4.1 DNA, genes and chromosomes

Question 1

What are the three components of

nucleotides?

Answer 1

A pentose sugar, a phosphate group, an

organic base.

Question 2

Describe the structure of DNA

Answer 2

Made up of a deoxyribose sugar, a
phosphate group, and one of four
organic bases (A,C,G,T). It is
double-stranded, and hydrogen bonds
between the bases form a helix shape.

Question 3

Describe the role of DNA.

Answer 3

Carries genetic information, determines

our inherited characteristics.

Question 4

Describe the structure of RNA.

Answer 4

Made up of a ribose sugar, a phosphate
group, and one of four organic bases
(A,C,G,U). It is single stranded.

Question 5

Describe the role of RNA.

Answer 5

Transfers genetic information from DNA

to ribosomes for protein synthesis.

Question 6

Which bases are purine and which are

pyrimidine?

Answer 6

Purine (double ring) = adenine, guanine.
Pyrimidine (single ring) = cytosine,
thymine, uracil.

Question 7

How is DNA in eukaryotic cells different

from in prokaryotic cells?

Answer 7

● Eukaryotic cells= found in nucleus, long and
linear. Associated with histone proteins to form
chromosomes. Mitochondria and chloroplasts
contain prokaryotic-like DNA.
● Prokaryotic cells= short and circular. Not
associated with proteins.

Question 8

What is the genetic code?

Answer 8

The order of bases on DNA. Consists of
codons (triplets of bases that code for a
particular amino acid).

Question 9

Identify features of the genetic code.

Answer 9

● Non-overlapping= each triplet is only read once.
● Degenerate= more than one triplet codes for the
same amino acid (64 possible triplets for 20
amino acids).
● Universal= same bases and sequences used by
all species.

Question 10

What is a gene?

Answer 10

A sequence of bases on a DNA molecule
that codes for a specific sequence of
amino acids to make a polypeptide. Can
also code for functional RNA.

Question 11

What is a locus?

Answer 11

The fixed position on a DNA molecule

occupied by a gene.

Question 12

What is an allele?

Answer 12

Different versions of the same gene,
found at the same locus on a
chromosome.

Question 13

What are exons and introns?

Answer 13

Exons= regions of DNA that code for
amino acid sequences. Separated by
one or more introns.
Introns= regions of DNA that do not code
for anything.

Question 14

Where are introns found?

Answer 14

between exons

within genes