Nucleic Acids Flashcards
What bonds are present between bases?
Hydrogen bonds
What bonds are present between the sugar and phosphate group?
Phosphodiester bonds
What does a nucleotide consist of?
A nitrogenous base
A pentode sugar
A phosphate group
What does the backbone of a DNA molecule consist of?
A phosphate group
A deoxyribose sugar
How are phosphodiester bonds broken?
Hydrolysis
What is the structure of ATP?
Composed of an adenine base, a ribose sugar and 3 phosphate groups
ATP + H20 -> ADP + Pi + energy (hydrolysis)
Properties = small and water soluble
Give 4 reasons why ATP is useful
1- Releases energy in small amounts
2- Broken down in a single reaction, releasing energy quickly
3- Adds phosphate to other molecules, makes them more reactive
4- Easily resynthesised
What are pyrimidines?
Contain single carbon ring structures (hexagon)
Made up of carbon and nitrogen
Thymine and Cytosine
What are purines?
Contain double carbon ring structures (hexagon and pentagon)
Made up of carbon and nitrogen
Adenine and Guanine
How many hydrogen bonds are between adenine and thymine?
2 h bonds
Complementary base pairing
How many hydrogen bonds are between cytosine and guanine?
3 h bonds
Complementary base pairing
Base pairing
- Adenine and Thymine (2 h bonds)
Cytosine and Guanine (3 h bonds) - Small pyrimidine bases always bind to larger purine bases (parallel)
- Means that DNA always has equal amounts of all bases
What is a gene?
A section of DNA that contains the complete sequence of DNA to code for an entire protein
How is the genetic code degenerate?
There are more possible codes than there are amino acids (20)
Same amino acid can be coded for by more than one triplet
How is the genetic code universal?
- Codes for the same a.a in all living organisms
All organisms use this same code - all life on earth has common ancestory
How is the genetic code non-overlapping?
Each DNA triplet and gene is separate from each other
Describe semi conservative DNA replication
- DNA helicase unwinds DNA by breaking H bonds
- Both strands act as templates
- Free DNA nucleotides attach by complementary base pairing
- DNA polymerase joins nucleotides, forming phosphodiester bonds
- H bonds reform
- DNA replication is semi conservative (new DNA contains one old strand and one new strand)
What is the function of DNA helicase?
Unwinds DNA by breaking H to bonds
What is the function of DNA polymerase
It catalyses the condensation reaction between the nucleotides in a DNA strand
It forms phosphodiester bonds between adjacent nucleotides
What is the function of DNA Ligase?
Seals up the fragments in the sugar-phosphate backbone to form continuous DNA
What does primase do?
Makes a small piece of RNA called a primer
Describe Meselsohn-Stahl experiment
- population cultured in a growth medium containing heavy nitrogen (15N) only
- When centrifuged, only 1 heavy band is observed
- Cells transferred to a medium with only light nitrogen (14N)
- After 1 replication the DNA band was intermediate (twice the thickness)
- After 2 replications, intermediate and light bands were observed
Where does transcription take place?
Nucleus
Why is transcription important?
Makes a shorter mRNA molecule so that it can leave the nucleus and travel to the ribosomes
What is the process of transcription?
- DNA helicase unwinds strands by breaking H bonds
- Free RNA nucleotides attach to template strand
- Complementary base pairing
- RNA polymerase joins nucleotides together
- H bonds reform
- Once the mRNA strand is formed, it can move out of the nucleus and travel to the ribosomes (either free or those on the RER)
What are introns?
Non-coding sections of DNA
What is splicing?
Removing introns
What is the process of translation?
- Ribosome binds onto the mRNA at a start codon
- Codon is matched to an anticodon by complementary base pairing
- Ribosome holds tRNA in place
- Amino acids are joined together with a peptide bond
- Only 2 tRNA molecules can do this at a time
- Once the bond is formed, it moves onto the next 2 until it has a chain of amino acids (primary structure of a protein/polypeptide)
Where does translation take place?
Cytoplasm
Describe the method of purifying DNA by precipitation
1- Break open cells, e.g. blender
2- Mix: washing up detergent (break down nuclear membrane), table salt (Clump together pieces of DNA) and distilled water
3- Mix in cell mixture and wait 10 mins
4- Keep ice cold (stop enzymes breaking down DNA)
5- Filter mixture
6- Slowly pour cold ethanol to form a layer on top
7- Wait 10 mins
8- DNA forms a white precipitate
9- Remove DNA (tweezers/centrifuge)
What is a codon?
Triplet of bases on mRNA that codes for a specific amino acid
What is an anticodon?
Triplet of bases that is complementary to codon on mRNA
Describe tRNA
- Polynucleotide
- Folded by H bonds
- Anticodon is specific to amino acid that it carries
What is the DNA antisense strand?
- Template stand
- Acts as the template for mRNA
- Complementary to genes on sense strand
What is the DNA sense strand?
- Contains the genes
- Doesn’t act as the template for mRNA
What is the primary mRNA?
Same as DNA sense strand except U replaces T
What is the locus?
Location of gene on a chromosome
