4.1 - DNA, genes and chromosomes Flashcards
Describe the DNA molecules present in prokaryotic cells
- short
- circular
- not associated with histones/protein
Describe the DNA molecules present in eukaryotic cells
- in nucleus
- long
- linear
- associated with histones (proteins)
What is a chromosome made up of?
DNA molecule and its associated proteins
Describe the DNA found in chloroplasts and mitochondria
- short
- circular
- not associated with histones/protein
What is a gene?
DNA base sequence that codes for the amino acid sequence of a polypeptide and a functional RNA e.g rRNA or tRNA
What is a locus?
fixed position a gene occupies on a particular DNA molecule
Define triplet
sequence of 3 DNA bases which codes for a specific amino acid
Describe the 3 key features of the genetic code
- universal: same bases in all living organisms
- non-overlapping: each triplet is only read once
- degenerate: more than 1 triplet codes for the same amino acid, which means there are less mutations which alter the amino acid sequence
What is an intron?
DNA that does not code for a polypeptide, positioned between genes
What is an exon?
base sequence coding for a polypeptide
What types of molecule are DNA and RNA?
polymers (of nucleotides)
How many hydrogen bonds between base pairs?
A+T/U: 2
C+G: 3
Describe how a phosphodiester bond is formed between 2 nucleotides within a DNA molecule
- condensation reaction
- between phosphate and deoxyribose
- catalysed by DNA polymerase
Describe how a gene is a code for the production of a polypeptide
- base sequence
- in triplet
- determines amino acid sequence
Additional 3 differences between DNA in the nucleus
of a plant cell and DNA in a prokaryotic cell
Prokaryotes:
- fewER genes
- not associated with histones unlike nuclear DNA
- no introns, nuclear DNA has intons
(make sure to say -ER when comparing!)
