4.1 DNA, Genes and Chromosomes

Question 1

compare DNA in eukaryotic cells with DNA in prokaryotic cells (similarities)

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

contrast DNA in eukaryotic cells with DNA in prokaryotic cells (differences)

Answer 2

-eukaryotic DNA is longer
-eukaryotic DNA is linear, prokaryotic DNA is circular
-eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
-eukaryotic DNA contain introns, prokaryotic DNA does not

Question 3

what is a chromosome?

Answer 3

-long, linear DNA + its associated histone proteins
-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 (eg. ribosomal RNA or tRNA)

Question 5

what is a locus?

Answer 5

-fixed position a gene occupies on a particular DNA molecule

Question 6

describe the nature of the genetic code

Answer 6

-triplet code
-universal
-non-overlapping
-degenerate

Question 7

how is the genetic code a triplet code

Answer 7

-a sequence of 3 DNA bases, called a triplet, codes for a specific amino acid

Question 8

how is the genetic code universal

Answer 8

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

Question 9

how is the genetic code non-overlapping

Answer 9

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

Question 10

how is the genetic code degenerate

Answer 10

-an amino acid can be coded for by more than one base triplet

Question 11

what are ‘non-coding base sequences’ and where are they found?

Answer 11

-non-coding base sequence - DNA that does not code for amino acid sequences / polypeptides:
1. between genes - eg. non-coding multiple repeats
2. within genes - introns

Question 12

describe non coding DNA in eukaryotes

Answer 12

-in eukaryotes, much of the nuclear DNA does not code for polypeptides

Question 13

what are introns?

Answer 13

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

Question 14

what are exons?

Answer 14

-base sequence of a gene coding for amino acid sequences (in a polypeptide)