Heredity: Is the passing on of features from parents to offspring by means of genes.

Gene: Is a section of DNA that causes the production of a protein.

Gene expression: Is the way in which the genetic information in a gene is decoded in the cell and used to make protein.

Characteristics: Are traits or features that are inherited genetically.

Structure of DNA

DNA stands for deoxyribonucleic acid. DNA is a double stranded molecule made up of elongated chains of sub-units called nucleotides. DNA contains four chemicals called base pairs which are:

-Adenine (A)

-Thymine (T)

-Guanine (G)

-Cytosine (C)

A joins with T (2 hydrogen bonds) and G joins with C (3 hydrogen bonds).

Each nucleotide is made up of a phosphate, a sugar and a base.

DNA Replication

-Different base pairs join together A-T and G-C

-The Double helix unwinds

-An Enzyme breaks the bonds between the base pairs.

-The two strands of the double helix separate

-The new copies of bases attach to the exposed complementary bases.

-The DNA molecule acts as mould or template for the new DNA that is formed.

-The new double strand rewinds to form a double helix.

DNA profiling

-The DNA is released from the cells

-DNA is cut into fragments of different length.

-Fragments are separated according size.

Patterns produced by the fragments are compared.

Examples of DNA profiling are forensic scientists and Paternity Disputes.

RNA Structure

RNA stands for ribonucleic acid. RNA is singled stranded. RNA consists of four chemical bases which are

-Adenine (A)

-Uracil (U)

-Guanine (G)

-Cytosine (C)

A joins with U instead of T and G joins with C

Difference between DNA and RNA

-DNA contains the sugar deoxyribose and RNA contains the sugar Ribose

-DNA contains the bases A, t, G and C and RNA contains the base A, U, G and C

-DNA is a double helix strand and RNA is singled stranded.

Protein synthesis:


-The DNA unwinds and the two strands separate. Enzymes are involved in this process.

-RNA bases in the cytoplasm moves across the nuclear membrane.

-RNA bases will match up with the complementary bases.

-RNA enzyme polymerase causes RNA bases to join together.


-mRNA moves from the nucleus to the cytoplasm.

-Ribosomes are made up of ribosomal RNA and protein

-mRNA strands form weak bonds

-In a ribosome will be the site of protein synthesis

-tRNA molecules attracted to the mRNA

-tRNA is complementary to mRNA

-A start codon begins the process of translation.

– tRNA’s attach to the mRNA two at a time. Carrying their precise amino acids to the ribosome.

– tRNA molecules leave the ribosome leaving their amino acids.

-tRNA molecules continue to bind with the mRNA until a stop codon is reached.

-The amino acid sequence of the new protein is now complete.