Genes and DNAGenes and DNA

Chapter 6 page 144-154Chapter 6 page 144-154

DNADNA

• DNA-deoxyribonucleic acid. Is a molecule that is present in all living cells and that contains the information that determines the traits that a living thing inherits and needs to live

• Nucleotide found in a nucleic acid chain that contains a sugar, a phosphate group and a nitrogenous base

DNADNA

• 4 Nucleotides of DNA

• A. Adenine

• B. Thymine

• C. Cytosine

• D. Guanine

Chargaff’s rulesChargaff’s rules

• % of thymine will equal adenine for they always pair together

• % of cytosine will equal guanine

• This was found in the 1950’s by Erwin Chargaff

Franklin’s workFranklin’s work

• Was able to make images of DNA by x-ray diffraction thus by this process was able to say that DNA has a spiral shape.

Watson and CrickWatson and Crick

• After looking at chargaff’s work and Franklin’s work. They came to the conclusion that “DNA must look like a long, twisted ladder. This lead to the explanation on how DNA is copied and how it functions in the cell.

Copying DNACopying DNA

• Done by a process called replication

• Pairs of bases are complementary to each other

• Example the sequence CGAC will always bind with GCTG

Process of ReplicationProcess of Replication

• DNA is split down the middle where the bases meet. Thus the bases on each side is now used as a pattern for the new strand. So when this action of replication is done you will have one side of old DNA and one side of new DNA for each complementary strand.

When does replication occur?When does replication occur?

• Replication occurs every time a cell divides.

How DNA worksHow DNA works

• A. A typical skin cell has a diameter of about 0.0025 cm. The DNA is found in the nucleus.

• B. The DNA in the nucleus is a part of the material called chromatin.

• C. A single strand of chromatin is made up of a long strand of DNA that is coiled around proteins.

How DNA works (cont)How DNA works (cont)

• D. Each strand of DNA contains two halves that are connected in the middle and twisted in a double helix.

• E. When a cell is ready to divide, it packages the chromatin into chromatids. Two identical chromatids make up a chromosome that is ready to divide

How DNA works (cont)How DNA works (cont)

• E. Just before division, each human cell contains 46 chromosomes. These chromosomes contain two identical copies of all of the cell’s genetic material.

Making of ProteinMaking of Protein

• 1. A copy is made of one side of the DNA segment where a particular gene is located. Then it is transferred to the cytoplasm.

• 2. This mirrorlike copy of a DNA segment is called messenger RNA or mRNA.

Making of a proteinMaking of a protein

• 3. Each group of three bases on the mRNA segment codes for one amino acid

• 4. The mRNA segment is fed through the ribosome

• 5. Molecules of tRNA deliver amino acids from the cytoplasm to the ribosome.

Making of a proteinMaking of a protein

• 6. The amino acids are dropped off at the ribosome

• 7. The amino acids are joined to make a protein. Usually one protein is produced for each gene.

MutationsMutations

• Mutations are changes in the number, type or order of bases on a piece of DNA

• Types are deletion, insertion, substitution page 152 fig 3