A1.2 nucleic acids Flashcards
PLEASE
In depth- function of DNA
Deoxyribonucleic acid:
- long-term storage for genetic information
- all cells in an organism share the same DNA, but each cell type only uses the relevant information
- composed of nucleotides formed by polymerisation
- sequences encode genes = code for amino acids = combine to form proteins = cell identification and function
- Made of Guanine, Cytosine, Thymine, Adenine
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Structure of nucleotides (DNA and RNA)
DNA and RNA are polymers of nucleotide
consist of:
- 5 carbon monosaccharide (pentose sugar - deoxyribose sugar for DNA and ribose for RNA)
- phosphate group attached to carbon atom (circle)
- nitrogenous base (A/T/C/G) attached to 1’ carbon (rectangle)
Describe the process and bonding btwn nucleotides to form the backbone (NOT btwn complementary base pairs)
sugar-phosphate bonds:
- a covalent phosphodiester bond forms btwn the phosphate group of a nucleotide and the sugar of the 2nd nucelotide = forms a “strong” backbone
- adding nucleotides along this chain is in the 5’ to 3’ direction
process:
- Linked by condensation reactions
- the phosphate group of a nucleotide attaches to the sugar of another nucleotide (at 3’ hydroxyl -OH group) = phosphodiester covalent bond formed = water released as a byproduct
Name the purines and pyrimidines and their structure
Purines (double-ring structure):
Adenine
Guanine
Pyrimidines (single-ring structure):
Cytosine
Uracil
Thymine
Describe the double helix structure of DNA
Double helix structure made of 2 antiparallel strands of DNA
- linked by hydrogen bonding btwn complementary base pairs
- the complementary base pairing and antiparallel arrangement help to stabilise the double-helix structure of the DNA
- 2 bonds btwn adenine and thymine
- 3 bonds btwn cytosine and guanine
Differences btwn DNA and RNA
Both are linear polymers consisting of a pentose sugar, phosphate, and bases
DNA:
- deoxyribose sugar (one less oxygen than ribose at 2’)
- Thymine
- double stranded
- shaped into double helix
- acts as permanent genetic code for cell
RNA:
- ribose sugar (one more oxygen than deoxyribose at 2’)
- Uracil
- single stranded
- variety of shapes
- no permanent genetic code, except for RNA in viruses
Draw ribose and deoxyribose
good job!
specific examples of nucleic acids (5) and their function
mRNA:
- mRNA synthesised from DNA template
- leave nucleus carrying genetic information necessary to produce proteins (in cells w nucleus)
tRNA (transfer RNA):
- when a specific protein is being synthesised, specific amino acids must be arranged in a specific order. tRNA transfers the correct amino acids to the chain of amino acids
rRNA (ribosomal RNA):
- involved in the formation of ribosomes
DNA
- store genetic information
ATP
- single-nucleotide nucleic acid
- type of chemical energy
Role of complementary base pairing
- stabilises double-helix structure of DNA
- maintains accuracy of DNA content during DNA replication
- crucial during DNA replication, where unzipped DNA strands serve as templates for the synthesis of new complementary strands, resulting in exact copies of the same molecule
- essential in gene expression, making sure of consistent protein production by accurately translating the genetic code [gene expression is regulated by turning genes on or off = complementary base pairing ensures that the same protein is produced each time a gene is expressed = maintain the characteristics of the cell and organism]
what allows DNA to be so diverse
incredible diversity of possible DNA sequences:
- DNA stores genetic information through sequences of nitrogenous bases, where every 3 bases forms a triple codon = 1 of 20 amino acids
- 4 different nucleotides = 64 combinations of triplets = leads to various to various lengths of DNA (range from millions to hundreds of millions of base pairs)
nearly limitless capacity of DNA to store genetic information:
- vast capacity of combinations of nitrogenous bases = vast capacity to store large amounts of data
What direction to DNA replication, transcription, and RNA translation follow and WHY?
Replication, transcription, and translation occur in the 5’ to 3’ direction
- reading direction is consistent to ensure the conservation of the DNA sequence during replication = ensures that the same protein is produced every time DNA is transcribed
- Enzymes involved in these processes:
1. (e.g. DNA polymerase) can only attach to the 3’ end (-OH) group = directional specificity of DNA these processes
2. other enzymes involved in DNA replication and translation can only add nucleotides in 5’ to 3’ direction - Less energy needed for these processes in 5’ to 3’ direction due to the orientation of the enzymes used in these processes
How does purine-pyrimidine bonds contribute to DNA stability
A purine always bonds with a pyrimidine:
A = T
C ≡ G
Because of this, there is always a constant distance btwn the antiparallel strands.
Describe the structure and purpose of the nucleosome
Structure:
- DNA (-ve) wrapped twice around a core of 8 histone proteins (+ve)
- An additional histone protein (H1) holds the nucleosome together
- linker DNA connects nucleosomes, creating a “string of beads” appearance
- a multitude of nucleotides then stack up in an organised pattern and begin coiling around other proteins in a very condensed shape = overall “packaged shape” is a chromosome
- access to DNA occurs when the coil unwinds and histones moved out of the way
Purpose:
- allows for efficient packaging of DNA in nucleus
- prevents DNA from damage
- regulate gene expression by controlling access to DNA for transcription and translation
Describe the experiment and evidence from the Hershey-Chase experiment for DNA as genetic material
Experiment
1. Viruses (T2 bacteriophage) were grown in 1 of 2 isotopic mediums in order to radioactively label a specific viral component
- Radioactive sulfur = radiolabelled proteins
- Radioactive phosphorus = radiolabelled DNA
2. The viruses were then allowed to infect a bacterium (E.coli)
3. Virus and bacteria separated by centrifugation
4. Larger bacteria formed the pellet, smaller bacteria remained in the supernatant
Evidence:
Bacteria pellet found to be radioactive only when infected by viruses infected with radioactive phosphorus (in DNA), and not radioactive when infected by viruses with radioactive sulfur (in proteins)
= DNA, not protein, is the genetic material as DNA was transferred to the bacteria.
Chargraffs rule
In any amount of DNA, the amt of Adenine = amt of Thymine, amt of cytosine = amt of guanine
