1. Nucleic Acids & Protein Synthesis
Chapter 10
Nucleic Acids & Protein Synthesis

2. DNA (Deoxyribonucleic acid)
The primary function of DNA in organisms is to store & transmit genetic information for the synthesis of proteins
Group of macromolecules called nucleic acids
Organic compound
Made up of repeating subunits called nucleotides
Consists of 2 long chains of nucleotides

3. Nucleotides Made up of three parts Sugar molecule called deoxyribose
Phosphate group
Nitrogen-containing base

4. Nitrogen-containing Bases
There are 4 different bases which are classified by their size:
Purines (larger in size having 2 carbon rings): Adenine (A) and Guanine (G)
Pyrimidines (smaller in size having 1 carbon ring): Thymine (T) and Cytosine (C)

5. History of DNA
Johann Friedrich Miescher (1869), a Swiss biochemist, isolated DNA
Because the molecules were acidic in nature and found in the nucleus Miescher called them nucleic acids
Rosalind Franklin and Maurice Wilkins developed X-ray photographs of DNA
The photographs indicated that DNA was a helix with a sugar-phosphate backbone

6. In 1953, James Watson (an American biologist) and Francis Crick (a British physicist) suggested a model of DNA
They proposed that DNA was composed of 2 long chains of nucleotides coiled around each other to form a spiral staircase called a Double Helix

7. Watson & Crick’s DNA Model
It can be compared to a twisted ladder
The sides of the ladder are made of alternating deoxyribose sugar & phosphate groups connected by covalent bonds
The rungs of the ladder are made of paired nitrogen-containing bases connected by weak hydrogen bonds

8. Pairs of bases are called Complementary Base Pairs
Erwin Chargoff, an American chemist, determined how the nitrogen-containing bases paired up
Pairs of bases are called Complementary Base Pairs
Base pairing rules
Cytosine bonds with Guanine
Thymine bonds with Adenine

9. Cytosine and Guanine form three hydrogen bonds
Thymine and Adenine form two hydrogen bonds

10. If one strand of DNA has a nitrogen base sequence of T-A-G-C-A-T, what would be the sequence of bases for the complementary strand?

11. The sequence of nitrogen-containing bases in DNA make up the codes for specific amino acids and amino acids make up proteins
In order for a new cell to function properly, it must contain a complete set of genetic instructions. Every new cell must receive an exact copy of the DNA.

12. Replication of DNA Replication is the process of copying DNA in a cell
During replication, the two nucleotide chains separate by unwinding and each chain serves as a template for a new nucleotide chain

13. Steps of Replication The separation of the two nucleotide chains
The point at which the chains separate is called the Replication Fork
Enzymes called Helicases move along the DNA molecule and break the weak hydrogen bonds between the complementary nitrogen-containing bases

14. New chains of DNA are assembled
Enzymes called DNA polymerases bind to the separated chains of DNA
As they move along the chain, complementary nucleotides are joined together to assemble new DNA

15. The DNA strands twist back together creating two identical DNA molecules (double helixes)
Each DNA molecule is made of one chain from the original DNA and one newly replicated chain

16. The replication process occurs at many points along the DNA molecule
This allows the copying of DNA to be completed faster
The cell is now ready to undergo cell division (Mitosis or Meiosis)

17. Accuracy and Repair DNA replication if highly accurate
1 error in every 10,000 paired nucleotides
A change in the nucleotide sequence called a Mutation can occur at any spot along the DNA molecule

18. Cells contain proofreading enzymes and repair processes that can detect and fix errors in the complementary base-pairing of DNA
Not all errors are detected or can be fixed by enzymes in the cell, therefore mutations can occur

19. Mutations can either be genetic or environmental in nature