Basic Review of DNA

Biomolecules

These are the molecules that make up all living things

Carbohydrates Lipids Proteins-chains of amino acids Nucleic acids-chains of nucleotides

Elements

99% of any living thing is made up of just 4 elements.

Carbon-C Hydrogen-H Oxygen-O Nitrogen-N Phosphorus-P

Carbohydrates

Sugars such as glucose and starches The function is to store energy Made up of C,H,O

Lipids

Fats and oils The functions are energy storage,

insulation, protective cushion, and is the main component of cell membranes

Made up of C, H, H

Proteins

Structural proteins such as keratin, enzymes like amylase, most hormones like insulin

Functions include structure, growth, development, and metabolism

Made of C, H, O, N

Nucleic Acids

DNA and RNA Storing hereditary information, directing

the production of proteins. Made of C, H, O, N, P

How DNA is related to traitsDNA is protected in the nucleus of cells, it

has the directions for making proteinsDNA is transcribed into RNA which can go

out of the nucleus to the ribosomes (protein factories)

RNA is read by the ribosomes and translated into proteins

Proteins determine the traits you see.

DNA – RNA – PROTEIN – TRAIT Only 1% of the DNA leaves the nucleus of

the cell. That 1% is responsible for making DNA a

factor in Forensic testing

Structure of DNA

Made up of two chains of nucleotides Each nucleotide has 3 subunits

Deoxyribose sugar Phosphate ion One of four bases

Adenine Guanine Cytosine Thymine

The two chains of nucleotides come together to form a ladder.

The nitrogenous bases are the rungs of the ladder

Sugars and phosphates are the outsides of the ladder.

Adenine bonds with Thymine (Two bonds) Guanine bonds with Cytosine(Three bonds)

Recombinant DNA

When a genetic code is identified on a strand of DNA as having the instructions for a certain protein, biologists want to use this protein for research and drugs.

A recombinant DNA is a sequence of DNA that has been spliced at specific places to use the natural chemical producing abilities.

Restriction EnzymesThese are the enzymes that cut the

recombinant DNA. They are special “scissors” that cut a specific

strand of the DNA molecule when it recognizes the bases.

These pieces of DNA are introduced into bacterial or animal cells that reproduce the protein over and over.

Tandem Repeats This is a region of the chromosome that

has multiple copies of a core DNA sequence that repeat constantly.

More than 30% of the human genome is made up of these.

Seem to have no impact on genetic function or appearance.

Restriction Fragment Length Polymorphisms (RFLP) Different fragment lengths of base pairs

that result from cutting a DNA molecule with restriction enzymes.

All humans have the tandem repeats but the number of repeats differs greatly.

The first scientifically accepted protocol for DNA typing in the USA

Polymerase Chain Reaction PCR This is a technique to copy and multiply DNA

strands. Uses a DNA polymerase to synthesize a specific

region of DNA Uses temperature to break bonds and stimulate

replication. Better than RFLP, extremely sensitive. Has been

used to ID saliva on stamps, coke cans and envelopes.

Short Tandem Repeats STR Locations on the chromosome that contain

short sequence elements that repeat themselves within the DNA molecule.

Usually only 3-7 bases. Much shorter than RFLP procedure.

STRs can be found in bodies and stains that have been decomposed.

STR v/s Y-chromosome STR Amelogenin gene- gene for tooth pulp, is

shorter by 6 bases on X chromosome than the Y chromosome.

Y chromosome is male specific and always paired with the X

Very useful when more than one males is involved in assault.

Currently 20 different Y-STR markers have been id. A test kit is avail for 6 Y-STR .

This is only from the male so when looking at a DNA profile it will take out lots of overlapping info.on the profile Ex. A rape specimen: XX from female

XY from 1st suspect XY from 2nd suspect

Mitochondrial DNA Nuclear DNA is found only in nucleus and

contains 23 pairs of chromosomes Mitochondrial DNA- mtDNA- outside the

nucleus and is inherited only from the mother. The mitochondria are responsible for supplying

the energy of the cell. Each cell in our body has 100 to 1000 of

mitochondria.

Used in cases where the DNA is degraded such as charred remains and small quantities like the hair shaft

When a reference sample from a deceased or missing person, they can get mtDNA from any maternally related relative.However people with the same maternal linkage are indistinguishable.

This testing is more sensitive than nuclear DNA but is much more costly and time consuming.

The FBI has strict limits on the types of cases they will accept these samples from.

Combined DNA index System CODIS Allows crime labs to compare DNA types

recovered from crime scenes to DNA of convicted sex offenders and convicted criminals.

Uses 13 standard STRs

Collection procedures Biological evidence must be packaged in a

paper bag or well ventilated box, never in an airtight container.

Must be refrigerated or stored out of direct sunlight in a cool place, unless it is blood mixed with soil which must be frozen immediately

Must collect 7cc of whole blood for a reference or a buccal swab inside the mouth. To be kept refrigerated.

Contamination can occur if the collector sneezes or coughs during the collection .

Ways to prevent contamination Change gloves before each item Collect a control Pick up small items with forceps Each piece of evidence gets its own bag