Biology - DNA , GENES AND PROTEIN SYNTHESIS

How does the genetic code provide evidence for evolution?

it is the same in nearly every living organisim

List 3 differences between eukaryotic DNA and prokaryotic DNA

eukaryotic: long, linear and associated with histones

prokaryotic: short , circular and naked (no histones)

What is a chromosome?

one molecule of DNA, with both polynucleotide strands twisted together to form a double helix wrapped around histone proteins

Define genome

the complete set of genes in a cell

Define proteome

the complete set of proteins a cell is able to produce

what is a codon?

sequence of 3 adjacent nucleotides in mRNA/DNA that codes for 1 amino acid

what is the genetic code?

a series of bases, arranged in triplets, that code for a sequence of amino acids.

it is universal, degenerate and non overlapping

why is the genetic code described as degenerate ?

most amino acids are coded for by more than 1 triplet

why is the genetic code non-overlapping?

each base in the sequence is only read once

why is the genetic code universal?

all living organisms use the same codons to specify the same amino acids

what are introns?

non coding sections of a gene

what are exons?

coding sections of a gene that code for amino acids

what are the 2 steps of protein synthesis (in correct order) ?

transcription followed by translation

what happens during transcription? (summary)

a DNA template is copied to make sections of pre-mRNA which are spliced (introns removed and exons joined together) to make a functional mRNA containing only exons

where does transcription occur?

nucleus

how does the mRNA move from the nucleus to the cytoplasm?

through the nuclear pores

what is the role of the enzyme DNA helicase in transcription?

breaks the H bonds between complementary base pairs in DNA to unwind the DNA and expose the bases

what is the role of the enzyme RNA polymerase in transcription?

it matches up free RNA nucleotides to complementary bases on the unzipped DNA, and joins the RNA nucleotides to form pre-mRNA

what is a gene?

a section of DNA that contains information for making polypeptides and functional RNA

Define locus

the specific , fixed position of a gene or allele on a chromosome

are introns present in eukaryotic and prokaryotic cells?

no only eukaryotic

what is a chromatid ?

one of 2 identical, attached copies of a duplicated chromosome (2 threads- chromatids- make up a chromosome)

what are homologous chromosomes?

pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features

what is an allele?

one of a number of alternative forms of a gene found at the same location on the chromosome

RNA (ribonucleic acid) structure

single strand, each nucleotide made of: ribose (pentose sugar), base A,G,C or U and a phosphate group

what are the 2 types of RNA that are important in protein synthesis?

messenger RNA (mRNA)

transfer RNA (tRNA)

similarities of mRNA and tRNA

single polynucleotide chain

ribose (pentose sugar)

bases A,U,G,C

differences between mRNA and tRNA

mRNA longer chain than tRNA

mRNA single stranded helix; tRNA clover leaf shaped

mRNA chemically unstable (only present when required for protein synthesis); tRNA chemically stable

what is transcription?

production of mRNA using DNA

what is translation?

production of polypeptides from the sequence of codons carried by mRNA

describe the steps in transcription

• DNA helicase breaks H bonds between bases, causing DNA to unzip , exposing bases

• RNA polymerase moves along DNA template strand and attaches free nucleotides to their complementary bases on the DNA (T replaced by U in mRNA)

• RNA polymerase makes short strands of pre-mRNA until it comes to a terminator sequence

• sections of pre-mRNA spliced together to remove introns and join exon sequences forming mRNA

describe the steps in translation

• mRNA moves from nucleus through a nuclear pore to cytoplasm and start codon (AUG) attaches to a ribosome

• a tRNA (carrying specific AA, methionine) with a complementary anticodon (UAC) moves to ribosome and pairs with first mRNA codon

• ribosome moves along mRNA to next codon and pairs with complementary tRNA to bring 2 AA carrying tRNAs together

• energy released from ATP used to form a peptide bond between the AA’s

• ribosome moves to 3rd mRNA codon , releasing 1st tRNA and pairing with a third

• when ribosome reaches a stop codon the polypeptide is complete and mRNA and tRNA’s released from ribosome