(2) Nucleotides and nucleic acids Flashcards
Structure of a nucleotide.
Made from pentose sugar, nitrogenous base and phosphate group.
Contains: C,P,O,N,H
It is a monomer which is used to make up nucleic acids.
Differences between DNA and RNA
DNA forms genetic material and RNA transfers this genetic material from DNA to the ribosomes.
Ribosomes are formed from RNA and protein.
RNA has ribose, DNA has deoxyribose (one less o2).
RNA is single stranded, DNA is double stranded.
RNA uses uracil, DNA uses thymine
Purines and prymidines
Purine contains 2 carbon nitrogen rings joined together - adenine and guanine
Prymidines only have one carbon nitrogen ring, so is smaller - cytosine and thymine.
Types of pentose sugar
Ribose - found in RNA
Deoxyribose - found in DNA, contains one less o2 than ribose.
Polynucleotides
Pentose sugar and organic base join in condensation reaction, removes water to create nucleoside.
Then pentose of nucleoside joins with a phosphate group by another condensation reactions, forming a nucleotide.
Then pentose of one nucleotide joined with the phosphate of another by a condensation reaction to form a dinucleotide.
Further condensation reactions forms a polynucleotide and 2 pentose sugars join by the phosphate with a phosphodiester bond.
ADP and ATP
ADP and ATP are phosphorylated nucleotides.
ATP is synthesised from ADP and inorganic phosphate using energy from an energy releasing reaction.
ADP is phosphorylated from ATP and a phosphate bond is formed. Energy is stored in the bond ans when energy is needed by a cell, ATP is broken back down into ADP and Pi, energy released by the phosphate bind us used by the cell.
ADP + Pi into ATP uses energy
ATP into ADP + Pi releases energy.
Structure of DNA
Nucleotides join with phosphodiester bonds to form polynucleotides.
Chain of sugar and phosphates = sugar phosphate backbone.
2 polynucleotide strains join together by hydrogen bonding between the bases via complementary base pairing (A and T, C and G).
2 hydrogen bonds between A and T and 3 between C and G.
2 anti parallel strands twist together to form the DNA double helix.
Purifying DNA
Using a precipitation reaction.
Break up cells of sample.
Add detergent (breaks down membrane), salt (binds to DNA causing it to clump together) and distilled water.
Add everything to a beaker and heat in a water bath at 60’ for 15 mins. Temperature stocks the enzymes from breaking down the DNA.
Then out into ice bath and filter the mixture.
Add protease enzyme to filtered mixture, to break down proteins.
Add cool ethanol to the side of the tube so it forms a layer on top of the mixture.
Leave for a few mins and DNA with form a white precipitate which can be removed with a glass rod.
Semi conservative DNA replication
Copied before cell division.
DNA helicase breaks the hydrogen bonds between the 2 polynucleotide DNA strands and unzips the helix.
Each original strand acts as a template for a new strand and free floating nucleotides join to the enclosed bases by complementary base paring.
New strands are joined together with DNA polymerase forming sugar phosphate backbone, hydrogen bonds form and twist together to make a double helix.
Each new molecule has one old strand and one new strand - semi conservative.
Must be accurate to make sure genetic information is conserved each time the cell is replicated.
Sometimes random mutations occur which causes a change to the base sequence, sometimes alters the sequence of amino acids in proteins, causing an abnormal protein to be made which may function better or worse than the original.
Genetic code
Sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids.
Each triplet is separate from the triplet before and after it, they do not share there bases therefore the code is non overlapping.
It is also degenerate meaning there are more possible combinations of triplets than there are amino acids. So some amino acids are coded for by more than one base triplet.
Some triplets are used to tell the cell when to start and stop the production of the protein.
Genetic code is universal - the same specific bases for the same amino acids are in al, living things.
Types of RNA
Ribosomal RNA (rRNA) - large molecule, forms some of the mass of the ribosome, rip some moves along mRNA strand during protein synthesis and rRNA helps catalyse the formation of peptide bonds between the amino acids.
Messenger RNA (mRNA) - made in the nucleus carries the genetic code from the DNA into the nucleus to the cytoplasm where it’s used to make a protein during translation.
Transfer RNA (tRNA) - found in cytoplasm, has an amino acid binding site at one end and sequence of 3 bases on the other (anticodon). Carries the amino acids that are used to make proteins to the ribosomes during translation.
Transcription
mRNA copy of a gene is made in the nucleus.
Starts when RNA polymerase attaches to the DNA double helix at the beginning of a gene. Hydrogen bonds break, separating the strands. One strand acts as a template to make an mRNA copy.
RNA polymerase lines up free RNA nucleotides along the template strand, complementary base pairing means that the mRNA strand is complementary copy of the DNA template. T is replaced with U.
Then bases are joined together forming mRNA.
RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand. Hydrogen bonds between the uncoiled strands reform once the RNA polymerase has gone and the strand coils back to double helix.
When RNA polymerase reaches stop codon, it stops making mRNA and detaches from DNA. mRNA moves out of the nucleus through nuclear pore and attaches to ribosome in the cytoplasm.
Translation
Occurs at the ribosomes in the cytoplasm. Amino acids are joined together to make a polypeptide chain, following the sequence of codons.
mRNA attached to ribosome, tRNA carries amino acids to the ribosome. It has a complementary anticodon to the start codon on the mRNA, which is attached by complementary base pairing.
Next tRNA attaches in the same way. rRNA in the ribosome catalyses the formation of the peptide bond between the 2 amino acids, joining them together. tRNA moves away, leaving the amino acid behind.
This process continues, producing a chain of amino acids until there is a stop codon. The the polypeptide chain moves away and translation is complete.
