DNA, genes and protein synthesis - Chapter 8

Question 1

What is a gene ?

Answer 1

A section of DNA that codes for a specific sequence of amino acids which make up the primary structure of a protein

Question 2

Allele ?

Answer 2

Alternative form of a gene

Question 3

Name the 4 features of a genetic code?

Answer 3

1. It is a triplet code
2. It is a degenerate code
3. It is a non-overlapping code
4. It is a universal code

Question 4

What does triplet code mean?

Answer 4

3 bases that codes for one amino acid

Question 5

What is a codon?

Answer 5

3 bases ( a triplet)

Question 6

What is a degenerate code?

Answer 6

When more than one triplet codes for an amino acid

Question 7

What is a non-overlapping code?

Answer 7

Look at notes for example

Each base appears in one triplet , only read each base one

Question 8

What is a universal code ?

Answer 8

The same codon always codes for the same amino acid

Question 9

What is transcription (definition)?

Answer 9

The process of producing pre-mRNA using a sequence of DNA as a template

Question 10

Where does transcription take place?

Answer 10

In the nucleus

Question 11

What is splicing (definition) ?

Answer 11

The process of removing introns from pre-mRNA because they don’t code for an amino acid

Question 12

Where does splicing take place ?

Answer 12

In the nucleus

Question 13

What is translation ?

Answer 13

The production of a polypeptide chain

Question 14

Where does translation take place?

Answer 14

In the ribosomes

Question 15

What is mRNA (messenger RNA) ?

Answer 15

Copy of a gene used to code for a polypeptide

Question 16

What is tRNA (transfer RNA) ?

Answer 16

A clover- leaf shaped sequence of bases. It carries amino acids during translation.

Question 17

What is rRNA (ribosomal RNA) ?

Answer 17

A primary component of ribosomes

Question 18

Transcription steps?

Answer 18

1. DNA in the nucleus
2. DNA helicase breaks the hydrogen bonds
3. RNA polymerase binds to the start of a gene (section of DNA) and unwinds the double helix, exposing one of the template strands.
   4.Free RNA nucleotides bind to free DNA nucleotides on template strand via complementary base pairing. Adenine to uracil, and cytosine to guanine.
   This is formed via phosphodiester bonds in a condensation reaction (due to RNA polymerase)
4. Behind the RNA polymerase, the DNA rejoins into a double helix
5. RNA polymerase reaches a terminator ( a stop codon ), the chain is terminated, the pre- mRNA detaches and double helix reforms
6. Introns are removed due to splicing, so mRNA is formed.

Question 19

What are exons?

Answer 19

Coding regions

Question 20

What are introns?

Answer 20

Non -coding regions

Question 21

Splicing steps?

Answer 21

Spliceosome forms and causes the introns to form loops which allows exons to be joined under the loop, and allows the introns to be removed.

Question 22

Splicing occurs in _______ cells, but not ________ cells. Why?

Answer 22

Splicing occurs in eukaryotic cells, but not in prokaryotic cells. This is because the RNA produced in eukaryotes has introns. But prokaryotic cells do not have introns when RNA is produced

Question 23

What is a histone ?

Answer 23

Proteins that the DNA coils around forming supercoils, which makes DNA more compact

Question 24

Prokaryotic vs Eukaryotic DNA

Answer 24

Prokaryotic : short, circular DNA molecules, not associated with proteins (no histones)
Eukaryotic: long, linear DNA molecules, associated with proteins (has histones)

Question 25

Translation steps?

Answer 25

After splicing, mRNA attaches to the ribsome ( no longer pre-mRNA)

1. tRNA carries amino acids to the ribosome
   Each tRNA has an anticodon (a triplet of RNA bases) that is complementary to a codon on the mRNA strand
2. The mRNA attaches to the ribosome. Specific tRNA molecule for specific amino acid
3. The mRNA will be fed through the ribosome and the RNA bases are read in sequence
4. The amino acids are carried to the ribsome by tRNA, and the anticodon on the tRNA attach to complementary bases on the mRNA. The amino acids become connected by peptide bonds and are released as a chain.
   ATP is required to make these peptide bonds.
5. tRNA is released after amino acid joined to polypeptide
6. Ribosome moves along the mRNA to form the polypeptide.

When the end of the sequence is reached, the newly formed polypeptide chain is released from the ribosome and folded and a protein forms

Question 26

What is required to make these peptide bonds ?

Answer 26

ATP

Question 27

What is the proteome of a cell ?

Answer 27

The proteome is the number of different proteins that a cell is able to produce / DNA is able to code for