DNA, genes and protein synthesis Flashcards
What is a gene?
a gene is a section of DNA that contains the coded info for making polypeptides and functional RNA
- Polypeptides make up proteins and so genes determine the proteins of an organism. Enzymes are proteins
The gene is a base sequence of DNA that codes for:
- amino acid sequence of a polypeptide
-or a functional RNA including ribosomal RNA and transfer RNA
Genetic code
- degenerate code: most amino acids are coded for more than one triplet
- non overlapping: sequence is only read once
- universal: each triplet codes for the same amino acid in all organims
- Exons: only certain sequences code for amino acids
- Introns: within the gene these exons are separated by further non-coding sequences
Prokaryotic and Eukaryotic DNA
- in prokaryotic cells, in bacteria the DNA molecules are shorter and they form a circle and are not associated with protein molecules. Prokaryotic don’t obviously have chromosomes
- in Eukaryotic cells, the DNA is longer and form a line rather than a circle and occur in association with proteins called histones to form structures called chromosomes.
The mitochondria and chloroplasts of eukaryotic cells also contain DNA which is short and circular and not associated with proteins
Chromosomes structure
- they’re really visible when a cell is dividing for the rest of the time they’re dispersed throughout the nucleus
- Each thread is called a chromatid because DNA has already replicated to give two identical DNA molecules
- The DNA in chromosomes is held by histone
DNA and histones
- a helix is wound around histones to fix it in position
- This DNA histone complex is then coiled and is further coiled before being packed into the chromosome
Homologous chromosomes
-one of each pair is derived from the chromosomes provided by the mother and father and the total number is referred to the diploid. in humans this is 46
What is an allele
an allele is one of a number of alternatives forms a gene
- each allele has a different base sequence and different amino acid sequence and produces a different polypeptide
- any change base sequence of a gene produces a new allele of that gene (mutation) and results in a different sequence of amino acids being coded for, this different sequence results in production of different polypeptide
Transferring the coded info
- sections of the DNA code are transcribed onto single stranded RNA so the DNA can be translated into proteins
proteins are synthesised where?
mRNA (messenger RNA)
what’s a codon
three bases on a mRNA that codes for a single amino acid
Genome
the complete set of genes in a cell including those in mitochondria and chloroplasts
Proteome/ complete proteome
the full range of proteins produced by the genome,
DNA structure
DNA is composed of two nucleotide chains wound around each other
RNA structure
RNA is a polymer made up of repeating mononucleotide subunits.
Each nucleotide is made up of:
- a pentose sugar ribose
- organic bases, adenine, guanine, cytosine and uracil
- a phosphate group
two types of RNA in protein synthesis
- messenger RNA
- transfer RNA