Chapter 6: Protein Synthesis Flashcards
2 types of genetic material
DNA and RNA
what are DNA and RNA
macromolecules ie polymers made of repeated monomer nucleotides (polynucleotides)
difference between dna and rna
dna is double stranded
rna is single
important features of genetic material
it carries genetic info in form of genes that are responsible for characters
it is able to be copied when cell divides into daughter cells
components of a nucleotides
phosphate group pentose sugar (deoxyribose/ribose) nitrogenous base (A,T/U,G,C)
difference between deoxyribose and ribose sugars
at position 2 carbon instead of hydroxyl group in ribose we find hydrogen in deoxyribose
recall structure
study structures of phosphate and both sugars and somewhat that of purines and pyramidines bases
okur
which of A T/U G C are purines and pyramidines
Purines- A, G
Pyrimidines- T/U, C
bonds between bases
hydrogen bonds
A double bond T
G triple bond C
why do purines only link with pyramidines and vice versa but not with their alike bases
- purines are bigger molecules than pyramidines
- in a dna double strand there is just enough room between the 2 strands for a purine and pyramidine
- 2 purines will be too big and 2 pyramidines will be too small too fit in between
structure of DNA
- double stranded
- antiparallel in orientation (3’ to 5’ and 5’ to 3’)
- 3’-5’ phosphodiester bond backbone
- 2 strands held together by hydrogen bonds (nature) between bases via complementary base pairing
gene expression ie from dna to protein
DNA replicated this is catalysed by DNA polymerase
DNA transcripted to RNA this is catalysed by RNA polymerase
RNA is translated into protein
state the 3 models of DNA replication
- conservative
- semiconservative
- dispersive
describe the 3 models of DNA replication
- conservative: one fully new double helix daughter DNA made from one old parent, which doesnt change
- semiconservative: 2 new molecules each contain one old parental strand and one new complementary daughter strand. H bonds broken
- dispersive: new molecule made of bits of old and new bits randomly scattered
experimental evidence for the semiconservative model
- meselson and stahl supplied E.coli bacteria with NH4Cl and N-15 isotope initially
- left in NH4Cl to divide so almost all DNA had N15
- then transferred to N14 medium for 3 gens
- then this was centrifuged in caesium chloride solution
- results of bacteria grown in only N15 had a band of DNA
- then for those grown in N14 1st gen there is one thick band of DNA above then previous one
- then for 2nd gen with N14 there were 2 bands (equal)
- then for 3rd gen grown with N14 there was a thin band below and thick band above
explanation for results of the centrifuging of gens.
remember n15 is heavier than n14. use this to explain the bands
- initial dna made to 2 n15 strands daughter
- that replicated again to make 2 new dna each of 1 n15 and 1 n14 strands
- those replicate to 4 dna. 2 are of 1 n15 and 1 n14 strands. other 2 are both n14 strands only
- these 4 again lastly replicated to give 8 dna. 2 are of 1 n15 and 1 n14. 6 are of only n14 .
now relate this to the bands in previous fc
mechanism for dna replication
1) dna double helix unwinds and unzips as h bonds break
2) in nucleus, free activated nucleotides with 2 extra phosphates which activate and enable them to take part in reactions
3) bases on act.nucl. pair up with complementary bases on each old strand.
4) enzyme dna polymerase links sugar and phosphate of neighbouring molecules together. (only linked if bases are complementary. so errors are like 1 in ever 10^8)
5) phosphates broken off and released to nucleus
6) enzyme polymerises act.nucl. comp to nucls of comp strand in 5’-3’ orientation
mRNA function
carries message from DNA to ribosome for protein synthesis
mrna synthesis direction
5’-3’
mrna formulation occurs complementary to which dna strand and which enyzyme catalyses this
template/sense strand which is 3’-5’
rna polymerase
rRNA is present _ and has _ strands and function is
in ribosomes along with protein
single stranded
helps in protein synthesis
ribosome made up of
large and small subunits, made of rRNA and proteins
tRNA is found in
cytoplasm
structure of tRNA
- single stranded polynucleotide chain thats folded into a clover shape
- runs 5’-3’ where 5’ is start of strand and ends with phosphate, and 3’ is amino acid attachment site and has CCA bases overhang always
- at the bottom there are different anticodons loop ie 3 bases comp to mrna codon bases
- some h bonds create some areas of base pairing within strand
function of trna
transfer amino acids from cytoplasm to ribosome for protein synthesis
what are polyribosomes
in prokaryotes many ribosomes work on same mrna strand at same time to translate it
differences in translation between pro and eu karyotes
1) in pro tc and tl are simultaneous as nucleus is not bounded by membrane, in eu its not due to membrane
2) in pro 70s ribosomes involved, in eu its 80s
3) in pro mrna is in cytoplasm, in eu its in nucleus
4) in pro its fast, eu is slow
james watson and crick model of dna as in size of height and width of turns
how many bp per turn
width- 2nm
height- 0.34nm
10bp
what is the chargaff rule
A=T and G=C as in amounts of each
so
A/T=G/C=1
why is rna more reactive than dna
hydroxyl group at position 2 carbon of ribose makes rna more sensitive
rna is single stranded while dna is double
structure of ATP
adenine base attached to sugar which makes the nucleoside called adenosine
when this is attached to 3 phosphate groups it is ATP a nucleotide
check structure picture
difference between atp and dna
pentose sugar in atp is ribose, dna is deoxyribose
atp has 3 phosphates, dna has 1
atp has adenine base, dna has ATGC
difference between atp and rna
atp has 3 phosphates, dna is has 1
atp has adenine base, rna has AUGC
difference between nucleotide and nucleoside
nt=pentose sugar+base+phosphate
ns+pentose sugar+base
what is mutation
alteration in gene sequences where genes code for character, so mutation codes for altered character
alternate form of gene called
allele
dna and rna are polymers of _ and proteins are polymers of _
nucleotides
amino acids
what do proteins do
control cell activities eg enzymes catalyse metabolic reactions
sickle cell anaemia is
- autosomal recessive disorder
- on chromosome no 11 (an autosome)
- due to base substitution mutation in DNA where CTT coding hydrophilic glutamine replaced with CAT coding hydrophobic valine amino acid
- hence at position 6 of beta polypeptide chain theres a hydrophobic amino acid which changes circular rbc into a sickle shaped rbc
what is translation
conversion of nucleotide sequence of mRNA to amino acid sequence of protein
genetic code of amino acid
3 nucleotides ie bases
expression used to find total no of amino acids in the world
4^n where 4 is no. of known nucleotides and n is no. of nucleotides coding for an amino acid ie 3
so 4^3=64 but only 20 aa in the world. this is because different base combinations can code for the same amino acid