What is molecular biology?

The branch of biology that deals with the structure and function of molecules essential to life

What is biotechnology?

The use of biology to create useful technologies and products

Biotechnology in forensics

The use of techniques from molecular biology to analyze biological evidence -blood, saliva, skin cells-extract DNA profiles

Matthias Schleiden and Theodor Schwann

all organisms are made of cells and cells are the basic unit of life

Gregor Mendel deciphered

the genetic laws by conducting experiments on pea plants, and discovered the basic (segregation and assortment)

-dominant and recessive traits

Friedrich Miescher isolates

Nuclein from white blood cells

Walter Sutton and Theodor Boveri proposes that hereditary factors

are located on chromosomes which segregate during cell division

P.Levene, W.Jacobs, and others demonstrate

that RNA is composed of a sugar(ribose) plus four nitrogen bases, and that DNA contains a different sugar (deoxyribose) plus four bases

Frederick Griffith performed

information in the bacterium Streptococcus pneumoniae

-Heat killed bacteria transfer traits to live bacteria

-Evidence of a transforming principle

How did griffith perform his experiment?

Injected living S cells (in capsule) = mouse died

Inject living R cells (not in capsule) = mouse alive

Heat killed S cells (in capsule but non-pathogenic

Mixture of heat killed S cells and living R cells= mouse dies

Avery, MacLeod, MacCarty used a similar transformation test

injected DNase, RNase, lipase, protease, and other and determined that DNA is the transforming principle

Hershey and Chase shows that

DNA is transferred from bacteriophages to bacteria

Francis Crick lays out the

central dogma

DNA-> RNA-> Proteins

Two main types: of nucleic acids

DNA: carries genetic information in living organisms

RNA: plays various roles in coding, decoding, regulation, and expressino of genes

What do nucleotides contain?

- a nitrogenous base (adenine, cytosine, guanine, thymine, uracil)

- phosphate group

-linked to the 1C and 5C position of a (deoxy)ribose sugar

Which nitrogenous bases are purines and pyrimidines?

-Adenine and guanine are purines

-Cytosine, thymine, and uracil resemble pyrimidine

Bond that holds the nitrogenous base

glycosidic bond

The OH on the 3' carbon attacks

the phosphodiester bond and releases 2 phosphate groups

DNA double helix structure

Has sugar-phosphate backbones on the outside and the bases are aligned to the interior

When melting DNA,

The hydrogen bonds that hold the DNA strands together will weaken and break and causes denaturation

When annealing,

DNA is cooled to allow for the strands to come back together

Chromatin organization: the nucleosome unit

is repeated over and over and creates beads on a string

Te way in which a cell packages its chromatin

during interphase leads to two general forms

Euchromatin:

formed around sites of active genes

Heterochromatin

formed in regions of inactivity

Compare and contrast of Euchromatin and heterochromatin

When handling biological evidence, avoid contamination by not

-touching, sneezing or coughing over evidence

- always use clean gloves and tools

-change gloves between each otem you touch

To collct stains on a surface:

-wet stains: use sterile swabs or gauze

-dry stains: use distilled water ( for rehydration) and sterile swabs, or carefully scrape/cut the stained surface

You can locate invisible stains by:

Black light: excites proteins and metabolites in fluids, making them fluoresce

Alternate light sources: provide a range of wavelengths + filters to enhance faint stains

Biological evidence packaging:

-air dry thoroughly before packaging to prevent mold and DNA degradation

- Use proper packaging materials like paper bags or envelopes

- Clearly label for chain of custody by including case#, item #, date, intitals, signature

-Document every transfer to maintain chain of custody records

Biological evidence transport and storage

-Transport quickly and use secure, contamination-free evidence boxes

- Store dry and cold

-Short term: 4 C

Long term: -20 C or -80C

What is forensic Serology?

detection and identification of biological fluids using laboratory tests

Presumptive tests:

-Simple, quick, low-cost tests that detect the likely presence of body fluids

-use minimal material and preserve DNA integrity for further testing

Confirmatory tests:

- Provide definitive identification of a specific biological material

Designed to avoid cross-reaction with other fluids or species

Antigens

Molecules(often proteins or carbohydrates) on the surface of cells that can trigger an immune response

Antibodies:

-Immunoglobulins

- Proteins produced by B lymphocytes in response to specific antigens

- They bind to antigens, marking them for destruction or neutralization

Antigen-antibody reaction:

-immunological specificity

-essential for forensic serology tests

What are the limitations of blood antigen typing?

-Many people share blood type

- Antigens can degrade over time, especially in adverse environmental conditions

What are immunoassays?

Analytical tests that detect or measure substances( analytes) in a sample using highly specfic antigen-antibody reaction

Immunoassays can be aplied in

Drug screening, species identification, detection of body fluids, and hormone levels

What is the purpose of ELISA?

Uses an enzyme attached to an antibody to produce a measurable signal (color change) when the antigen-antibody reaction occurs

Modern role of serology:

-still crucial for initial screening, species identification, and preliminary drug testing before DNA or more advanced chemical analysis

The advert of DNA profiling (RFLP, STR) along with biotechnology (PCR, MPS):

-Revolutionized forensic individualization by providing far greater discriminatory power, even from degraded samples

VNTRs are

-short DNA sequences repeated consecutively at specific chromosomal locations

- ideal genetic markers for individual identification

- high polymorphic and distributed throughout the genome

-This variation creates different allele sizes

-Molecular scissors that cut DNA at specific sequences

Restriction Enzymes

What is a DNA probe?

-a short, single-stranded DNA fragment that binds to a complementary sequence in the target DNA

- must be labeled to make the target visible

- DNA samples must be denatured to single strands so the probe can hybridize to matching targets

What are the advantages of RFLP?

- high discriminating power: can individualize DNA to a very high degree, especially when multiple VNTR loci are analyzed.

- revolutionized forensic investigations by linking biological evidence directly to individuals

Limitations of RFLP:

-Time-consuming and labor-intensive, with multiple steps, and takes weeks for results

- requires large amounts of highly quality DNA (not suitable for trace samples)

- susceptible to degradation

- Cannot be easily automated

- paved the way for new technologies

(PCR) DNA template:

target DNA to be amplified

(PCR) Primers:

Short, synthetic single-stranded DNA sequences that are complementary to the ends of the target DNA region. They define what gets amplified

(PCR) DNA polymerase:

An enzyme that synthesizes new DNA strands ( Taq polymerase, which is heat-stable)

(PCR) Deoxyribonucleotides dNTPs:

the building blocks for new DNA strands (A,G,T,C)

(PCR) Buffer:

provides optimal conditions (pH, salts) for the reaction

For the visualization, nucleic acids are

stained using intercalating dyes that insert themselves and can be seen under UV or blue light, and the results are qualitative and presence/absence

Limitations of PCR:

-Contamination risk: are highly susceptible to contamination

- Inhibitor: substances in forensic samples can inhibit PCR reaction, leading to false negatives

- Prior sequence knowledge: requires knowledge of target DNA sequence to design primers

- Limited fragment length: PCR is best suited for amplifying relatively short DNA fragments

Short tandem repeats:

-The current gold standard

-has short repeats, which are ideal for PCR