3.4.1 DNA, genes + chromosomes

Describe DNA molecules in prokaryote cells

Short, circular + not associated with proteins → don’t form chromosomes

Describe DNA molecules in eukaryote cells

Very long, linear + associated with proteins called histones → together a DNA molecule + its associated proteins form a chromosome

What organelles in eukaryotic cells also contain DNA other than the nucleus + describe their DNA structure

Mitochondria + chloroplasts

• short, circular, not associated with protein + doesn’t contain introns → like prokaryotic DNA

During cell division in eukaryotes, DNA + histones are organised into what?

structures → chromosomes

What is a gene?

A sequence of DNA bases that codes for a specific amino acid sequence of a polypeptide

Why do diploid cells have chromosomes in pairs?

One was inherited from one parent + one from the other

What is a locus?

A fixed position of a gene

A homologous pair of chromosomes carries the same ____ in the same loci but not necessarily the same ___

genes

alleles

What are alleles?

The different forms a gene can exist in

A homologous pair of chromosomes consists of a ____ + ____ chromosome

maternal + paternal

What is a base triplet?

A sequence of three nucleotide bases that codes for a specific amino acid → there are mRNA + DNA base triplets

mRNA base triplets are specifically referred to as…

codons

The presence of 4 different nucleotides in DNA + RNA results in how many different DNA triplets / mRNA codons being produced?

64 → to code for the 20 commonly occurring amino acids in living organisms

How does 64 base triplets result in only 20 amino acids being coded for?

The triplet code is degenerate with different triplets / codons coding for the same amino acid

What are stop codes?

Triplet codes that don’t code for an amino acid but indicate the end of the code for a specific polypeptide

What’s so important of the DNA triplet code ATG?

It’s the start code for all the sequences coding for a polypeptide

What two things is the triplet code?

• Non-overlapping → each base is only read once as part of a specific triplet

• Universal → same triplets code for the same amino acids in all organisms

In eukaryotes, a lot of the DNA doesn’t code for polypeptides → which DNA is this?

Introns → base sequences present within genes but don’t code for amino acids

Multiple repeats → some of the base sequences present between genes - often consists of the same base sequence occurring again + again

What are exons?

Base sequences in genes that do code for amino acids

What is the genome?

The complete set of genes (+ the non-coding DNA) in a cell

What is the proteome?

Full range of proteins that a cell is able to produce

Protein synthesis can be divided into two main processes - what are they?

Transcription + translation