Summary Life Sciences (Biology) - Nucleic acids

NUCLEIC ACIDS:


DEOXYRIBONUCLEIC ACID (DNA)


CHROMATIN NETWORK:
 Network condenses to reveal individual chromosomes.
 Long DNA strands wind around histones.
 Histones = protein that prevents DNA from getting tangled.




STRUCTURE OF DNA:
 Forms a double helix shape
 Made up of subunits = nucleotides
 Has Adenine, thymine, guanine, cytosine
 Complimentary base paring means the order of the of the bases in the copy
strand is determined by the order of the bases in the template strand
 Bases arranged in pairs of three called codons
 A gene = a section of DNA that consists of a unique sequence to form a protein
 DNA strand -> genes -> protein -> trait


NUCLEOTIDES:
 Monomers of DNA = nucleotides
 Each nucleotide contains
- Pentose sugar ( DNA – deoxyribose and RNA – ribose )
- Phosphate group
- Nitrogen containing base
 Sugar + phosphate group = back bone of DNA
 Nitrogen bases = rungs of DNA
 Two types of bases
1. Pyrimidines:
- Consist of Cytosine, thymine and uracil
- Smaller bases ( only one circle)
- 3 weak hydrogen bonds
2. Purines :
- consists of adenine and guanine
- larger bases ( two circles)
- 2 weak hydrogen bonds

, DNA REPLICATION:
 Takes place during interphase of mitosis
 Important to transmit identical DNA to each new cell.


Step 1:
- Enzyme polymerase breaks up weak H bonds between N-Bases
- Helix uncoils
- Original strand provides code for the complimentary strand.



Step 2:
- Free nucleotides from nucleoplasm bond to complimentary bases ( A+T and
G+C)
- Deoxyribose sugar bonds with phosphates to form back bone



Step 3:
- Replication occurs along entire length of DNA
- DNA recoils into double helix
- One new DNA molecule = old strand + new strand