Biology: DNA structure, profiling and genetic code

DNA structure

bucleic acid called deoxyribonucleic acid in the nucleus

double helix buildin block which contains a phosphate, deoxyribose sugar and a nitrogen base

4 diff nucleotide bases- adenine, guanine, thymine, cytosine

complomentray base pairs

2 matching base joined by hydrogen bonds

a purine bonds to a pyrimidine:

adenine bonds to thymine by 2 hydrogen bonds

guannine bonds to cytosine by 3 hydrogen bonds

DNA replication

making an exact copy of DNA , occurs late in the interphase of cell cycle

significance of DNA replication

ensures new cells formed will be genetically identical to parent cell

events of DNA replication

enzyme breaksdown hydrogen bonds between the base pairs to open the double helix

DNA nucleotides move to the nucleus from the cytoplasm and attach to exposed bases on each DNA parent strand by coplementary bad pairing

tow helices are formed from the original DNA molecule

DNA replication requires

ATP energy

DNA polymerase, catalyst to assemble DNA nucleotides

genetic code

codon is 3 bases in sequence, each codon codes for 1 amino acid
a gene is a unit of hereditory, with the genetic code to form a protein

experiment to isolate DNA from onion tissue

1. chop plant into small pecies to release cytoplasm

2. 2. add salt to clump up DNA2.

3. add detergant to break down cell membrane4.

4. warm at 60 degrees fpr 15 minutes iin water bath to denature enzymes that digest DNA

5. cool in ice water bath to slow down teh breakdown of DNA

6. blend for 3 seconds to break down cell wall

7. filter using coffee flter paper to collect filtrate containing DNA and protein

8. add protease an enzyyme wich digests protein

9. add freezer cold ethanol, DNA is insoluble in freezer cold ethanol, so DNA is brought out of solution and is seperated from filtrate

10. collect DNA ise glass rod to collect pure DNA as clear mesh

how to know if DNA is pure or not in experiment

white mesh is impure as protein present, clear mesh is pure

DNA profiiling

examine DNA for a band pattern for comparison

stages of preparing DNA profiling

1. cells are broken doen and DNA is extracted from biological sampleseg. blood / saliva

2. DNA is cut into fragments using restriction enzymes

3. fragments are seperated by size using gel elextrophoresis

4. band pattern is analysed and compared

gel electrophoresis

DNA fragments are added to a sugar based gel and an electric current is applied
small DNA fragments move faster through the gel seperating from the larger fragments of DNA

how is band pattern analysed

radioactive probes are added which combine with the DNA fragments and flouresce
photogenic copy is prepared and DNA fragments appear a dark bands

applications of DNA profiling

forensic science
medical

forensic science

scientific investigation of a crime scene using DNA profiles prepared in legal cases

medical use of DNA profiling

used to establish biological parents of a child

why do identical twins have the same DNA profiles

both have the same genotype
as both came from the same zygote