DNA, genes and protein synthesis

what is a major difference in the DNA found in eukaryotes and prokaryotes

dna in prokaryotes is not associated with any proteins - eukaryotic dna associates with histone proteins

what are the main proteins associated with dna

histones (globular)

what is the role of histones

to organise and condense the dna so it fits tightly in the nucleus

histone

proteins that - with dna - form chromosomes in the nuclei of eukaryotic cells

what do nucleotides join together by and how are the bonds formed

joined together by phosphodiester bonds formed in condensation reactions

thymine, uracil and cytosine are all what

pyrimidines

adenine and guanine have double ring structures and are classified as

purine bases

chromatin

tightly coiled combination of DNA and proteins - what chromatids are made of

dna coiled around histone proteins makes what

chromatin

the two chromatids that make up the double structure of a chromosome are known as what

sister chromatids

narrow region that joins together the two identical chromatids (strands of dna)

centromere

ends of the chromatids in chromosomes are sealed with protective structures called

telomeres

gene

a length of dna on a chromosome that codes for the production of one or more polypeptide chains and functional RNA

difference in structure of RNA and DNA

dna - double helix made of two polynucleotides joined by hydrogen bonds

rna- a singular short, polynucleotide chain

the genetic code is : (3 points)

1. degenerate
2. universal
3. non-overlapping

the three RNA molecules required for protein synthesis

mRNA, tRNA and rRNA

what depends on the sequence of amino acids in the protein molecule ( initial sequence is known as the primary structure of the protein molecule)

the shape and behaviour

what do the genes in DNA molecules control and how

protein structure and function - they determine the exact sequence in which amino acids join together when proteins are synthesised

codon

sequence of three bases on mRNA that codes for a specific amino acid

triplet

sequence of three bases that codes for an amino acid

locus

position of a gene on a chromosome

non-coding sections of dna

introns

coding regions of dna

exons

how many amino acids

20

how many possible triplets are there

64

what does ‘non-overlapping’ mean

each triplet is only read once and triplets don’t share any bases

what are genes separated by

non-coding repeats of bases

alleles

different forms of the same gene

the genetic code is degenerate meaning what

more than one triplet can code for an amino acid

what does the genetic code being degenerate reduce

the number of mutations - mistakes in base sequence

3 types of mutations

1. base deletion
2. insertion
3. substitution

two examples of harmful mutations that cause illness

1. cystic fibrosis - production of sticky mucus
2. sickle cell anaemia - mutated haemoglobin distorts rbc shape

the genetic code is universal meaning what

almost every organism uses the same code - the same codons code for the same amino acids in all living things

non-coding dna in genes are known as

introns

the 2 stages of protein synthesis

transcription and translation

messenger RNA function

type of RNA that carries genetic info from nucleus to ribosome for translation

when is mRNA created

during transcription

transfer RNA function

form of RNA that carries specific amino acids to the ribosomes

tRNA structure

single stranded, clover leaf shape, one side longer than the other - opposite end has an anticodon specific to the amino acid

proteome

full range of proteins that a cell is able to produce

what base does RNA contain instead of thymine

uracil

3 stages of transcription

1. initiation
2. elongation
3. termination

genome

complete set of genes in a cell

transcription

first stage of protein synthesis - formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of DNA as a template

first 2 steps of transcription

1. DNA helicase breaks the hydrogen bonds between the complementary bases - dna uncoils and strands are separated
2. one of the DNA strands is used as a template

the dna strand used as a template is known as what

the antisense strand

the 3rd and 4th steps of transcription

3. free RNA nucleotides align by complementary base pairing and join by phosphodiester bonds - forming the pre -mRNA molecule (uracil instead of thymine)
4. enzyme RNA polymerase joins nucleotides by phosphodiester bonds, when a stop codon is reached process stops

roughly how many dna bases are exposed at a time during transcription

12

5th step of transcription (in eukaryotes)

pre-mRNA is spliced to remove introns - functional exons are joined together to make mRNA which then leaves nucleus through pore and attaches to ribosome

what happens during translation

amino acids join together to form a polypeptide chain

first 2 steps of translation

1. mRNA attaches to ribosome at starting codon and tRNA collects amino acid
2. tRNA anticodon binds to mRNA codon by complementary base pairing - two at a time - tRNA brings specific amino acid

3rd and 4th steps of translation

3. amino acids attached to the 2 tRNA molecules join by peptide bond with use of ATP - the first tRNA then detaches from the amino acid and is released
4. ribosome moves along the mRNA to form the polypeptide

with what do the amino acids join together and form a peptide bond

ATP - hydrolysed to provide energy

what amino acid does the first tRNA always carry

methionine

what does the first tRNA molecule form with the start codon

hydrogen bond

in what sort of direction does the ribosome move along the mRNA

5’ to 3’ direction

where does translation occur

in the cytoplasm

3 differences in mRNA and tRNA structure (not to do with shape)

1. mRNA doesn’t have hydrogen bonds, tRNA does
2. mRNA doesnt have amino acid binding site
3. mRNA has more nucleotides or is longer
4. mRNA has codons, tRNA has an anticodon