Unit 4 - DNA + Protein Synthesis

Question 1

Describe DNA in prokaryotes/Chloroplasts + Mitochondria?

Answer 1

-Circular DNA
-Shorter than eukaryotic DNA
-Not associated with histone proteins
-Do not form chromosomes
-Some have plasmids
-No introns

Question 2

Describe DNA in eukaryotes?

Answer 2

-Linear DNA
-Longer than prokaryotic DNA
-Associated with histone proteins
-Forms chromosomes
-Contains introns

Question 3

What is the function of DNA?

Answer 3

It is to code for polypeptides.

Question 4

Definition of a gene?

Answer 4

It is a base sequence of DNA that codes for either the amino acid sequence of a polypeptide or a functional RNA (including rRNA AND mRNA)

Question 5

What is a triplet?

Answer 5

3 bases in DNA that code for 1 specific amino acid

Question 6

What are introns?

Answer 6

Non-coding sections of DNA.
Non-coding repeats are found between genes in multiple repeats.

Question 7

What are exons?

Answer 7

Coding sections of DNA within a gene. Separated by non-coding sections.

Question 8

Why is genetic code universal, non-overlapping and degenerate?

Answer 8

Universal-in all organisms, each specific triplet codes for the same amino acid.
Non-overlapping-each base is part of only one triplet/only read once.
Degenerate-more than one triplet codes for each amino acid.

Question 9

Definition of genome?

Answer 9

The complete set of genes in a cell.

Question 10

Definition of proteome?

Answer 10

The full range of proteins that a cell is able to produce.

Question 11

Differences between DNA nucleotides and RNA nucleotides?

Answer 11

DNA:consists of a phosphate group/deoxyribose sugar/Adenine, Thymine, Guanine + Cytosine/double helix/2 polynucleotide strands held together by hydrogen bonds between base pairs.

RNA:consists of a phosphate group/ribose sugar/Adenine, Uracil, Guanine + Cytosine/single helix/1 polynucleotide strand.

Question 12

What are the 3 types of RNA?

Answer 12

1) Messenger RNA (mRNA)
2) Transfer RNA (tRNA)
3) Ribosomal RNA (rRNA)

Question 13

What is mRNA?

Answer 13

This is a single stranded, linear polynucleotide chain.
It is a copy of a single gene on the DNA. Its length will depend upon the number of bases that make up the gene, so much shorter than DNA.
The sequence of bases on the mRNA is complementary to the sequence of bases on the DNA strand.

Question 14

What is a codon?

Answer 14

A sequence of 3 based on a molecule of mRNA. Each codon codes for 1 amino acid.

Question 15

What is tRNA?

Answer 15

It consists of 1 single stranded polynucleotide chain. It has hydrogen bonds between areas of the same strand, giving it a cloverleaf shape. It has an amino acid binding site where only one specific amino acid will bind to it.

Question 16

What is an anticodon?

Answer 16

Opposite to the amino acid binding site, it has a region of 3 bases known as an anticodon. Its anticodon has a complementary sequence to the codon on the mRNA. The anticodon is specific to the amino acid carried by the tRNA.

Question 17

Role of the tRNA molecule?

Answer 17

It is to carry a specific amino acid to the ribosome for protein synthesis.

Question 18

3 processes involved in protein synthesis?

Answer 18

1) Transcription
2) Splicing
3) Translation

Question 19

Where does transcription occur?

Answer 19

Occurs in the nucleus of eukaryotic cells.

Question 20

Difference between transcription in prokaryotes and eukaryotes?

Answer 20

In prokaryotes, transcriptions results directly in the production of mRNA not pre-mRNA as they have no introns.

Question 21

What is the process of transcription?

Answer 21

-An enzyme attaches to and unwinds DNA double helix at site to be transcribed.
-Hydrogen bonds between the 2strands are broken causing the DNA strands to separate.
-1 strand is used as a template.
-Free RNA nucleotides join with exposed DNA bases via complementary base pairing on the template strand: U-A A-T C-G G-C
-The enzyme RNA polymerase joins free RNA nucleotides together forming phosphodiester bonds forming pre-mRNA which contains introns and exons.
-Introns are removed through splicing, leaving a molecule of mRNA.
-mRNA passes out of nucleus via nuclear pore and goes to ribosome.

Question 22

Process of translation?

Answer 22

-mRNA attaches to the ribosome. 2 codons fit into the ribosome at any one time.
-tRNA carrying a specific amino acid binds to the 1st codon on mRNA, via complementary base pairing with its anticodon (U-A A-T C-G G-C)
- A 2nd tRNA carrying a specific amino acid binds to the 2nd codon on mRNA, via complementary base pairing with its anticodon.
-Enzymes join amino acids together forming peptide bonds, using energy from the hydrolysis of ATP.
-Ribosome moves along mRNA to the next codon.
-The tRNA is removed from 1st codon, which goes to collect another of the same amino acid from the cytoplasm.
-A 3rd tRNA carrying a specific amino acid binds to the 3rd codon on mRNA, via complementary base pairing with its anticodon and a new peptide bond forms between the amino acids.
-This process repeats, until the stop codon is reached, when the polypeptide then detaches from the ribosome.