3.1.5 nucleic acids Flashcards
Structure of DNA and RNA and DNA replication
What are the complimentary base pairs in DNA?
A and T
C and G
What are the complimentary base pairs in RNA?
A and U
C and G
How many hydrogen bonds are between A and T?
2
How many hydrogen bonds are between C and G
3
Which nitrogenous bases are purines
A and G
2 carbon rings
WHich nitrogenous bases are pyramidines
T, C and U
1 carbon ring
What does DNA stand for?
deoxyribose nucleic acid
What are the three comoponents of a nucleotide
nucleotides make up DNA
- nitrogenouse base
- phosphate
- deoxyribose sugar
How is a dinucleotide formed?
- condensation reaction
- bond is formed between C3 and phosphate
- phosphodiester bond
Describe and explain the 4 adaptations of DNA?
- Stability, maintains the sequence of genetic info, needs to last the lifetime of the cell
- Hydrogen bonds- strength and stability on mass, allows strands to be seperated for protein synthesis or replication
- Large molecule - stores all the genetic info
- Base pairs are on the inside of the molecule- protects genetic code
What are the uses of the two strands in DNA?
- Coding strand - order of nitrogenous bases on the coding strand codes the order of amino acids in the primary structure of a protein
- Non coding strand - provides two strands for DNA replication and protects the order of the bases
What are the components of RNA?
- ribose
- phosphate group
- nitrogenous base- adenine, uracil (instead of thymine), guanine cyastine
What are the three types of RNA?
- messenger RNA - carries genetic information from the DNA to the ribosomes
- transfer RNA - brings the amino acids to the ribosomes
- ribosomal RNA - produced in the nucleolis, forms a part of ribosomes
What are the differences between DNA and RNA?
- RNA is single stranded and DNA is double stranded
- RNA uses uracil in place of thymine
- RNA contains a ribose sugar and DNA contains a deoxyribose sugar
What is the structure of mRNA?
- Single stranded molecule
- Contains unpaired bases
- bases are arranged in codons (groups of three)
What is the structure of tRNA?
- single stranded molecule that folds into a specific shape
- Secondary structure is a clover leaf shape
- Tertiary structure is an L-shape
- Has anticodon region complimentary to the codons on mRNA
- attachment site for amino acids
What can increase the occurence of mutations in DNA
- X rays
- UV light
- Benzine
- Tobacco tar
How is DNA replicated
- semi conservative replication
- In each new DNA molecule, one polynucleotide strand is present from the original DNA molecule
What are the three types of mutations
addition - frameshift to the right
deletion - frameshift to the left
substitution
Why is the genetic code considered universal
- the same codons code for the same amino acids in all organisms
What is an intron and exon?
INTRON:
- The section of genetic code that is removed from the pre-mRNA during splicing
EXON
- The section of genetic code that is not removed from the pre-mRNA during splicing
Difference between bacterial DNA and eukaryotic and prokaryotic
- Circular instead of helix
- no introns in bacteria
- no histones in bacteria
- binary fission instead of mitosis
Transcription
Where one gene on the DNA is copied into mRNA
Translation
Where the mRNA joins with a ribosome and tRNA molecules bring the specific amino acid that each codon codes for
How does mRNA leave the nucleus
Nuclear pores
Transcription step by step
- The DNA helix unwinds to expose the bases to act as a template
- only one chain of the DNA acts as a templatelte, the coding strand
- the breaking of the hydrogen bonds between the two DNA strands is catalysed by DNA helicase
- mRNA nucleotides align opposite exposed complimentary base pairs on the DNA
- RNA polymerase bonds together the RNA nucleotides via phosphodiester bonds to create the pre-mRNA strand
Splicing
- the pre-mRNA strand contains intron and exons
- Introns are not coded for but exons are
- Splicing removes the intron form the pre-mRNA strand resulting in the mRNA strand
Translation step by step
- modified RNA leaves the nucleus via nuclear pores and attaches to a ribosome in the cytoplasm
- the ribosome attaches to the start codon and holds it in place for a tRNA molecule with a complimentary anti codon to attach
- the tRNA molecule has a specific amino acid attached to the top
- The ribosome will move along the mRNA chain so another tRNA can attach
- the ribosome catalyses the formation of peptide bonds between adjacent amino acids, this requires ATP
- the tRNA detaches and collects another amino acid
When does DNA replication occur
During the S phase of mitosis
DNA replication step by step
- DNA helicase unwinds the double helix strand which runs anti parallel, by breaking the hydrogen bonds between the bases
- Each polynucleotide strand acts as a template for the formation of a new strand, formed by nucleotides which are attracted to their complimentary base pairs
- The new nucleotides are joined together by DNA polymerase which catalyses the condensation reaction of the phosphodiester bond
- The original and new strand join together via hydrogen bonding between the base pairs
- this is called semi conservative replication
How does DNA polymerase work
- The bases of the free nucleoside triphosphates align withtheir complimentary base pairs on each of the template strands of the DNA
- The enzyme DNA polymerase synthesises new DNA strands from the two template strands
- It does this by catalysing the condensation reaction between the C3 of the deoxyribose sugar and the phosphate groups of the adjacent nucleotides
- This creates the sugar phosphate backbone of the new DNA strands
- DNA polymerase breaks off the two extra phosphates and uses the released energy to create the phosphodiester bonds
What is semi conservative replication
- One strand from the original DNA is conserved
- The other strand is synthesised by the cell
- Half of the original DNA is conserved in order to create a new DNA molecule
What is the importance of semi conservative replication of DNA
- It ensures that all the genetic material is inherited from its parent cell
- Genetic continuity
