a gene is a section of dna that contains the coded information for making polypeptides or functional RNA
the gene locus is the particular position on the dna molecule where a particular gene is located
specific sequence of bases along the DNA polypeptide determines the primary structure of the protein
The order of bases on DNA is called the genetic code which consists of triplets of bases, with each triplet of bases coding for a particular amino acids known as a codon#
the non-coding sections of DNA are called introns and the coding regions are called exons.
an allele is a different form of the same gene
chromosomes are tightly coiled up DNA within the nucleus (eukaryotic)
structural differences in the DNA found in eukaryotes and prokaryotes:
Eukaryotic DNA is linear, prokaryotic DNA is circular
Eukaryotic DNA is associated with histone proteins (dna wound tightly to fit in nucleus as chromosome), prokaryotic DNA is not associated with histones
Eukaryotic DNA is longer than prokaryotic DNA
mitochondrial DNA and chloroplast DNA are similar to prokaryotic dna:
short
circular
not associated with histones (no chromosomes)
start codon are 3 bases at the start of every gene which initiates translation (coding)
stop codon are 3 bases at the end of every gene to mark the end of a polypeptide causing translation to stop and ribosome to detach
Features of the genetic code:
Tripletcode = 3 bases code for an amino acid [4 bases + 20 amino acids ----> 4^3 = 64 enough to satisfy 20]
Degenerate = most amino acids are coded for by more than one triplet
Non-overlapping = codons do not overlap so each base in the sequence is read only once
Almostuniversal = each triplet codes for the same amino acid in all organisms
being degenerate is an advantage as if it mutates some mutations will have no effect on the organism since the same protein will still be produced
being universal is indirect evidence for evolution and makes genetic engineering possible
a genome is an organisms complete set of dna in a cell
a proteome is the full range of proteins that a cell is able to produce - depending on which proteins are currently needed
sections of the DNA (genes) molecules which code for polypeptides are transcribed onto a single stranded messenger RNA and leave to ribosome out of nuclear pores
in dna 3 bases are known as triplets while in mRNA three bases are known as codons
complete proteome is the full range of proteins produced by the genome
structure of RNA includes a single strand made up of a nucleotide:
pentose sugar ribose
one nitrogenous base (A, G, C, U)
a phosphate group
mRNA:
polynucleotide chain arranged in a single helix
Produces during transcription carries the genetic code from the nucleus to the cytoplasm (has instructions for making a protein on the ribosome in translation)
carry info in the form of codons
tRNA:
relatively small and single stranded
folded into a clover leaf shape
Contains an amino acid binding site at one end and an anticodon at the opposite end (bind to complementary codons on mRNA to sequence into a protein’s primary sequence)
Carries amino acids to the ribosome during translation
transcription is the process of making (pre) mRNA using part of DNA as a template
Transcription:
The enzyme dna helicase breaks the hydrogen bonds between bases for dna helix to unzip exposing bases to act as a template (only one chain)
Free mRNA nucleotides in nucleus align opposite to exposed complementary dna bases RNA polymerase to move along strand joining nucleotides together forming phosphodiester bond
when RNA polymerase reaches stop triplet code it detaches forming pre-mRNA molecule
SPLICING = pre-mRNA has to be modified to become mRNA so introns (non-coding bases) are spliced out (exons are spliced together) forming mRNA
In prokaryotes, transcription results directly in the production of mRNA from DNA
In eukaryotes, transcription results in the production of pre-mRNA; this is then spliced to form mRNA.
Translation is the production of of polypeptides from the sequence of codons carried by the mRNA
Translation:
mRNA leaves the nucleus attaching to start codon at ribosome
The tRNA molecule with the complementary anticodon pairs up with the codon on the mRNA (carrying a specific amino acid)
the ribosome moves along the mRNA so other complementary tRNA anticodon can attach to next codon (tRNA carries another amino acid)
the amino acids (delivered by the tRNA) are joined by a peptide bond [requires an enzyme + ATP for energy]
once tRNA releases amino acid it leaves - continuing as ribosome moves across until ribosome reaches stop codon at end and ribosome detaches - TRANSLATION ENDS