3.4.1 DNA, genes and chromosomes Flashcards
Define gene
- a section of DNA located on a fixed site called the Locus
- contains a specific sequence of bases for the formation of polypeptides and functional RNA (ribosomal and transfer)
What are the three main features of the genetic code?
- universal - the same in almost all organisms
- non-overlapping - each triplet is read only once
- degenerate - all but two amino acids have more than one DNA triplet (as there are more possible triplet combos than there are amino acids)
How many different triplets and amino acids are there?
64 triplets - there are 20 amino acids so some are coded for by more than one triplet
Define stop code
don’t code for any amino acid and mark the end of a chain
Define exon
a base sequence which codes for a polypeptide sequence of amino acids
Define intron
non-coding sequences (only found in eukaryotes)
- removed during transcription and exons are joined (splicing)
Define non-coding repeats
positioned outside of the gene and contain the same base sequence repeated multiple times
Describe the main differences between prokaryotic and eukaryotic DNA
Prokaryotic VS Eukaryotic
* in cytoplasm - in nucleus
* circular - linear
* not associated with proteins - associate with histone proteins to form chromosomes
* shorter - longer
* no introns - introns
Describe DNA structure in eukaryotic cells
- DNA is wound around histone proteins - these also support the DNA
- DNA-histone complex is coiled and coils fold to form loops
- loops pack to form a chomosome
Describe DNA structure in prokaryotic cells
DNA loops condenses via supercoiling
What is DNA like within chloroplasts and mitochondria?
similar to prokaryotic cells - short, circular and not associated with histone proteins
Define homologous pair
a chromosome pair, one maternal and one paternal , with the same gene loci
Define Allele
alternative forms of the same gene (one allele is gained from each parent)
- slightly different base sequences
- different amino acid sequence
- different polypeptide formed