1. DNA: The Code of Life

1. Core Content

Introduction

Revision of the structure of the cell with an emphasis on the ribosome, cytoplasm and the parts of the nucleus

Nucleic acids consist of nucleotides

Two types of nucleic acids: DNA and RNA

DNA: location, structure and functions

Location of DNA:

• Makes up the genes on chromosomes (nuclear DNA)

• Present in mitochondria (mitochondrial DNA)

Brief history of the discovery of the DNA molecule (Watson & Crick, Franklin & Wilkins)

Three components of a DNA nucleotide:

• Nitrogenous bases linked by weak hydrogen bonds:

- Four nitrogenous bases of DNA: adenine (A), thymine (T), cytosine (C), guanine (G)

- Pairing of bases in DNA occur as follows: A : T and G : C

• Sugar portion (deoxyribose in DNA)

• Phosphate portion

The natural shape of the DNA molecule is a double helix

Stick diagram of DNA molecule to illustrate its structure

Functions of DNA:

• Sections of DNA-forming genes carry hereditary information

• DNA contains coded information for protein synthesis

DNA replication

Process of DNA replication:

• When in the cell cycle it takes place

• Where in the cell it takes place

• How DNA replication takes place (names of enzymes not required)

• The significance of DNA replication

DNA profiling

Definition of DNA profile

Uses of DNA profiles

Interpretation of DNA profiles

RNA: location, structure and function

Location of RNA:

• mRNA is formed in the nucleus and functions on the ribosome

• tRNA is located in the cytoplasm

RNA plays a role in protein synthesis

Structure of RNA:

• A single-stranded molecule consisting of nucleotides

• Each nucleotide is made up of a sugar (ribose), phosphate and a nitrogen base

• Four nitrogenous bases of RNA: adenine (A), uracil (U), cytosine (C), guanine (G)

Stick diagram of mRNA and tRNA molecules to illustrate their structure

Protein synthesis

The involvement of DNA and RNA in protein synthesis:

• Transcription

- The double helix DNA unwinds.

- The double-stranded DNA unzips/weak hydrogen bonds break

- to form two separate strands.

- One strand is used as a template

- to form mRNA

- using free RNA nucleotides from the nucleoplasm.

- The mRNA is complementary to the DNA.

- mRNA now has the coded message for protein synthesis.

- mRNA moves from the nucleus to the cytoplasm and attaches to the ribosome.

• Translation

- Each tRNA carries a specific amino acid.

- When the anticodon on the tRNA

- matches the codon on the mRNA

- then tRNA brings the required amino acid to the ribosome. (Names of specific codons, anticodons and their amino acids are not to be memorised.)

- Amino acids become attached by peptide bonds

- to form the required protein.

Simple diagram to illustrate transcription and translation in protein synthesis

5. Informal Assessments