DNA, RNA and Protein Synthesis - DNA, Genes and Chromosomes

Question 1

How is genetic information stored in eukaryotic cells?

Answer 1

In linear DNA molecules that exist as chromosomes.

These are found in the nucleus.

Question 2

What is the DNA molecule in eukaryotes wound around?

Answer 2

Proteins called histones.

Question 3

What are histones?

Answer 3

Proteins that help to support the DNA

Question 4

How does the DNA in mitochondria and chloroplasts compare to the DNA in eukaryotes?

Answer 4

In mitochondria and chloroplasts,

DNA is circular
and shorter,
and isn’t associated with histone proteins.

(Similar to prokaryotic cells)

Question 5

How is genetic information stored in prokaryotic cells in comparison to that of eukaryotic cells?

Answer 5

As chromosomes, but the DNA is shorter and circular than in eukaryotes.

The DNA isn’t wound to histones – it condenses to fit in the cell by supercoiling:

DNA double helix

• -> circular chromosome
• -> coiled chromosome
• -> supercoiled

Question 6

What is a gene?

Answer 6

A sequence of DNA bases that codes for either a polypeptide or functional RNA.

Question 7

How do genes correspond to amino acids produced?

Answer 7

The sequence of amino acids in a polypeptide forms the primary structure of a protein.

Different polypeptides have a different number and order of amino acids.

It is the order of bases in a gene that determines the order of amino acids in a particular polypeptide.

Each amino acid is coded for by a sequence of three bases in a gene called a triplet.

Question 8

What is functional RNA?

Answer 8

RNA molecules other than mRNA, which perform special tasks during protein synthesis.

E.g.

• tRNA
• rRNA, which forms part of ribosomes.

Question 9

If a gene doesn’t code for a polypeptide, what does it code for?

Answer 9

Functional RNA

E.g.

• tRNA
• rRNA, which forms part of ribosomes.

Question 10

What is a cell’s genome?

Answer 10

The complete set of genes in a cell.

Question 11

What is a cell’s proteome?

Answer 11

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

Question 12

What is an intron?

Answer 12

A section of eukaryotic DNA that doesn’t code for an amino acid.

Question 13

What is an exon?

Answer 13

A section of eukaryotic DNA that codes for an amino acid

Question 14

When are introns removed?

Answer 14

During protein synthesis

Question 15

Why are introns removed?

Answer 15

So that they don’t affect the amino acid order

Question 16

What else, other than introns, does not code for an amino acid?

Answer 16

Regions of multiple repeats –
these are DNA sequences that repeat over and over.

For example: CCTTCCTTCCTT

These are called non-coding repeats.

Question 17

Why do alleles code for slightly different versions of the same polypeptide?

Answer 17

Because the order of bases in each allele is slightly different.

Question 18

How many chromosomes do humans have in total?

Answer 18

46

Question 19

How many pairs of chromosomes do humans have?

Answer 19

23

Question 20

What is a homologous pair?

Answer 20

A pair of matching chromosomes.

Both chromosomes are the same size
and have the same genes,

although they could have different alleles.

Question 21

When will alleles be found at the same fixed position (locus) on each chromosome in a homologous pair?

Answer 21

When they’re coding for the same characteristic.