Nucleic Acids And DNA Replication Flashcards
Nucleotide structure
Phosphate group
Pentode sugar (ribose or deoxyribose)
Nitrogen base
How are the 3 components in a nucleotide joined together
Condensation reaction
Pyrimidines vs purines
Pyrimidines, 1 carbon circle = cytosine and thymine
Purines, 2 carbon circles = adenine and guanine
How do two mono nucleotides join to form a di-nucleotide
Covalent phosphodiester bond forms between the phosphate group of one nucleotide and the pentose sugar of another.
These bonds formed through condensation recitations, which are catalysed by polymerase enzymes.
Many nucleotides must join together to form a polynucleotide chain.
Describe DNA’s antiparallel nucleotide strands
One strand runs in 5–>3 direction and the other runs in 3–>5 direction
Why would a section of DNA with more C-G pairs than A-T pairs take more energy to unwind?
Because C-G have 3 hydrogen bonds that join them together whereas A-T have 2 hydrogen bond that join them together so more energy required to break C-G hydrogen bonds as theres one hydrogen bonds more present so more energy required.
How does the structure of DNA allow it to carry out its function?
Sugar phosphate backbone and double stranded helix structure - provides strength and stability, protects bases and hydrogen bonding between bases.
Long molecule - can store lots of information
Double stranded helix structure - compact
Base sequence - codes for amino acids so proteins can be made
Complementary A-T and C-G base pairing - allows accurate replication
Hydrogen bonds between bases are weak - allows unzipping and separating of strands for replication
Many hydrogen bonds in the whole molecule - strong and stable molecule
DNA vs RNA
DNA - 2 strands of genetic information, RNA - 1 strand of genetic information
DNA - double helix structure, RNA - no double helix structure
DNA - has deoxyribose sugar, RNA- has ribose sugar
DNA - thymine bonded to adenine, RNA - uracil bonded to adenine
DNA - longer, RNA - shorter
DNA - holds genetic information, RNA - transfer genetic information from DNA to the ribosomes to turn into protein.
What did Watson and Crick do?
Determined double stranded helical structure, used X-ray diffraction.
What’s conservative replication
Completely new strand that is identical to original strand is formed
Semi-conservative model experiments
- In 2 test tubes (one containing N14, the other N15) place them in a centrifuge which will allow the lighter N14 band to form higher than the N15.
- To a N15 sample, place in a bacteria growth medium containing just N14.
- The DNA’s 1st replication will produce 2 identical DNA strands, containing 1 N14 and 1 N15 strand. If placed in a centrifuge its ring will form in between the N14 and N15 samples.
- The 2nd replication will produce 2 strands made of only N14 and 2 made from 1 N14 and 1 N15 strand. When this sample is placed in the centrifuge it will separate to produce 2 DNA rings rather than 1 as the 2 types of strands are different in weight.
- This is semi-conservative model
DNA replication (semi-conservative model)
DNA helicase breaks the hydrogen bonds between complementary bases. This causes the 2 strands of DNA to separate. The point at which the strands separate is called the replication form.
Both strands of DNA act as a template
Free nucleotides, which have been activated, are attached to their complementary bases (adenine to thymine and guanine to cytosine) and hydrogen bonds reform.
DNA polymerase reforms the phosphodiester bonds between adjacent nucleotides through condensation reactions. This reforms the sugar phosphate backbone.
2 new strands of DNA are formed each containing 1 original parent strand and one new daughter strand.
This is called the semi conservative replication model.
What’s DNA like in prokaryotic cells?
Short
Circular
Not associated with proteins
What’s DNA like in eukaryotic cells?
In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones.
Together a DNA molecule and its associated proteins form a chromosome.
What organelles contain DNA?
The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.
What is a gene?
Base sequence of DNA that codes for:
1. Amino acid sequence on polypeptide
2. A functional RNA (including ribosomal RNA and tRNA’s)
What does a gene occupy?
A fixed position (locus) on a particular DNA molecule
What’s a sequence of 3 DNA bases called?
Triplet
What does a triplet code for?
A specific amino acid
The genetic code is universal. What does that mean?
Same codon codes for same amino acid in each organism
The genetic code is degenerate. What does that mean?
Many codons for the same amino acids
The genetic code is non-overlapping. What does that mean?
Each base is only part of 1 codon
The genetic code involves non-coding stop codons. What does this mean?
Tell RNA polymerase to stop transcribing
Describe transcription
The hydrogen bonds between complementary base pairs on the 2 strands of DNA break as the 2 strands separate, by RNA polymerase.
One of the strands acts as a template.
Free RNA nucleotides are attracted to the exposed bases via complementary base pairing: adenine to uracil and cytosine to guanine.
RNA polymerase moves along the template strand, joining adjacent RNA nucleotides through condensation reaction forming phosphodiester bonds.
This continues until stop codon is reached, at which point RNA polymerase detaches.
The forms pre-mRNA.
Hydrogen bonds reform between the complementary bases on teh 2 DNA strands, and the double helix reforms.
What happens to pre-mRNA to turn into mRNA
Splicing as the introns (non-coding DNA) is removed
What is splicing
When the non-coding parts of DNA are removed
Introns vs exons
Introns = non-coding DNA
Exons = coding DNA
How is prokaryotic transcription different to eukaryotic transcription?
Prokaryotic = no splicing as no introns
Prokaryotic = translations and transcription happen at the same time
What is translation - simple definition?
The production of a polypeptide chains from the sequence of codons on an mRNA strand
Describe translation
mRNA attaches to a ribosome (on RER).
tRNA, carrying a specific amino acid binds to the mRNA. Anticodon on the tRNA complementary to the codon on mRNA.
2 tRNA’s fit into the ribosome at a time.
1st amino acid detaches from its tRNA.
The ribosome moves along 1 codon. 1st tRNA released from ribosome and goes back to cytoplasm. Another tRNA enters the ribosome.
The ribosome moves along 1 codon.
1st tRNA released from ribosome and goes back to cytoplasm. Another tRNA enters the ribosome.
Continues until a stop codon is reached, at this point the polypeptide will detach.
If the DNA sequence is TAC what is the mRNA / tRNA sequence
mRNA = AUG
tRNA = UAC
Anti-codon
Sequence of 3 on tRNA
Codon
Sequence of 3 on mRNA
What is a mutation?
Permanent change in the sequence of basses that make up a gene?
How do mutations arise?
Randomly due to errors during DNA replication. Can be sped up due to mutagenic agents / mutagens.
Eg. UV sunlight and X-rays (radiation)
Tar in smoke / carcinogens (chemicals)
Viruses (HPV) / bacteria (helicobacter) (infectious agents)
What can mutations be?
Neutral - no effect on fitness
Positive - advantageous, increases individuals fitness
Negative - deleterious, decreases individuals fitness
Silent mutation
Has no effect = due to degenerate coding as same amino acids is coded for therefore same protein made.
Nonsense mutation
Stop codon added in so protien can be non-functional when it’s incomplete. Premature stop codon, the severity of this depends on location of stop codon.
Missense mutation
Cahnges the amino acid coded fro so different protein produced.
What are deletion mutations?
Base is deleted = causes frameshift so every triplet/codon after is effected
What are addition mutations?
Base is added = causes frame shift so every triplet/codon after is effected.
Explain why errors in DNA replication can be far more damaging than errors in transcription?
During transcription = likely to be 1 off
During DNA replication = a whole cell has a mutation, any templates made from this cell will contain the mutation
Genome
Complete set of genes in a cell
Proteome
Full range of proteins a cell is able to make
mRNA structure
Short, single stranded polynucleotide chain.
Does not have complementary hydrogen bonds between base pairs
100s-1000s nucleotides in chain
1 polynulotide strand
Bases = A,U,G,C
tRNA structure
Clover shape
Has an amino acid attachment site
Has complementary hydrogen bonds between base pairs
1 polynucleotide strand
Less than 100 nucleotides in chain
Bases = A,U,G,C
ATP function
ATP transfers energy within cells by undergoing hydrolysis, which releases energy that can be used by the cell. This process involves the breaking of one of the phosphate bonds in ATP, which releases energy that can be used by the cell.
Releases energy for transcription and translation.
