3.4.2 - DNA and protein synthesis Flashcards
what is a genome
the complete set of genes in a cell is known as the cell’s genome
what is a proteome
the full range of proteins that the cell is able to produce is known as a proteome
what is protein synthesis
protein synthesis is the production of proteins (polypeptides) from the information contained within a cell’s DNA
what is protein synthesis also known as
polypeptide synthesis
what is the 1st stage of protein synthesis?
transcription
what is transcription briefly
where the DNA code is copied into a molecule called mRNA
what is the 2nd stage of protein synthesis
translation
what is translation briefly
where the mRNA joins with a ribosome and the code it carries is used to synthesise a protein
what is RNA
single polynucleotide strand containing uracil instead of thymine. uracil always pairs with adenine during protein synthesis
name 2 different types of RNA
mRNA - messenger RNA
tRNA - transfer RNA
where is mRNA made?
mRNA is made during transcription
what does mRNA do?
mRNA carries the genetic code from the DNA to the ribosomes, where it’s used to make a protein during translation
what is mRNA?
mRNA is a single polynucleotide strand
what are 3 adjacent bases called in mRNA?
in mRNA, groups of 3 adjacent bases are usually called codons (sometimes called triplets/base triplets)
what is tRNA involved in?
tRNA is involved in translation
what does tRNA do?
tRNA carries the amino acids that are used to make proteins to the ribosomes
what is tRNA?
tRNA is a single polynucleotide strand that’s folded into a clover shape
what holds tRNA in its shape
hydrogen bonds between specific base pairs hold the molecule in this shape
tRNA : anticodons
each tRNA molecule has a specific sequence of 3 bases at one end called an anticodon and has an amino acid binding site at the other end
where does transcription happen in eukaryotic cells?
in eukaryotic cells, transcription happens in the nucleus
where does transcription happen in prokaryotic cells?
in prokaryotic cells, transcription takes place in the cytoplasm
what happens first in transcription
RNA polymerase attaches to the DNA
transcription: RNA polymerase attaches to the DNA
step one
transcription starts when RNA polymerase (an enzyme) attaches to the DNA double helix at the beginning of a gene
transcription: RNA polymerase attaches to the DNA
step two
in eukaryotes, the hydrogen bonds between the 2 DNA strands in the gene are broken by a DNA helicase attached to the RNA polymerase. This separates the strands, and the DNA molecule uncoils at that point, exposing some of the bases. one of the strands is then used as a template to make an mRNA copy
what happens second in transcription
complementary mRNA is formed
transcription: complementary mRNA is formed
step one
the RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. the free bases are attracted to the exposed bases
transcription: complementary mRNA is formed
step two
specific complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand (except the base T is replaced by U in RNA)
transcription: complementary mRNA is formed
step three
once the RNA nucleotides have paired up with their specific bases on the DNA strand, they’re joined together by RNA polymerase, forming an mRNA strand
what happens 3rd in transcription
RNA polymerase moves down the DNA strand
transcription: RNA polymerase moves down the DNA strand
step one
the RNA polymerase moves along the DNA, assembling the mRNA strand.
transcription: RNA polymerase moves down the DNA strand
step two
the hydrogen bonds between the uncoiled strands of DNA reform once the RNA polymerase has passed by and the strands coil back into a double helix
what happens 4th in transcription?
RNA polymerase reaches stop signal
transcription: RNA polymerase reaches stop signal
step one
when RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA
transcription: RNA polymerase reaches stop signal
step two
in eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosomes in the cytoplasm where the next stage of protein synthesis takes place
editing mRNA
does transcription produce the same products in eukaryotes and prokaryotes?
transcription produces different products in eukaryotes and prokaryotes
editing mRNA
in eukaryotes what are copied into mRNA during transcription
in eukaryotes, the introns and exons are both copied into mRNA during transcription
editing mRNA
splicing
mRNA strands containing introns and exons are called pre-mRNA. Splicing then occurs = introns are removed and the exons joined together
editing mRNA
where does splicing take place
splicing takes place in the nucleus
editing mRNA
what happens after splicing
the mRNA leaves the nucleus for the next stage of protein synthesis (translation)
editing mRNA
how is mRNA produced in prokaryotes
in prokaryotes, mRNA is produced directly from the DNA without splicing taking place
editing mRNA
why doesn’t splicing occur in prokaryotes
there is no need for splicing as there is no introns in prokaryotic DNA
where does translation occur
in eukaryotes and prokaryotes, translation takes place at the ribosomes in the cytoplasm
what happens during translation
amino acids are joined together to make a polypeptide chain (proteins), following the sequence of codons carried by the mRNA
translation
step one
mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP gives the energy needed for the bond between the amino acid and the tRNA molecule to form
translation
step two
a tRNA molecule (carrying an amino acid), with an anticodon that’s complementary to the 1st codon on the mRNA, attaches itself to the mRNA by complementary base pairing. a 2nd tRNA molecule attaches itself to the next codon on the mRNA in the same way
translation
step three
the 2 amino acids attached to the tRNA molecules are joined by a peptide bond. the first tRNA molecule moves away, leaving its amino acid behind
translation
step four
a 3rd tRNA molecule binds to the next codon on the mRNA. its amino acid binds to the 1st 2 and the 2nd tRNA molecule moves away. this process continues, producing a chain of linked amino acids (polypeptide chain), until there’s a stop signal on the mRNA molecule
translation
step five
the polypeptide chain (protein) then moves away from the ribosome and translation is complete
what is the genetic code
the genetic code is the sequence of base triplets (codons) in mRNA which code for specific amino acids
why is genetic code non-overlapping?
base triplets don’t share their bases
why is the genetic code degenerate?
there are more possible combinations of triplets than there are amino acids (20 amino acids, 64 possible triplets)
what does the genetic code being degenerate do?
some amino acids are coded for by more than 1 base triplet
do all triplets code for amino acids
not all triplets code for amino acids
what are stop signals
some triplets are used to tell the cell when to stop production of a protein, found at the end of mRNA
what are start signals
tell the cell when to start protein production, found at the start of mRNA
what does it mean by the genetic code being universal
the same specific base triplets code for the same amino acid in all organisms
