3: Nucleic acids Flashcards
What are the two types of nucleic acids?
DNA and RNA - both have roles in storage and transfer of genetic information and synthesis of polypeptides
What are nucleic acids?
Large polymers formed from many nucleotides (monomers) linked together in a chain. Contain carbon, hydrogen, oxygen, nitrogen and phosphorus
What is a nucleotide made up of?
- Pentose monosaccharide (sugar)
- Phosphate group (acid and negatively charged)
- Nitrogenous base
How are polynucleotides formed?
Nucleotides are linked together by condensation reactions to form a polymer (polynucleotide). Phosphate group at the 5th carbon of the pentose sugar of one nucleotide forms a covalent bond with the hydroxyl group at the 3rd carbon of the pentose sugar of an adjacent nucleotide. Bonds formed are called phosphodiester. Forms a long, strong sugar-phosphate ‘backbone’ with a base attached to each sugar
How are phosphodiester bonds broken?
Hydrolysis (reverse of condensation), releases the individual nucleotides
What is DNA?
Deoxyribonucleic acid
- Sugar is deoxyribose (one fewer oxygen atoms than ribose)
- A nucleotide (one of four possible bases)
What are the four different DNA nucleotides?
Adenine, thymine, cytosine and guanine
What are pyrimidines? Which bases are pyrimidines?
The smaller bases, which contain single carbon ring structures. Thymine and cytosine
What are purines? Which bases are purines?
The larger bases, which contain double carbon ring structures. Adenine and guanine
What makes up DNA molecules?
Two strands of polynucleotides coiled into a helix (DNA double helix)
What holds the two strands of the double helix together?
Hydrogen bonds between bases
Why are the strands of polynucleotides said to be antiparallel?
Each strand has a phosphate group (5’) at one end and a hydroxyl group (3’) at the other end. The two parallel strands are arranged so that they run in opposite directions, therefore antiparallel
How are bases paired (complementary base pairing)?
Adenine and thymine are both able to form two hydrogen bonds so always join with each other. Cytosine and guanine form three hydrogen bonds and so only bind to each other
What does complementary base pairing mean?
DNA always has equal amounts of adenine and thymine, and equal amounts of cytosine and guanine
What is RNA and what is its role?
Ribonucleic acid. Transfers genetic information from DNA to proteins that make up the enzymes and tissues of the body
