DNA & GENES

DNA: the molecule of heredity DNA ultimately determines an organism’s traits. Within the structure of DNA is the complete instructions for manufacturing all the proteins for an organism.

DNA is a very long molecule. It can hold a lot of information. It is made out of repeating units called nucleotides.

Nucleotide Composed of 3 parts. Simple sugar phosphate group nitrogen base

Simple Sugar In DNA the simple sugar is ‘DEOXYRIBOSE’

Phosphate group Composed of one atom of phosphorus surrounded by 4 atoms of oxygen.

Nitrogen Base A carbon ring structure, containing some nitrogen. Four different nitrogen bases:

Adenine Symbol = A Classed as a Purine.

Guanine Symbol = G Classed as a Purine

Thymine Symbol = T Classed as a Pyrimidine

Cytosine Symbol = C Classed as a Pyrimidine

Typical Nucleotide

Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide.

In DNA the amount of Adenine is always equal to the amount of Thymine and the amount of Guanine is always equal to the amount of cytosine.

1953 James Watson and Francis Crick discovered what DNA looked like thus enabling scientists to understand how DNA stored information and worked.

Double Helix Watson and Crick discovered that: Adenine always bonded with Thymine. Guanine always bonded with Cytosine.

The two bonded bases are called complementary base pairs. This pairing of the bases causes the DNA to twist like a coiled spring (Helix).

Since DNA is composed of two strands and it has a helix shape it is referred to as a Double Helix.

All living things have DNA. The DNA is the same in every living thing. What makes living things different is the sequence of the DNA

The sequence of nucleotides forms the unique genetic information of an organism. A-T-T-G-G-C-T-A-C carries different information than: T-C-G-G-C-A-T-T-G

The more similar the DNA sequence between organisms the closer their evolutionary relationships.

DNA Replication DNA copies itself during the S phase of Interphase. Watson and Crick discovered that Adenine always pairs with Thymine and Guanine always pairs with Cytosine.

Step 1 DNA replication begins as an enzyme breaks the hydrogen bonds between nitrogen bases that hold the two strands together.

Step 2 Nucleotides that are floating free in the surrounding medium (inside the nucleus) bond to the single strands by base pairing.

Step 3 This process continues until the entire molecule has been replicated. The result are two identical strands of DNA.

ASSIGNMENT SA 11.1 problems 1-6