how DNA works, genetic code, protein synthesis Flashcards
who found the double helix model
watson and crick
conservative replication
in conservative replication, the original double helix remained intact and in some way instructed the formation of a new identical double helix made up of entirely new material
semiconservative replication model
assumed that the dna unzipped and new nucleotides aligned along each strand, each new double helix contained one strand of the original dna and one strand made up of new material.
who proved semi conservative replication
mselson and stahl
steps of the semi conservative replication experiment
-grew generations of ecoli bacteria in nitrogenous medium
bacteria took up isotope to make cell chemicals including dna and proteins
-moved to N14 medium
-measured density of dna and they produced
what isotopes were used for the ecoli bacteria
N 15 and N14
which isotope is usually denser
N 15 rather than the commonly found N14
what isotope base were the bacteria first placed in
N15 and then moved to N14
what would the results look like if DNA replicated conservativly
some of the dna would have the density expected if it had nothing but N 15 and some would have nothing but density of N 14
what were the results proving semi conservative replication
all of dna would have same density half of N14 and half of N 15
role of DNA helicase
the two strands of the dna molecule unzip along the line of hydrogen bonds and unravel. the strand acts as a template for the new dna strands
role of DNA polymerase
exposed bases attract free DNA nucleotides and new hydrogen bonds are formed between matching base pairs. polymerase lines up and catalyses the linking up of the nucleotides along the template strand
role of DNA ligase
catalyses the formation of phosphodiester bonds between the two strands of DNA
whats the result of DNA replication
two new strands of DNA identical with original strand, new molecules coil up into double helix as weak hydrogen bonds form within the structure
whats the genetic code
means that three bases are a triplet code that code for one amino acid
define genes
gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain that affect the charesteristic in the phenotype of an organism
whats a codon
a sequence of three bases on the DNA or RNA
what happens because of codons on DNA being to big
because codons on DNA are difficult to work with because they are so big the work done on codons is on codons of smaller molecule mRNA
what is this mRNA formed as
a complementary strand to the DNA like a reverse image of original base sequence
how can we know DNA pairs with RNA pairs
because we work out the complementary bases
what do studies about genetic code suggest
that almost all genetic code in humans is identical
whats non coding DNA
large parts of the DNA that dont code for protein and make up most of codings
translation
process by which proteins are produced via RNA using genetic code found in DNA and takes place in ribosomes
a non overlapping code
only one codon codes for one amino acid meaning if they were to overlap it would only effect one amino acid
a degenerate code
the base of the amino acids producing only matters with the first two bases meaning if there was a mutation occured in the last base it wouldnt effect the amino acid produced
what differs RNA and DNA
RNA has ribose
no double helix
uracil instead of thymine
3 main roles of RNA in protein synthesis
1- it carries instructions for a polypeptide from the DNA in the nucleus to the ribosomes where the proteins are made
2-picks up specific amino acids from the protoplasm and carried them to surface of ribosomes
3-makes up bulk of ribosomes themselves
where is mRNA formed
in the nucleus
what does mRNA carry insturcions for
one polypeptide chain
antisense strand
the mRNA template strand
sense strand
the coding strand of DNA
DNA directed RNA polymerase
parts of DNA molecule unravel and are transcribed onto strands of mRNA by that enzyme
how is another strand of mRNA formed
the complementary bases of DNA and RNA line up alongside each other. RNA nucleotides from the nucleoplasm line up alongside the exposed DNA. initial hydrogen bonds replaced by phosphodiester bonds catalysed by RNA polymerase to form strand of mRNA
what does the mRNA molecule do after being made
passes through the nuclear pores carrying the instructions for the genes in the nucleus to the cytoplasm. they then move to the surface of the ribosomes where the protein synthesis takes place
transcription definiton
copying a part of DNA into RNA
where is tRNA found
in the cytoplasm
what shape is the tRNA often described as
clover shape
why does the tRNA have clover shape
result of hydrogen bonds between different bases
anticodon
on part of tRNA molecule has sequence of three bases that match genetic code of DNA and correspond for one amino acid. sequence of three bases is an anticodon
binding site in tRNA
which it picks up one particular amino acid from lots always free in the cytoplasm
what do tRNA molecules line up with
mRNA molecules
anticodons of the tRNA role
line up with mRNA codons held in place with hydrogen bonds with each complementary base
what happens once the amino acids are lined up with each other
peptide bonds form between then building longer chain of amino acids
where is rRNA made
made in the nucleus under the control of the nucleoli
role of rRNA after being made
moves out into the cytoplasm from the nucleus where it binds with proteins to form ribosomes.
structure of ribosomes in rRNA
made of small and large subunit
-surround and bind to parts of the mRNA that are being translated and move along to the next codon
job of ribosomes in rRNA
hold together the mRNA AND tRNA and act as enzymes controlling process of protein synthesis
protein synthesis summary
DNA of nucleus transcribed into mRNA
-mRNA moves into cytoplasm and attached to ribosomes
-molecules of tRNA carry out separate amino acids to surface of ribosome
-tRNA anticodon with codon mRNA and link amino acids together with peptide bonds
-tRNA breaks off and gets another amino acid
-ribosomesw move along molecule of mRNA and leaves a completed polypeptide chain
describe structure of mononucleotides found in RNA
has sugar like ribose pentose and phosphate group and nitrogenous base like A C G T U
how cystic fibrosis effects person as a result of point mutation
-different amino acid/primary structure
-change in shape/function of protein
-role of protein in taking chlorine ions
-ions not moving out of cell and water moves in via osmosis
-musus not dilluted with water
thick musuc cant be removed via coughing and cillia
ways gene therapy could be used to treat cystic fibrosis
introducing genes to lungs that can make musus
via injection
repeated because of cell reproduction
using a vector
how scientists find other works
scientific peer reviewed journals
media reports
2 parts that form mononucleotides
deoxyribose and phosphate
translation of mRNA results in polypeptide chain
each tRNA molecule attached to one AA
tRNA anticodon with each AA
codons on mRNA
hyrdogen bonds between strands
peptide bonds between chains formed
non overlapping defiintion
each base only used once in a triplet code
importance of codes stop
stop codons
occur at end of gene code
transcrobed by mRNA into opposite strand
recognised by ribosome
signal end of peptide chain
how are amino acids joined together in a polypeptide chain
peptide bond
between cooh and na
condensation reaction
role of tRNA in joining amino acids together
how molecule of mRNA is made during transcription
-DNA molecule unwinds
-RNA mononucleotides line up against antisense strand
-base pairing
-phospodiester bonds
-condensation reaction
-mRNA detached form DNA
how structure of tRNA differs from mRNA structure
-tRNA folded and mRNA straight
-tRNA has hydrogen bonds mRNA doesnt
-tRNA has anticodons but mRNA had codons
why can DNA be described as a double bonded polynucleotide chain
two strands
strands joined by hydrogen bonds
many nucleotides
nucleotides joined by phosphodiester bonds
describe structure of amino acid
amine group
r group
carboxyl group
explain how RNA templates used to specify the chemical structure of a protein
-triplet code is code for amino acid
mRNA binds to ribosome and codon
tRNA decoded M and gives right sequence for AA
-two tRNA sites in ribosome
-two AA brought together with peptide bond
-sections of DNA templates for RNA
