What are nucleic acids?
- DNA, RNA
- Monomers are nucleotides
Structure of nucleotide. [image]
Describe the structure of a nucleotide.
- Components joined by condensation reactions:
- Ester bond
- Pentose sugar
- Glycosidic bond
- Nitrogenous base
What is pentose sugar?
- A sugar w/ 5 carbon atoms
- Can either be ribose sugar in RNA or deoxyribose sugar in DNA
What is a polynucleotide?
- Many nucleotides joined together
- A repeating sugar-phosphate backbone from which organic bases project
- Bond between phosphate and sugar is phoD- bond
What are the 5 bases?
- Uracil (RNA)
A purine will only pair w/ a pyrimidine.
What is complementary base pairing?
- Hydrogen bonds between pairs of organic bases
- In DNA, pairing is between adenine-thymine, guanine-cytosine
- In RNA, pairing is between adenine-uracil, guanine-cytosine
What is the structure of a pyrimidine? 3 bases.
- The bases grouped into pyrimidines are:
- Have a single-ringed structure
- They are: thymine, uracil, cytosine
What is the structure of a purine? 2 bases.
- The bases grouped into purines are:
- Have a double-ringed structure
- They are: adenine, guanine
What are the features of DNA? Where found, strands, sugar, bases, functions.
- In the nucleus
- 2 nucleotide strands:
- -> twisted into double helix
- -> linked by H-bonds between bases
- -> run antiparallel with 3' and 5' ends
- Sugar-phosphate backbone with deoxyribose sugar
- Bases: G, C, T, A
- Function: passes genetic info from cell to cell + gen to gen
- 3.2 bil base pairs = infinite variety of base sequences, providing genetic diversity
How is the structure of DNA related to its function?
- Stable structure - passes from gen to gen w/out change, rarely mutates
- H-bonds - between strands, allows them to separate during replication/p. synthesis
- Large molecule - carries lots of genetic info
- Backbone - protects bases
- Base pairing - allows replication + mRNA
What is a double helix?
- Two strands of nucleotide
- Held together by hydrogen bonding
- Twisted around each other
What are the features of RNA? Where found, strands, sugar, bases
- Found throughout cell
- 1 strands -> can be folded into diff shapes
- Pentose sugar: ribose
- Bases: G, C, U, A
What does antiparallel strands in DNA mean?
The strands run in opposite directions.
What makes DNA a stable molecule?
- PhoD-backbone - protects bases inside helix from external forces
- Hydrogen bonds - link base pairs, forming bridges between strands
- -> 3 H-bonds are between C + G so the higher the proportion of C-G pairs, the more stable the DNA
Why is the nature of purine and pyrimidine bonding biologically important?
- Purines are larger - ensures that polynucleotide strands are equally spaced apart
- The structure of DNA remains exact and regular - vital since
- DNA carries the heredity material for an individual
- DNA can exist as a very long sequence of bases - to carry the large amount of genetic information
Why must DNA replication take place?
- For mitosis/protein synthesis
- So daughter cells have genetic info to produce enzymes/proteins they need
Why is DNA replication said to be semi-conservative?
When 2 new DNA are produced, one of the strands of each helix is from the original DNA and the other is new
The inheritance of DNA by daughter cells when a parent cell divides
Distinguish between the functions of DNA, mRNA and tRNA.
- DNA: carries genetic info inherited from parent DNA
- mRNA: carries genetic info from nucleus to ribosomes where polypeptides are synthesised
- tRNA: binds to amino acids + carries them to mRNA combines w/ ribosomes
What are genes?
- Sections of DNA
- Control characteristics by coding for proteins through sequences of bases
The position of a gene on a chromosome
Different version of a gene
How does a mutation occur in DNA?
- Bases swap
- Order of bases changes -> sequence of amino acids changes -> different primary structure -> diff tertiary structure -> changes characteristics
What are the requirements for semi-conservative replication? 5 requirements.
- The 4 types of nucleotide
- Both strands of DNA molecule - act as template for attachment of nucleotides
- Chemical energy
How does DNA replicate? 4 stages.
- Semi-conservative method
- DNA helicase breaks hydrogen bonds to separate strands
- Free nucleotides bind to complementary base pairs on template strands
- DNA polymerase joins nucleotides in condensation reactions, H-bonds and phoD-bonds form
- 2 identical DNA molecules are formed, each containing half the original DNA
How would DNA replication be affected if the enzyme polymerase was inhibited?
- Polymerase joins the 2 strands together
- If inhibited, DNA molecules would not form
- DNA replication would slow/stop