3.4.1 DNA , Genes and chromosomes ( 3.4 Genetic information , variation and relatoonships between organisms)

Question 1

What are the similarities between DNA in eukaryotic and prokaryotic cells?

Answer 1

Nucleotide structure is identical - deoxyribose attached to phosphate and a base. Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds. DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes.

Short, circular, not associated with proteins.

Question 2

What are the differences between DNA in eukaryotic and prokaryotic cells?

Answer 2

Eukaryotic DNA is longer, linear, and associated with histone proteins. Prokaryotic DNA is circular and not associated with proteins. Eukaryotic DNA contains introns, while prokaryotic DNA does not.

Question 3

What is a chromosome?

Answer 3

Long, linear DNA + its associated histone proteins, located in the nucleus of eukaryotic cells.

Question 4

What is a gene?

Answer 4

A sequence of DNA (nucleotide) bases that codes for:
• the amino acid sequence of a polypeptide
• or a functional RNA (e.g., ribosomal RNA or tRNA).

Question 5

What is a locus?

Answer 5

Fixed position a gene occupies on a particular DNA molecule.

Question 6

What is the nature of the genetic code?

Answer 6

Triplet code: A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid.
Universal: The same base triplets code for the same amino acids in all organisms.
Non-overlapping: Each base is part of only one triplet, so each triplet is read as a discrete unit.
Degenerate: An amino acid can be coded for by more than one base triplet.

Question 7

What are non-coding base sequences?

Answer 7

DNA that does not code for amino acid sequences or polypeptides.

Question 8

Where are non-coding base sequences found?

Answer 8

1. Between genes (e.g., non-coding multiple repeats)
2. Within genes (introns)

In eukaryotes, much of the nuclear DNA does not code for polypeptides.

Question 9

What is an exon?

Answer 9

Base sequence of a gene coding for amino acid sequences in a polypeptide.

Question 10

What is an intron?

Answer 10

Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells.

Question 11

Describe how a gene is a code for the production of a polypeptide

Answer 11

• base sequence is in triplets
• determine the order of amino acid sequences in a polypeptide