4.1 DNA, genes and chromosomes

Question 1

How is DNA structured?

Answer 1

• Polynucleotide (each nucleotide formed from deoxyribose, a phosphate group and nitrogen-containing organic base)
• Double stranded/helix
• Phosphodiester bonds join adjacent nucleotides
• Hydrogen bonds between complementary base pairs

Question 2

Eukaryotic DNA

Answer 2

Longer
Linear
Associated with histone proteins
Introns present

Question 3

Prokaryotic DNA

Answer 3

Shorter
Circular
Not associated with histone proteins
No introns

Question 4

What is a gene?

Answer 4

• A sequence of DNA bases that codes for the amino acid sequence of a polypeptide
• Or functional RNA

Question 5

What is a locus?

Answer 5

Fixed position a gene occupies on a particular DNA molecule

Question 6

What is a chromosome?

Answer 6

• Long linear DNA and it’s associated histone proteins
• In the nucleus of eukaryotic cells

Question 7

Universal

Answer 7

The same base triplets code for the same amino acids in all organisms

Question 8

Non-overlapping

Answer 8

Each base is part of only one triplet so each triplet is read as a discrete unit

Question 9

Degenerate

Answer 9

An amino acid can be coded for by more than one triplet

Question 10

What are non-coding base sequences?

Answer 10

• DNA that doesn’t code for amino acids
• Positioned between genes (eg. Non-coding multiple repeats)
• Or within genes (eg. Introns)

Question 11

What are exons?

Answer 11

Base sequences of a gene coding for amino acid sequences

Question 12

What are introns?

Answer 12

Base sequences of a gene that doesn’t code for amino acids (only in eukaryotes)