- Created by: sumayyahlorgat
- Created on: 09-06-18 21:23
Structure of RNA and DNA
- Deoxyribonucleic acid and ribonucleic acid
- double helix structure of DNA makes it immediately recognisable
- DNA carries genetic information
- Made up of three components:
- Pentose sugar (has five carbons)
- Phosphate group
- Nitrogen-containing organic bases (cytosine, thymine, uracil, adenine and guanine)
- They are all joined by a condensation reaction to form a single nucleotide (mononucleotide).
- Two mononucleotides may be joined by condensation reaction between the deoxyribose sugar of one mononucleotide and the phosphate group of another forming a phosphodiester bond
- Creates a dinucleotide.
- This continues to form long chains (polynucleotides)
- Ribonucleic acid (RNA) is a polymer made up of nucleotides.
- Single, short, polynucleotide chain which the pentose sugar is ribose and organic bases are A,T,C,U
- One type of RNA transfers genetic information from DNA to the ribosomes.
- Ribosomes are made up of proteins and another type of RNA.
- A third type of RNA is involved in protein synthesis
- 1953 = Watson and Crick worked on structure of DNA, following pioneering work by Rosalind Franklin on X-ray diffraction patterns of DNA
- Opened door for many major developments in biology over the next half-century
- In DNA pentose sugar is deoxyribose and the organic bases are A,T,C,G and is made up of two strands of nucleotides (polynucleotides).
- Each strand joined by hydrogen bonds between bases.
- The phosphate and deoxyribose wind around each other to form a double helix and form backbone of the DNA molecule
- DNA thought of to be a ladder, where phosphate and deoxyribose molecules alternate to form uprights and organic bases pair together to form rungs
- Bases on the two strands of DNA attach to each other by hydrogen bonds.
- Adenine joins with Thymine and Guanine joins with Cytosine, as a result of complementary pairing
- The concentration of A and T, G and C are always the same in DNA. However, the ratio of A and T to G and C varies from species to species
Stability of DNA
- Phosphodiester backbone protects the chemically reactive organic bases inside double helix
- Hydrogen bonds link organic base pairs forming bridges (rungs) between the phosphodiester uprights. 3 hydrogen bonds between C and G, higher proportion of C-G, more stable DNA molecule
- there are other forces between base pairs that hold the molecules together (base stacking)
Function of DNA
- DNA = hereditary material responsible for passing genetic information from cell to cell and generation to generation
- There are 3.2 billion base pairs in DNA of mammal cells. There is infinite variety of sequences and will provide genetic diversity.
- Function depends on sequence of base pairs
- Very stable structure from generation to generation with no changes as rarely mutates
- 2 separate strands joined by hydrogen bonds allows them to separate during replication and protein synthesis
- large so can carry lots of genetic information.
- By having base pairs with helical cylinder of deoxyribose-phosphate backbone the genetic information is protected from being corrupted by outside chemicals and physical forces
- Base pairs allow to replicate…