human bio

DNA- deoxyribonucleic acid

• contains genetic information about organisms within nucleus of our cells. capable of self- replication

Purpose of DNA

for organism survive, develop and reproduce → production of proteins, regulation, metabolism + reproduction of cell

Structure of DNA

shaped like double-stranded helix (like a corkscrew) 

Nucleotide: (building blocks)

make up backbone of DNA

DNA model (ladder)

 Twisted ladder

• label sugar, hydrogen, phosphate, nitrogenous

• sides= sugar phosphate backbone

• Rung: bases: AT, GC

4 different Nitrogenous base

•   Thymine (T): 

• Adenine (A):

• Cytosine (C)

• Guanine (G):

Within a DNA chain 

- Adenine - Thymine (u) : AT

Guanine - Cytosine: GC

Genes + chromosomes 

 Each cell contains approx. 1.8m of DNA 

• Coils around histones (proteins) to allow it to condense 

• • Chromosomes only present when cell replication is occurring. 

• • DNA is usually found as chromatin 

• • 23 pairs or 46 chromosomes in each cell

Function of DNA genes

1. chromosome consists of segments of DNA (genes)

2. Genes contain the instructions for the construction of a particular protein, or RNA.

3. estimated about 20,000–25,000 genes in human genome ( 3 b base pairs).

Purpose of proteins: 

• important role in many bodily functions 

• Humans use 1 billion proteins every day to function 

• • Build and repair tissues 

• • Enzymes to break down substances 

• • Hemoglobin in blood carries oxygen 

• • Hormones regulate development

Protein synthesis transcription: 

• Happens in the nucleus of the cell 

• DNA → messenger RNA (mRNA) 

• An enzyme binds to the DNA at the gene being copied 

• The DNA strand unwinds 

• One side of the strand is read 

• A complementary copy of the strand is made - mRNA

• The only difference is Uracil (U) replaces Thymine (T) 

• The mRNA moves away from the DNA and the DNA strand is zipped back up

Translation: 

• mRNA moves into the cytoplasm and binds to a ribosome 

• The ribosome reads the mRNA one codon at a time (3 bases) 

• Each codon is code for a specific amino acid 

• The amino acids are joined together to form a protein

DNA  mutations:

• changes in nucleotide sequence of DNA

• > somatic cells/mutation

       - in normal body cells

       - not passed on to offspring

Mutations

hange in nucleotide sequence of DNA

Somatic mutation:

not passed on + occurs in body cells

Gremlin mutation:

  - in gametes (sex cells)

  - can be passed on, cause inherited disease 

Helpful or harmful?

• happen regularly

• Usually neutral

• Caused by mutagens (chemicals, UV) 

• Many mutations healed by enzymes

• Some are benefits 

Point mutation: (one base changes)

Change in ONE nucleotide

point mutation:

• Intersection: extra base added

• Deletion: base is removed

• Substitution: one base is swapped (A->G)

Sickle cell disease

 result of one nucleotide substation (in haemoglobin gene) 

Frame shift mutation

• inserting or deleting one or more nucleotides

• Changes reading frame like changing a sentence

• Proteins built incorrectly

DNA fingerprinting

• tracing ancestry

• Forensic science e.g 

• Identification of carriers of hereditary disease

• Early detection of inherited disease e.g certain cancers

• Risk of passing on disease

• Parentage e.g who did is for child

• Research e.g species of fossils

• forensics: 

• all bands are the same= same person

*parentage:

• about half of bands from each parent

Gel electrophoresis: 1984 profiling techniques

• DNA cut by enzymes then placed on semi solid gel bed

• Electric current passed through plate

• DNA negatively charged- moves towards positive electrode

• Smaller piece's= faster + further, lager pieces= slower

PRC: polymerase chain reaction

• fast + inexpensive technique used to ‘amplify’ (copy) small segments of DNA 

• Need a significant amount of DNA to perform molecular and genetic analyses

• Studies of isolated DNA are nearly impossible without PCR amplification 

• Once amplified the DNA can be used in many procedures including DNA fingerprinting and diagnosis of genetic disorders

steps of PCR

1. Denaturing - 94-95ºC: Heat DNA to break hydrogen bonds between bases – 2 single strands 

2. Annealing – 50-56ºC: Primers bind to complementary strand on target sequence 

3. Extending – 72ºC: Starting at the primer, the DNA polymerase reads the DNA code and builds a complementary strand of DNA – each strand can then be used to create 2 new copies and so on 

4. Can be repeated as many as 30-40 times leading to the creation of more than 1 billion exact copies of the original strand

Ethical issues:

Do benefits outweigh risks?

What will happen if info is stolen?

Cases (parentage) where DNA was obtained without consent