DNA & RNA

Genes and DNA

• Chromosomes are composed mostly of DNA• DNA molecule is made up of four nitrogen bases:

– Adenine (A)– Thymine (T)– Guanine (G)– Cytosine (C)

A gene is a section of a DNA molecule that contains the information to code for one specific protein.

A single gene on a chromosome may contain several hundred to million or more bases.

Order of the Bases

• A gene contains the code that determines the structure of a protein.

• The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced.

• Proteins are long-chain molecules of individual amino acids.

How cells make proteins

• The production of proteins is called protein synthesis.

• During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.

• This process takes place in the ribosomes.

• Since the chromosomes are found inside the nucleus, so a messenger is needed to take the DNA information out of the nucleus.

The role of RNA

• A “messenger” must carry the genetic code from the DNA inside the nucleus into the cytoplasm.

• RNA is this messenger so is also know as RNA messenger RNA or mRNA.

• RNA and DNA have similarities but also many differences such:– RNA only contains one strand as oppose to DNA

which has two strands ( double helix)– RNA and DNA have different nitrogen bases, RNA

has uracil instead of thymine

Types of RNA

• mRNA: copies the coded message from DNA and carries the message to the ribosome.

• tRNA or transfer RNA: carries amino acids to the ribosome and adds them to the growing protein.

Translating the Code

1. DNA molecule “unzip” between its base pairs, one DNA strand directs the production of a mRNA strand

2. RNA bases pair with DNA bases.

3. mRNA leaves the nucleus and goe to the cytoplasm

4. mRNA attaches to the ribosome and provides it with the code to the protein that will be form.

5. tRNA attaches to mRNA, tRNA carries specific amino acids to the ribosome.

6. The message is read by matching the bases with other bases and creating 3 letter codes.

7. The protein grows as each amino acid is attached.

8. The protein stops growing when the ribosome finds a 3 letter code with the message Stop.

9. The protein is then release by the ribosome.

Mutations:

• Mutations can cause a cell to produce an incorrect protein during protein synthesis.

• As a result, organism’s trait, or phenotype, may be different from what it normally would have been.