3.4.1 - DNA, genes and chromosomes

Question 1

how would you describe DNA molecules in prokaryotic cells?

Answer 1

short, circular, not associated with proteins

Question 2

how would you describe DNA molecules in eukaryotic cells?

Answer 2

found in nucleus, long, linear, associated with proteins (histones)

Question 3

what is a chromosome formed from?

Answer 3

a DNA molecule and its associated proteins

Question 4

where else in eukaryotic cells is DNA found other than the nucleus?

Answer 4

mitochondria and chloroplasts

Question 5

what makes the DNA in the mitochondria and chloroplasts different from the DNA in the nucleus?

Answer 5

it is more similar to the DNA of prokaryotes than eukaryotes - short, circular, not associated with proteins

Question 6

what is a gene?

Answer 6

a base sequence of DNA which code for:
1. the amino acid sequence of a polypeptide
2. a functional RNA (including ribosomal RNAs and tRNAs)

Question 7

what is a locus?

Answer 7

the fixed position occupied by a gene on a particular DNA molecule

Question 8

what is a triplet?

Answer 8

a sequence of three DNA bases which codes for a specific amino acid

Question 9

how can you describe the genetic code and what does this mean?

Answer 9

universal - applies to all living organisms
non-overlapping - read in triplets 3 bases at a time, so there is no overlap between triplet codes
degenerate - each amino acid may be coded for by more than one triplet code (codon)

Question 10

what is the nature of the nuclear DNA in eukaryotes?

Answer 10

much of it doesn’t code for polypeptides - there are non-coding multiple repeats of base sequences between genes

Question 11

what are exons?

Answer 11

sequences within genes which do code for amino acid sequences

Question 12

what are introns?

Answer 12

non-coding sequences of genes which separate exons