Chapter 15: DNA and RNA

Heredity (Genetic Inheritance)

Passing on of features from parents to offspring by means of genes.

Genes

Sections of DNA that causes the production of a specific protein.

Characteristics

Controlled by gene, arise from the interaction of heredity and environment.

e.g. hair colour, eye colour, height

Gene Expression

The way genes are decoded in the cell and used to make a protein.

Chromosomes

Made of 60% protein and 40% DNA.

Genes are located along the chromosome.

Contains large sections that do not contain genes (Non-Coding DNA), found within genes and between genes.

Locus

Location of gene on a chromosome.

DNA

DNA consists of double helix structure and is twisted into a spiral.

Made up of units called nucleotides.

Nucelotides

Phosphate + 5 Carbon Sugar + Nitrogen Containing Base

Polynucleotides

Chains of nucleotides

DNA Structure was discovered by James Watson and Francis Crick

Purines and Pyrimidines

Purines: double ringed molecules

• Adenine, Guanine

Pyrimidines: single ringed structures

• Thymine, Cytosine.

Adenine and Thymine form 2 weak hydrogen bonds

Guanine and Cytosine form 3 hydrogen bonds

DNA Replication

1. Double helix unwinds.

2. DNA helicase breaks hydrogen bonds between base pairs.

3. Free floating bases in the cytoplasm enter the nucleus.

4. Incoming bases attach to their complementary bases (2 exact replicas of the orignal DNA molecule)

5. Each new DNA rewinds to form a double helix.

Each new DNA molecule is identical to the original and eachother, and contains half new and half old DNA (semi-conservative).

DNA Profiling

1. DNA Extraction
   DNA is released from cells

2. Restriction
   Isolated DNA is cut using restriction enzymes.
   Each restriction enzyme is specific to a base sequence.

3. Separation
   DNA is separated according to size by a process called Gel Electrophoresis.
   DNA is negatively charged and moves towards the positive end.
   The smallest lightest pieces move the furthest. Larger fragments move the least.
   This leaves distinct bands in the gel. (radioactive mateial added to make image).

4. Patterns are compared
   Every DNA profile is unique.

Application of DNA Profiling

• Crime
  Blood, hair, seme or salive left at a crime scene could incriminate or eliminate a suspect.

• Medical
  Paternity and maternity cases can be resolved. Blood sample is taken and DNA profiles examined.

Genetic Engineering

• Isolation

• Cutting

• Insertion

• Transformation

• Expression

Isolation

• DNA released from donor cell.

• Gene of interest isolated.

• Bacterium DNA also released.

• Plasmid isolated.

Restriction

• Restriction enzymes cut DNA at restriction sites.

• Same enzyme cuts donor DNA and bacterial DNA.

Insertion and Ligation

• Isolated gene is placed into the vector and joins it.

• DNA ligase is placed into the vector and joins it.

• DNA ligase acts like glue and sticks pieces of DNA together.

• Ligation results in recombinant DNA.

• New DNA = hybrid.

Transformation

• Recombinant DNA is introduced to bacterial cell.

• If bacterial cell uptakes recombinant DNA it is transformed.

Cloning

• Bacterial cell replicates by binary fission.

• Each new cell is identical to the parent.

Expression

• Organism with recombinant DNA produces desired protein

• When protein is produced in large amoounts it is isolated and purified.

Genetic Screening

Testing DNA for the presence or absence of a specific gene or altered gene.

Adult Screening

Can be used to identify if an adult is carrying a defective gene. This gene may effect their own health or their childrens health.

e.g. Cystic Fibrosis, Cancer, Haemochromatosis.

Embryonic/Foetal Screening

Cells taken from embryo/placenta/fluid around baby and tested for genetic defects.

RNA

Protein Synthesis

DNA is a template for RNA, RNA makes proteins.

1. Initiation
   DNA unwinds in the nucleus and the bonds between the bases break down (helicase)
   

2. Transcription
   RNA nucelotides outside the nucleus move across the nuclear membrane.
   These bases line up with the complementary DNA strand.
   RNA polymerase joins the bases to make messenger RNA (mRNa).
   

3. Translation
   mRNA moves into cytoplasm and attaches to ribosomes.
   (ribosomes are made of ribosomal RNA (rRNA) and protein)
   (Cytoplasm contains transfer RNA (tRNA))
   tRNA are attached to mRNA.
   Each tRNA has an anticodon that is complementary to codon on mRNA.
   This ensures amino acidds are in the correct sequence to form a protein.
   tRNA moves through ribosome until a stop codon is reached.
   Amino acids that detach from tRNA bond together (peptide bonds).
   Protein folds into its shape.
   

DNA and RNA work in sets of 3 called codon. Each codon makes one amino acid.

Every gene has:

Start Codon - Beginning of gene, not involved in protein production.

End Codon - End of gene, not involved in protein production.

Series of codons inbetween - specify a protein.