Chapter 8 DNA and Protein synthesis

Question 1

What is a gene?

Answer 1

Section of DNA that contains a code for making a polypeptide and functional RNA. The code is a specific sequence of bases.

Question 2

What is a locus?

Answer 2

Location of a particular gene on a chromosome is called the locus.

Question 3

What is an allele?

Answer 3

One of a number of alternative forms of a gene.

Question 4

What is a chromosome?

Answer 4

In a eukaryotic cell nucleus, DNA is stored as chromosomes.

Question 5

What is a homologous pair?

Answer 5

They are a pair of chromosomes with exactly the same size, and have exactly the same genes but might have different alleles.

Question 6

What is a histone?

Answer 6

The protein that DNA is wrapped around.

Question 7

Describe DNA in prokaryotic cells.

Answer 7

DNA is in chromosomes.
DNA molecules are shorter and circular.
DNA is not wound around histones.
It supercoils to fit into cell.

Question 8

What is the DNA in mitochondria and chloroplasts like?

Answer 8

It is short and circular and also not wrapped around histones.

Question 9

How is the genetic code degenerate?

Answer 9

Each amino acid is coded for by more than one triplet of bases.

Question 10

How is the genetic code universal?

Answer 10

The same triplet of bases code for the same amino acid in all organisms.

Question 11

How is the genetic code non-overlapping?

Answer 11

Each base in a gene is only part of one triplet of bases that codes for one amino acid. Therefore each codon is read as a discrete unit.

Question 12

What are introns?

Answer 12

Sections of DNA that do not code for amino acids and therefore polypeptide chains. Introns are only found in eukaryotic DNA.

Question 13

What are Exons?

Answer 13

Sections of DNA which do code for amino acids.

Question 14

What is the genome and the proteome?

Answer 14

An organisms complete set of DNA in one cell and the proteome is the full range of proteins in one cell.

Question 15

What is RNA?

Answer 15

A polymer of a nucleotide formed of ribose, a nitrogenous base and a phosphate group

Question 16

What bases does RNA contain?

Answer 16

Adenine, guanine, cytosine and uracil.

Question 17

What is the function of RNA?

Answer 17

It is to copy and transfer the genetic code from DNA in the nucleus to the ribosomes.

Question 18

What is mRNA?

Answer 18

A copy of a gene from DNA.

Question 19

Why is mRNA short lived?

Answer 19

As it is only needed temporarily to create a protein.

Question 20

Describe the structure of mRNA.

Answer 20

It is single stranded and every 3 bases in the sequence code for a specific amino acid. These 3 bases are called codons.

Question 21

What is the structure of tRNA?

Answer 21

Single stranded but folded to create a cloverleaf shape. This shape is held together by hydrogen bonds.

Question 22

What is the function of tRNA?

Answer 22

To attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create the polypeptide chain.

Question 23

What is the anticodon in tRNA?

Answer 23

Specific amino acids attach to specific tRNA molecules and this is determined by three bases found on the tRNA which are complementary to three bases on mRNA. These are called the anticodon.

Question 24

Describe the process of transcription.

Answer 24

• DNA helix unwinds to expose the bases as a template.
• Only one chain of DNA acts as template.
• Unwinding and zipping is catalysed by DNA helicase.
• DNA helicase breaks hydrogen bonds between the bases.
• Free mRNA nucleotides in nucleus align opposite exposed complimentary DNA bases.
• Enzyme RNA polymerase bonds together the RNA nucleotides to create phosphodiester bonds.

Question 25

What happens in splicing?

Answer 25

The introns are spliced out by a protein called a splicesome. This leaves behind just exons.

Question 26

Describe how translation works.

Answer 26

- Once modified mRNA has left nucleus it attaches to to ribosome in cytoplasm. - Ribosome attaches to start codon. - The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held in place by the ribosome. - Ribosome will move along the mRNA molecule to enable another complimentary tRNA to attach to the next codon on the mRNA. - The 2 amino acids that have been delivered by the tRNA molecules are joined by a peptide bond. This is catalysed by an enzyme and requires ATP. - This continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The ribosome detaches and translation ends. Polypeptide chain is now created and will enter golgi body for folding and modification.

Question 27

Describe how independent segregation occurs

Answer 27

-Homologous pairs of chromosomes line up opposite each other at equator of cell. -It is random which side of equator paternal and maternal chromosomes from each homologous pair lie. -These pairs are separated, so one of each homologous pair ends up in daughter cell.

Question 28

Describe how crossing over works

Answer 28

When homologous pairs line up opposite each other at the equator, parts of the chromatids can become twisted around each other. -This puts tension on the chromatids, causing pairs of chromatid to break. -The broken parts of chromatid recombines with another chromatid.

Question 29

What is non-disjunction?

Answer 29

When the chromosomes or chromatids do not spit equally during anaphase.

Question 30

What is polyploidy?

Answer 30

Changes in whole sets of chromosomes.

Question 31

What is aneuploidy?

Answer 31

Changes in number of individual chromosomes.

Question 32

What is genetic diversity?

Answer 32

The number of different alleles in a population.

Question 33

What is evolution?

Answer 33

The change in allele frequency over many generations in a population.

Question 34

Describe the process of natural selection.

Answer 34

-New alleles for a gene is caused by random mutations. -If new alleles increases the chances of individual to survive in that environment, then they are more likely to survive and reproduce. -This reproduction passes on the advantageous allele to next generation. -As a result over many generations, the new allele increases in frequency in population.

Question 35

What is directional selection?

Answer 35

When one of the extreme traits has the selective advantage. Occurs when there is a change in environment.

Question 36

What is stabilising selection?