Nucleic acids and protein synthesis Flashcards
structure and replication of DNA protein synthesis
nucleotide derivatives and their cellular role
ATP and GTP work with energy transfers in the cell
phosphate
represented via circles
form backbone of DNA or RNA molecule, linking neighbouring sugars
base
carries coded genetic message in nucleic acid
pyrimidines examples
cytosine
thymine
uracil
pyrimidines
single ringed bases
smaller than purines
purines
double ringed bases
examples of purines
guanine and adenine
sugar in dna
deoxyribose
sugar in rna
ribose
ATP
adenine triphosphate
provides chemical energy for metabolism, consisting of adenine linked to a ribose sugar and 3 phosphate groups
how is energy transferred from ATP
when a phosphate group is transferred to a target molecule
how are nucleotides formed?
phosphoric acid and a base are chemically bonded via a condensation reaction
reverse is hydrolysis
nucleic acids
macromolecules made up of long chains of nucleotides to transfer and store genetic info.
eg dna and rna
ribonucleic acid roles
read genetic info
how do dinucleotides form?
2 nucleotides are linked together via a condensation reaction between the phosphateof one nucleotide and the sugar of another.
which direction does dna replication work in?
the 5’-3’ direction
rna molecule
single strand of nucleotides linked together, often folded back in on itself.
uracil replaces thymine
ribose sugar replaces deoxyribose sugar
deoxyribose nucleic acid
double strand of nucleotides linked in atwisted double helix shape
asymmetrical and antiparallel structure
5 prime end of dna
terminal phosphate group off of carbon 5
3 prime end of dna
terminal hydroxyl group off carbon 3
what determines base pairs
the number of bonds available to form and the configuration of bases.
mRNA
transcribed from dna, carrying a copy of genetic info from the dna to the ribosomes to be translated into a polypeptide
tRNA
carries amino acids to thegrowing polypeptide chain, one end carrying the anticodon and the other an amino acid.
where does the amino acid link to in the tRNA
the 3 prime end
rRNA
ribosomal rna
forms ribosomes from 2 (large and small) subunits
evidence for structure of dna
x ray crystallography in which x rays are shone through crystallised molecules to produce a pattern on film.
eg photo 51 produced by Rosalind franklin and Maurice wilkins
what did photo 51 indicate of dna structure?
x pattern indicates helix structure
gaps indicate pattern of double helix and allows for calculation of the length of one full turn of helix
diamond spaces indicate a continuous and constant dimension with a sugar phosphate backbone outside the helix.
what does dna extraction buffer consist of?
water, detergent, salt
detergent purpose in buffer
breaks down cellular membrane and deactivates DNAases which would ordinarily chop up dna
salt purpose in buffer
removes proteins bound to dna and keeps them in solution while neutralising negative charge of dna.
ethanol purpose in buffer solution
enables dna to precipitate out aided by low temps which limit DNAase activity
semi conservative dna replication
produces 2 identical copies of dna, half original and half new material
hows the dna unwound in replication?
helicase unzips it at high speed at a replication fork while another enzyme prevents supercoiling
purpose of dna polymerase
catalyses the condensation reaction joining adjacent nucleotides.
what direction does dna polymerase work in
5’-3’ direction so that they are assembled continuously in one strand and fragmented as okazaki fragments (later joined by ligase)
purpose of dna replication
to double DNA, allowing each cell to have a complete set of genes before cell division.
3 main steps in replication
unwinding dna
synthesising dna polymerase
rewinding of the dna molecule
2 ways of correction within dna replication
proof-reading
mismatch repair
helicase purpose
unwinds and separates double stranded dna at replication fork at high speed.
RNA polymerase purpose in replication
synthesises a short RNA primer
DNA polymerase 3 purpose in replication
what direction does it go in?
extends the RNA primer with complimentary dna found from free nucleotides floating around via catalysing the condensation reaction between nucleotides.
moves in the 5’-3’ direction, synthesising the leading strand continuously.
DNA polymerase 1 purpose in replication
digests RNA primer to replace w dna
DNA ligase purpose in replication
joins neighbouring fragments together
how often are mistakes made in replication?
every 100000 nucleotides replicated
conservative model
DNA comprised 2 new strands
dispersive model
new and old dna mixed throughout them
generation 0
the sample removed of e coli bacteria after being grown in a nutrient broth containing N15 after 14 generations.
where is generation 0 put?
a solution containing excess N14 so that new dna incorporates the N14 with the N15 isotope.
Where is each generation placed?
in a CsCl solution which provides a density gradient for DNA separation
How high and long are samples spun in a centrifuge
at 14,000 g for 20 hours
genetic code
the set of rules by which the genetic info in DNA or mRNA is translated into proteins
codons
3 letter codes on mRNA, representing 1 of 20 amino acids used to make proteins.
degeneracy and where is it mostly located
the flexibility in which there may be more than one codon for each amino acid, mostly found in the 3rd nucleotide of a codon.
genes
sections of dna that code for proteins
gene expression
the process of rewriting a gene into a protein, involving transcriptionof DNA into mRNA before translating the mRNA into a protein.
where is a gene bounded?
at a promoter region upstream of the gene
where is a gene finished?
at a terminator region downstream of the gene
promoter region
where rna polymerase binds
terminator region
where rna polymerase dissasociates
where does translation stop and start?
at the start and stop codon
first amino acid
methionine
Gene mutations
Localised changes to the DNA sequence, able to produce new, heritable alleles.
Causes of mutations
Mutagens
Errors during replication
Deletion/substitution/ insertion of bases into DNA sequence leads to a single gene mutation
Mutation responsible for NSRD
Deletion of 35th base (G)
Cause of sickle cell disease
Substitution of one nucleotide from T to A
Gene mutation Hbs produces a faulty beta chain haemoglobin protein.
New amino acid is hydrophobic not hydrophilic so collapses in on itself when deprived of oxygen.
Sickle cell disease
Inherited blood disorder caused by gene mutation Hbs, producing deformed red blood cells with a reduced capacity to carry oxygen
Red blood cells
Contain 270 million haemoglobin molecules, have a flattened disc shape.
Made up of 2 alpha and 2 beta chains linked together.
Sickle cells
What do they cause?
Reduced solubility and precipitates when deprived of oxygen, preventing movement through capillaries.
Sickle cell anaemia is caused as rigid shape blocks small vessels and damages tissue and organs.
Relationship between sickle cell disease and malaria
Heterozygotes are less susceptible to malaria than unaffected as the parasite can’t affect deformed cells.
Therefore high frequency of it in malaria regions.
Where does transcription take place
Nucleus
DNA replication overview
Helicase
RNA polymerase primer
DNA polymerase 3 catalyses condensation reaction between amino acids
DNA polymerase digests RNA and replaces with DNA
Ligase joins neighbouring fragments
DNA rewinds
Enzyme controlling transcription
RNA polymerase forms a strand of mRNA from template strand, transcribing a gene length at a time, recognising start and stop signals.
What allows a high rate of mRNA synthesis to occur
Multiple RNA polymerase enzymes on one length of dna at any one time.
Introns
Non coding sections of mRNA that must be removed before translation can occur
Exons
Remaining dna that must be spliced together to form mature mRNA.
Where does transcription occur in prokaryotic cells
In the cytoplasm
Therefore is quicker
Antisense strand
The temp,ate strand that stores info transcribed into mRNA.
Transcription overview
RNA polymerase binds to a promoter region and joins rna nucleotides together, ending when it reaches a terminator sequence and final triplet is transcribed coding for stop.
Where does translation occur?
In the cytoplasm associated w free ribosomes/ the rough endoplasmic reticulum.
Where does the mRNA strand go after it leaves the nuclear pore?
Into the cytoplasm to attach to a ribosome.
tRNA structure
They have a triplet of bases at one end and a region for amino acids to attach at the other end.
Roughly 80 nucleotides in length.
tRNA role in translation
They pick up free amino acids and brings to ribosome, matching anticodon on tRNA w codon on mRNA (complimentary).
How many tRNA molecules fit onto the ribosome at any one time
2
What bonds are formed between amino acids in translation
Peptide bonds
Ribosomes structure
Made up of a complex of ribosomal RNA and proteins, existing as 2 separate subunits (large and small) until they are attracted to a binding site on mRNA.
Have binding sites that attract tRNA
Anticodon
The site of the 3 base sequence that matches up w the codon on mRNA.
