nucleic acids Flashcards
DNA nucleotides stucture
A phosphate group
5 carbon pentose sugar- deoxyribose
contains 1 of 4 nitrogenous bases: adenine Cytosine guanine thymine
RNA nucleotides
A phosphate group
5 carbon pentose sugar- ribose
1 of 4 bases: adenine cytosine guanine uracil
dinucleotide formation
condensation reaction between phosphate group and ribose(RNA) or deoxyribose(DNA) to form a phosodiester bond
either catalysed by RNA or DNA polymerase
polynucleotide formation
multiple mononucleotides are added via condensation reactions to form a long chain called a polynucleotide
resulting in many phosphodiester bonds forming creating a sugar phosphate backbone- stable and strong
added 5’ to 3’ by DNA polymerase
DNA double helix
2 polynucleotide chains held together by H bonds between specific comp base pairs
Adenine- Thymine 2bonds
cytosine- guanine 3bond
antiparrallel- one runs 5’ to 3’ other 3’ to 5’
Function+ structure of DNA
hold genetic info enabling info to pass through generations
comb of base pairs is almost infinite allowing for genetic diversity as all DNA base sequences are different
- sugar phoso backbone and double helix- strenght+ stability+ protects info coded in bases
2.long molecule- can store a lot of info
3.helix structure- compact
4.base sequences- codes for a acids and proteins
5.double stranded- allows for semi Conservative rep cause each strand=template
6.comp base pairs-allows accurate replication
7.H bonds between bases- easily broken and separation of strands for semi Conservative rep - Many H bonds- strong+ stable
Chargaffs base pairing rule for DNA
A-T 2H bonds
C-G 3H bonds
if given 1 strand of DNA we can work out base sequences of other strand by using this
If we are given percent of 1 base we can work out percent of other comp bases
A-25% then T-25%
so C+G=50%
50%/2=25%
so C-25% and G-25%
RNA- Ribonucleic acid
RNA is a polymer of RNA nucleotides. which include ribose sugar a phosphate group and 1 of 4 nitrogenous bases- Uracil, adenine, cytosine and guanine
is is a single polynucleotide chain and shorter than DNA
1.mRNA- Messenger RNA it is a single stranded linear polynucleotide. It is a stranded copy of a gene and takes info to ribsomes to make proteins
2.tRNA- transfer RNA single stranded folded cloverleaf shape. Brings A acids to ribsome during protein synthesis
3.rRNA- ribosomal RNA found in ribsome with proteins
semi Conservative replication
insure genetic info is same between cells so daughter cells can produce same proteins
step 1) you start with a normal portion of DNA
step2) 2 strands are separated by the breaking of H bonds between comp base pairs, this is catalysed by DNA helicase
step3) Each strand acts as a template and free DNA nucleotides are attached to expose comp base pairs, H bonds now form between como base pairs
step 4) DNA polymerase joins adjacent DNA nucleotides on new strand via condensation reactions forming phosodiester bonds
step 5) DNA lipase seals it
step 6) We are left with 2x DNA molecules that each contain 1 new stand and 1 original strand
why does DNA polymerase work 5’ to 3’
DNA polymerase has a specific active site that’s is comp to 5’ end of free nucleotides and the 3’ end of the new strand. This catalyses a condensation reaction forming a phosodiester bond between the last DNA nucleotide in the developing strand and the incoming DNA nucleotide and so synthesises 5’ to 3’
Watson and crick
discovered the structure of DNA which inspired the idea of semi Conservative replication model
what were the different models of DNA rep
Conservative- the original parent strand remains intact- completely conserved and a whole new DNA molecule is made
Semiconsevative- each new DNA molecule produced contained 1 og strand and 1 new strand
Dispersive- where each new DNA molecule contains fragments of both parental and new helix
The Meselson Stahl experiment
based their experiment on 3 things:
1.All DNA bases contain nitrogen
2. it has 2 isotopes N14 less dense and N15 more dense
3. Bacteria take up N from their enviroment to make all new DNA nucleotides during replication
Gen O- grew bacteria im medium containg N15 so all DNA contained only the more dense N15
they the broke open some of the cells using CsCl and centrifuges the DNA
found DNA formed 1 band at bottom of tube as more dense N15
Gen1- Took some of N15 bacteria and put them on a medium containing N14 and allowed cells to replicate
Broke one cells
formed 1 band in middle indicating equal mix of N14 and N15, destroyed conservative rep model
gen2- took some of gen 1 bacteria and put them inbN14 medium, allowed to rep
broke open
DNA formed 2 bands 1 in middle with equal parts N15 N 14 and second band at top DNA contains only N14 as it is less dense
Gen3+4- repeated steps and everytime more and more of DNA contained N14 only proving evidence for semi Conservative rep
ATP- Adenosine triphosphate
produced during respiration and is then used as main energy source in cells
structure- it is a nucleotide derivative:
1 nitrogen containing organic base- Adenine
1 ribose sugar
3 phosphate groups
they are joined via condensation reactions
ATP hydrolysis
ATP + H20 ——-> ADP + Pi + E
ADP- adenosine diphosphate
Pi- inorganic phosphate
carried out by ATP hydrolase
