxyribose

Question 14

What are the bases in DNA?

Answer 14

adenine, thymine, guanine, cytosine

Question 15

How many polynucleotide strands does DNA have?

Answer 15

2

Question 16

What is the typical length of a DNA molecule?

Answer 16

hundreds of thousands of DNA nucleotides

Question 17

What is the function of mRNA?

Answer 17

To carry genetic information FROM NUCLEOPLASM TO CYTOSOL

Question 18

What is the function of tRNA?

Answer 18

To carry a specific amino acid to RIBOSOME during translation

Question 19

What is the function of rRNA?

Answer 19

To provide a binding site for mRNA during translation

Question 20

What is the specific pentose sugar for the RNAs?

Answer 20

Ribose

Question 21

What are the bases found in RNA?

Answer 21

adenine, uracil, guanine, cytosine

Question 22

How many polynucleotide strands are in RNA?

Answer 22

1

Question 23

What is the typical length of an mRNA molecule?

Answer 23

typically 2000 RNA nucleotides

Question 24

What is the typical length of a tRNA molecule?

Answer 24

typically 80 RNA nucleotides

Question 25

What is the typical length of an rRNA molecule?

Answer 25

varies

Question 26

Which nitrogenous bases are purines?

Answer 26

adenine, guanine

Question 27

Which nitrogenous bases are pyrimidines?

Answer 27

uracil, thymine, cytosine

Question 28

What is the purpose of protein synthesis?

Answer 28

To **produce a SPECIFIC POLYPEPTIDE CHAIN**

Question 29

Which molecules are involved in protein synthesis?

Answer 29

- exposed gene - **activated** RNA nucleotides - mRNA - **activated** tRNA - amino acids - ribosomes - RNA polymerase - *peptidyl transferase (in ribosome large subunit)*

Question 30

What are the two phases of protein synthesis and where do they take place?

Answer 30

1. **transcription** in the _nucleoplasm_ 2. **translation** in the _ribosome_

Question 31

Describe the process of protein synthesis

Answer 31

1. _Transcription occurs in the nucleoplasm_ **RNA is transcribed from a DNA template** 2. _RNA is processed_ The **RNA transcript is spliced and modified to produce mRNA**, mRNA moves **from nucleus to cytoplasm** 3. **mRNA leaves nucleus via _nuclear pore_ and attaches to a ribosome** 4. _Amino acids are activated_ Each amino acid **attaches to its proper tRNA** with the help of a **specific enzyme and ATP** 5. _Translation occurs in a ribosome_ **A succession of tRNAs ADD THEIR AMINO ACIDS to the ppc** as mRNA is moved through the ribosome **one codon at a time** 6. _When completed, the ppc is released from the ribosome._

Question 32

What are the subunits of a ribosome made of?

Answer 32

rRNA and proteins **Large** subunit contains **peptidyl transferase**

Question 33

How is tRNA activated?

Answer 33

specific amino acid is joined to tRNA by an enzyme to produce activated tRNA

Question 34

What are the features of a tRNA molecule?

Answer 34

- has **complementary base pairing** - has **hydrogen bonds and an ester bond with amino acid** - RNA polynucleotide chain **folds in on itself** - **ANTICODON determines which specific amino acid is carried**

Question 35

Where is the amino acid attached to in a tRNA molecule?

Answer 35

The 3" end