Topic 4

Question 1

What is the difference between Eukaryotic and Prokaryotic DNA?

Answer 1

• E is linear, P is circular
• E is longer, P is shorter
• E coils by histone proteins, P supercoils
• E is found in the nucleus, P is found in the cytoplasm
• E contains introns, P does not

Question 2

How does DNA condense into chromosomes?

Answer 2

• DNA wraps around histone proteins
• this forms the DNA-histone complex
• this then coils further to form a chromosome

Question 3

Other than the nucleus, what organelles contain DNA? Does this DNA have eukaryotic or prokaryotic properties?

Answer 3

Mitochondria and chloroplasts. Prokaryotic properties, circular, short, does not associate with histones et.c.

Question 4

Define gene

Answer 4

Short section of DNA that codes for a polypeptide or functional RNA.

Question 5

What is the difference between introns and exons?

Answer 5

Introns are non-coding regions of a DNA sequence that do not code for amino acids. Whereas exons are coding regions that do code for amino acids.

Question 6

Define locus

Answer 6

A locus is a specific position on a chromosome where a gene is located.

Question 7

Define genome

Answer 7

Complete set of genes within a cell.

Question 8

Define proteome

Answer 8

Full range of proteins a cell is capable of producing.

Question 9

Define genetic code

Answer 9

Sequence of bases that code for amino acids.

Question 10

Define triplet

Answer 10

3 DNA bases that code for an amino acid.

Question 11

Define universal (in terms of the genetic code)

Answer 11

Each triplet codes for the same amino acid in all organisms.

Question 12

Define non-overlapping (in terms of the genetic code)

Answer 12

Each base in the DNA sequence is only read once.

Question 13

Define degenerate (in terms of the genetic code)

Answer 13

Most amino acids are coded for by more than one triplet.

Question 14

What are non-coding repeats?

Answer 14

Sections of a DNA sequence with repeating bases (ATTATTATT et.c.) that do not code for amino acids.

Question 15

Define allele

Answer 15

Different forms of the same gene.

Question 16

When are alleles found at the same locus on each chromosome in a homologous pair?

Answer 16

When they code for the same characteristic e.g. eye colour

Question 17

What does mRNA stand for?

Answer 17

Messenger ribonucleic acid

Question 18

What process synthesises mRNA molecules?

Answer 18

Transcription

Question 19

What is the role of mRNA?

Answer 19

Caries genetic information from DNA to ribosomes for protein synthesis.

Question 20

Describe the structure of mRNA

Answer 20

Single-stranded and linear.

Question 21

Define codon

Answer 21

Sequence of 3 bases on mRNA that code for an amino acid.

Question 22

What does tRNA stand for?

Answer 22

Transfer ribonucleic acid

Question 23

What is the role of tRNA?

Answer 23

Transports amino acids to the ribosome to build up a polypeptide chain.

Question 24

What is the structure of tRNA?

Answer 24

Single-stranded, hydrogen bonds, anticodon, clover-leaf shape, amino acid binding site.

Question 25

Define anticodon

Answer 25

Sequence of 3 bases at one end of a tRNA molecule.

Question 26

What are the similarities of mRNA and tRNA?

Answer 26

- single-stranded - both contain ribose, phosphate and a nitrogenous base

Question 27

What are the differences between mRNA and tRNA?

Answer 27

- mRNA has codons, is longer, is linear, does not have hydrogen bonds, and does not have an amino acid binding site - tRNA has anticodons, is shorter, is clover-leaf shaped, has hydrogen bonds, and has an amino acid binding site.

Question 28

What is transcription?

Answer 28

The process of copying the genetic code from DNA onto an mRNA molecule.

Question 29

Why are hydrogen bonds broken during transcription?

Answer 29

H-bonds need to break down so the double helix can unwind and the DNA can be separated.

Question 30

What is the role of RNA polymerase?

Answer 30

RNA polymerase forms phosphodiester bonds between RNA nucleotides to form an mRNA molecule.

Question 31

What happens when RNA polymerase reaches the stop signal?

Answer 31

It stops making RNA and detaches from DNA.

Question 32

Where does transcription take place?

Answer 32

The nucleus.

Question 33

Define splicing

Answer 33

The process of removing introns from a pre-mRNA molecule.

Question 34

What happens to mRNA after transcription?

Answer 34

Leaves the nucleus for translation.

Question 35

Why does prokaryotic mRNA not undergo splicing?

Answer 35

Prokaryotic mRNA does not contain introns.

Question 36

What are the steps involved in transcription?

Answer 36

- hydrogen bonds are broken to unwind the double helix and separate the DNA strands (by DNA helicase which is attached to RNA polymerase) - free RNA nucleotides attract to their complementary bases on one DNA strand - RNA polymerase forms phosphodiester bonds between RNA nucleotides to make mRNA - when RNA polymerase reaches a stop signal, it stops making mRNA and detaches from the DNA - mRNA then leaves the nucleus and enters the cytoplasm (- these are the generic steps for eukaryotic and prokaryotic organisms, however in eukaryotic organisms splicing will also take place.)

Question 37

What is translation?

Answer 37

The process of using mRNA and tRNA to build a polypeptide chain.

Question 37

Where does a mRNA molecule initially bind to a ribosome?

Answer 37

The start codon (AUG).

Question 38

Where in the cell does translation take place?

Answer 38

Ribosomes.

Question 39

Which part of a tRNA molecule binds to a mRNA molecule?

Answer 39

The anticodon on tRNA binds to the codon on mRNA.

Question 40

How many tRNA molecules bind to a ribosome at a time?

Answer 40

Two.

Question 41

During translation, what happens when a ribosome reaches a stop codon?

Answer 41

The polypeptide chain detaches from the ribosome.

Question 42

Describe how amino acids are joined together in the process of translation?

Answer 42

Amino acids are joined by using ATP to form a peptide bond between them.

Question 43

What are the steps involved in translation?

Answer 43

1) mRNA binds to a ribosome at the start codon. 2) A tRNA with a complementary anticodon binds to the first mRNA codon. 3) A second tRNA with a complementary anticodon binds to the next mRNA codon. 4) ATP is used to form a peptide bond between the two amino acids on the tRNA molecules. 5) The first tRNA molecule is released, leaving its amino acid behind. 6) The ribosome moves along the mRNA, building up an amino acid chain. 7) When the ribosome reaches a stop codon on mRNA, the polypeptide chain detaches from it.