Download DNA - thatscienceguy

CATALYST


Read the case study on pg 158
In your notebook, answer the following
questions in complete sentences:
–
–
–
1
How was DNA fingerprinting used in this case?
Only half of Andrew’s DNA fingerprint is the same
as his Christiana’s DNA. Is that enough to prove,
beyond a doubt, that Andrew is her son?
Why did they run a DNA fingerprint on
Christiana’s other children?
Chapter 7 DNA Fingerprinting
By the end of this chapter you will be able to:
 explain how crime scene evidence is
collected and processed to obtain DNA
 describe how radioactive probes are used in DNA
fingerprinting
 explain how DNA evidence is compared for
matching
 explain how to use DNA fingerprinting to identify
DNA from a parent, child, other relative, or a nonrelated individual
All Rights Reserved South-Western / Cengage Learning © 2009
2
Introduction and History of
Biological Evidence in Forensics
 DNA fingerprinting, also known as DNA
profiling, is used in criminal or legal cases with
a high degree of accuracy.
 Biological evidence such as blood, saliva,
urine, semen, and hair is examined for the
presence of inherited traits.
3
Introduction and History of
Biological Evidence in Forensics
 DNA is the blueprint of life and contains the
genetic material of a cell.
 DNA holds all the information and instructions
needed for a cell to make proteins and replicate
 Genetic information is stored in molecules of
DNA making up structures called
chromosomes
4
–
Found in the nucleus of cells in the human body.
Introduction and History of
Biological Evidence in Forensics

Rosalind Franklin
–
–
1950’s English Chemist
Used X-ray crystallography to
create image of DNA
 Looked
like rungs, like those on a
ladder between two strands that are
side by side
 ‘X’ shape suggested a spiral or helical
molecule
5
Introduction and History of
Biological Evidence in Forensics

Watson & Crick
–
6
1953 used
Franklin’s picture to
make an accurate
3-D model of DNA
DNA Structure
7

DNA = deoxyribonucleic acid

Polymer consisting of
thousands of smaller, repeating
units called nucleotides
DNA Nucleotides

A DNA nucleotide is composed of three
parts:
1.
8
Phosphate group: made of oxygen,
hydrogen, and phosphorous
DNA Nucleotides
2.
9
Deoxyribose: 5-carbon sugar made up
of carbon, hydrogen, and oxygen.
DNA Nucleotides
3.
Nitrogenous base:
made up of carbon,
oxygen, hydrogen, and
nitrogen
3. There are 4 types:
purines
pyrimidines
10
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
DNA Structure

11
DNA is made up of two strands of nucleotides
that form a structure that looks like a twisted
ladder which we call a double helix.
DNA Structure

Double helix
–
–
Backbone (sides of
ladder): polymer with
alternating sugarphosphate sequence
Connected by the
nitrogenous bases
held together by
hydrogen bonds
H Bond
phosphate
sugar
12
13
Base Pairings

Chargaff’s rule
–
–
–
14
Erwin Chargaff (1950)
Amount of adenine (A) equals the amount of
thymine (T)
Amount of guanine (G) equals the amount of
cytosine (C)
Base Pairings

Complimentary Base Pairings: every
base pair consists of one purine (A or G)
and one pyrimidine (T or C)
–
–
15
Adenine (A) always pairs with thymine (T)
forming 2 hydrogen bonds  A-T
Guanine (G) always pairs with cytosine (C)
forming 3 hydrogen bonds  G-C
DNA Structure

When the base pairs of the DNA strands
form a double helix, the strands are
considered to be complimentary
–
16
if the bases in a section of one strand is
CGTCTA, then the order of bases in the
complementary section of DNA in the other strand
is GCAGAT
CGTCTA
GCAGAT
DNA Structure

DNA makes up
structures known as
chromosomes
–
–
17
DNA coils into
chromosomes around
proteins
Chromosomes are
found in a cell’s
nucleus
Human DNA

There are 23 pairs (total of 46) of
chromosomes in the nucleus of most
human cells (except sperm and egg cells)
–
One chromosome in each pair is inherited
from the mother and the other is inherited from
the father
 50%
18
of a person’s DNA come from each parent
Human DNA

Nuclear DNA: found in the chromosomes
–
–

Mitochondrial DNA: found in the mitochondria
–
–
19
Virtually identical in all cells of the human body
DNA fingerprints are derived from nuclear DNA
Only inherited from the mother
Can be used to identify a person’s mother
Genes & Alleles

Each chromosome contains many
genes
–
Genes: DNA sequences that have
instructions that determine our inherited
characteristics of traits
 Genes
determine our characteristics (i.e. blue
eyes, brown hair,
 Used to produce proteins or RNA (ribonucleic
acid)
20
Genes & Alleles

We can have two versions of each
gene
–
–
Allele: one of the alternative forms of the
genes
One allele comes from the mother and the
other comes from the father.
 Example:
–
21
One allele codes for normal hemoglobin while the
other codes for abnormal hemoglobin
DNA

Encoded DNA (exons): DNA used to make
up proteins and other molecules

Unencoded DNA (introns): DNA that does
not produce proteins or RNA molecules
–
22
Important in gene splicing
DNA

The human genome is the total amount of DNA
in a cell (both nuclear and mitochondrial)


23
There are 3 billion base pairs and 23,688 encoded genes in
the human genome
– That is less than 1.5% of the DNA in the genome (more
than 98.5% is non-coding)
If you took out all of the DNA in all of your cells
and stretched the strands end to end you could
reach the moon…
– 6000 times!