4.1 DNA, genes and chromosomes Flashcards
Describe prokaryotic DNA.
CIRCULAR DNA:
- singular, circular chromosomal DNA
- not associated with histones
- double-stranded
- suspended in the cytoplasm
PLASMIDS:
- also may have one or more plasmids → genes for antibiotic-resistance often found in plasmids, only contains a few genes
Describe eukaryotic DNA.
- found in the nucleus
- associated with histones and other enzymes used in copying and repairing the DNA
- one very long, condensed DNA molecule
- tightly coiled combination of DNA and proteins is called chromatin – this is what chromatids, and therefore chromosomes, are made of
Is mitochondrial and chloroplast DNA similar to that of prokaryotes or eukaryotes?
Prokaryotes → endosymbiosis
What is a gene?
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule.
Describe how a gene is a code for the production of a polypeptide.
The base sequence in the triplet code determines the shape and behaviour of a protein molecule (the protein’s primary structure).
What are the functional RNA molecules?
The RNA molecules that are required for protein synthesis
mRNA - the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains
tRNA - amino acids are carried to the ribosome by transfer RNA molecules
rRNA - ribosomal RNA molecules form part of the structure of ribosomes
What is a locus?
The fixed position occupied by a gene on a DNA molecule.
What is an allele?
Different forms of the same gene.
- they have different nucleotide sequences
- but they still occupy the same locus on the chromosome
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes
What is a triplet code?
A sequence of three bases that codes for one amino acid.
3 features of the genetic code.
- Start codons and stop codons send signals that tell the cell where individual genes start and stop so it reads the DNA correctly (i.e. each base is only read once) → code is non-overlapping
- There are 64 different triplet codes but only 20 amino acids so multiple codons code for the same amino acid → code is degenerate
- Most organisms use the same genetic code → code is universal
What is an intron.
Non-coding DNA so does not code for any amino acids.
What is an exon.
DNA that codes for amino acids.
Where are non-coding multiple repeats found?
Between genes (positioned at the telomeres).
Where are introns found?
Within gene (between exons).
