Nucleotides Flashcards
What does a nucleotide consist of
Base (nitrogenous)
Phosphate group
Pentose sugar
In summary elements they consist of are C,H,O,N,P
What are the differences between DNA and RNA
- in DNA sugar = deoxyribose
RNA= ribose - in DNA there are 4 different bases (A,G,C,T)
RNA doesn’t contains 4 bases but instead of T it is Uracil
How is a polynucleotide formed and what is the bond called
When you take 2 nucleotides you form a bond between one phosphate group of one nucleotide and one hydroxyl group on carbon 3 of the other nucleotide
-called phosphodiester bond
What is a purine
Has 2 rings
What is a pyrimidine
Has 1 ring
Describe the structure of DNA
-2 polynucleotide strands held by H bonds (bases in middle sugar phosphate backbone on outside)
(Bases on one strand are complementary to the base on the other)
- antiparallel
-form double helix
-connects by 3’C and 5’C
How do we work out proportions of bases in DNA
-complementary base pairing allow it to
-if it says in a question 20%is guanine then cytosine must also be 20% bc of base pairing
-then the rest of the bases should be 60% which is adenine and thymine so they should be 30% bc of base pairing
-there proportions are equal to there complementary bases
What are the complementary base pairings and how many H bonds do they form with each other
Adenine with thymine - 2bonds
Cytosine with guanine- 3bonds
Describe the structure of RNA
-contains ribose
-doesn’t have thymine instead it is uracil
-
What are the key differences between DNA and RNA
-DNA found in nucleus in chromosomes
-RNA found in cytoplasm
-DNA is very long molec
-RNA is a short molecule
-DNA has double strands
-RNA has single strands
Describe the stages of DNA replication
-DNA helicase attaches to the DNA and causes H bonds to break the 2 strands unzip
-the free nucleotides line up with their complementary bases on the dna strand
-the activated nucleotides are lined up and held in place by H bonds between the complementary base pairs
-DNA polymerase attaches and moves down the molecule and catalyses the formation of a phosphodiester bond between the active nucleotides
-when phosphodiester bond is created the extra 2 phosphate groups leave the activated nucleotides and provided energy for the reaction
-we have 2 copies of the double stranded molc one is the original strand and one is the new strand (semi conservative replication)
What is semi conservative replication
-there is one original strand and one brand new strand
What is conservative replication
DNA double helix is formed containing two new strands
None of the original dna is in there
Nitrogen in DNA
Bases contain nitrogen
There are 2:
Nitrogen 14 and nitrogen 15, N-14 is light whilst N-15 is heavy
Explain the experiment of showing semi conservative vs conservative
-under normal conditions almost all of the N atoms in the DNA of the bacteria are N-14
-scientists took some of the bacteria and extracted the DNA
-they placed it in a solution and spun it in high speeds in a centrifuge
-the DNA moved down the solution and formed a band which the scientists could detect (position of DNA band depends on how heavy the DNA is)
-then they cultured bacteria which contained only N-15
-after the bacteria reproduced many times all of the N atoms were N-15
-it formed a lie at the bottom of the tube after being centrifuged
-they then took a sample of bacteria that had growing N-15 and transferred these bacteria to N-14 and slowed them to replicate the DNA only once
-they they extracted the DNA and centrifuged they found that the DNA produced a band between the 2 bands produced before
-showed that the DNA produced one strand with N-14 and the other with N-15
-this means the DNA had replicated semi conservatively
-after replicating with N-14 again there were 2 bands
What would results show if dna replicated conservatively than semi conservatively
-After 1 round of replication we would have 2 strands that have M-15
And one molc only containing N-14
-after 2 replications we would have 1 molc of DNA containing only N-15 but have 3 molc of DNA containing Nx14
Prokaryotic vs eukaryotic dna
Chromosomes
What are the 2 main stages of protein synthesis
-transcription and translation
Explain the process of transcription
-takes place in nucleus
-the sequence of the gene is copied into the mRNA
-the mRNA moves into the cytoplasm the information encoded in the mRNA is used to join a specific order of amino acids forming a polypeptide (translation)
-helicase breaks the H bonds between the 2 strands
-now complementary RNA moves into place forms H bonds with the bases of the exposed nucleotide
-RNA polymerase joins the RNA nucleotides by forming phosphodiester bonds
-now mRNA is produced after synthesis of mRNA the DNA goes back into a double helix and then the mRNA leaves the nuclear pore to take part in translation
What is non overlapping
-no base is read more than once
What is degenerate
-a single amino acid can be coded by more than one codon
What is universal
- the same triplets code the same amino acid in the vast majority of species
Stages of translation
-each triplet in the mRNA aid called a codon
-tRNA top has a binding site and bottom we have triplet of bases called anti codon
-tRNA is complementary to the MRNA
