DNA
DEOXYRIBONUCLEIC
ACID
Introduction
2.5.4 Introduction to Genetics.htm
 http://www.ornl.gov/sci/techresources/Human_Ge
nome/home.shtml
 http://www.youtube.com/watch?v=4HgFUvVyHYQ
 http://www.youtube.com/watch?v=QG7gkCrGD8k
Aidhm
What is DNA
 Deoxyribonucleic acid
 Hereditary material
 Carries and passes on genetic information
 http://learn.genetics.utah.edu/content/molecules/gene/
Basic Structure of DNA
• The 4 bases are:
1. Adenine (A)
2. Thymine (T)
3. Guanine (G)
4. Cytosine (C)
• Each pair as a link with
each other
(complimentary bases)
At
Giants
The
(AT)
Causeway (GC)
Basic Structure of DNA
• Double helix
• Two strands,
side by side.
(Like 2 halves of
a ladder)
• Strands are
linked by bases
So if one strand of DNA had the sequence TAGCAT. What
would the complimentary sequence be?
It would be ATCGTA
 The ladder is
twisted into a
spiral called a
double helix
Each base is
attached to a
sugar group
(deoxyribose)
which are linked
by phosphate
groups
Hydrogen bonds bond the base pairs.
Hydrogen bond- link
Parallel Strand
Base
Parallel Strand
Base
Building DNA
http://www.zerobio.com/drag_gr9/DNA/dna.htm
Genetic Code
 Genetic code: sequence of
bases in DNA that provide
instructions to make a protein
 Many amino acids make up a
protein
 Triplet/codon: 3 consecutive
base pairs that code for one
amino acid.
 Many amino acids make a
protein
DNA replication
 At the end of mitosis, each cell has a
single strand of chromosome
 To divide again, each cell must make an
exact copy of its DNA.
 A single strand of DNA must become
double stranded
 Replication means making a copy
DNA replication steps
1. Double helix
unwinds
2. Enzyme breaks
H bonds between
bases
DNA replication steps
3. Free floating
bases enter nucleus
from cytoplasm
4. Base pairing:
Incoming bases
attach to exposed
bases of each DNA
strand
DNA replication steps
5. This makes 2 exact
replicas of the original
DNA molecule
6. Each new piece
rewinds to make double
helix. Each double helix
is half new DNA, half
original DNA. They are
identical
DNA replication…why is it important
 When a zygote is growing by mitosis, the
chromosomes replicate and each of the new body
cells has an exact copy of the original chromosomes
Revision Check
What is the difference between meiosis and mitosis
Mitosis
Meiosis
The daughter cells have
___________
number of
the same
chromosomes as the parents
The daughter cells have
___________
number of
half the
chromosomes as the parents
The resulting nuclei are
identical
_________
The resulting nuclei are
different
_________
Two cells are formed
_______
Four
_______
cells are formed
Learning Check
Neighbours
What three things has your neighbour learnt today?
Can you….
Aidhm
DNA PROFILING
1980 - American researchers
discovered non-coding regions
of DNA
1984 - Professor Alec Jeffries
developed the process of DNA
profiling
1987 - First conviction based
on DNA evidence
Principle of DNA Profiling
All human chromosomes have sections of DNA with
no known functions
These sections have short base sequences
These sequences repeat over and over
They are inherited from parents
Their length and position are unique to each person
DNA PROFILING
DNA profiling: Examining DNA for a pattern
or band and comparing it to the DNA profile
of another person
STAGES INVOLVED
1. DNA extracted
2. DNA cut into
fragments of different
lengths using
restriction enzymes
3. Fragments separated
on basis of size using
gel electrophoresis
4. Pattern of fragments
analysed. Everyone has
a unique DNA profile
Did you know…..
1. DNA EXTRACTION
2. DNA cut into fragments using
Restriction Enzymes
Cuts between the G and A
in the sequence GAATTC
• Restriction enzymes cut DNA at specific
sequences.
• The distance between these sequences can be
different, so the DNA is cut up into different lengths
3. FRAGMENT
SEPARATION
Samples containing the
fragments are placed into
individual wells in a gel
using a pipette
This is known
as
electrophoresis
Gel
Electrophoresis
An electric current is
applied and fragments are
dragged along depending
on size. The smallest
move further and faster.
Uses of DNA profiling
1. Forensics: If blood
semen, saliva or hair
is left at the scene of a
crime, a DNA profile
can be created and
compared to a
suspect.
FORENSIC SCIENCE
Uses of DNA profiling
2. Medical:
Paternity and
maternity tests.
Childs DNA
profile can be
compared to the
parents.
FAMILY RELATIONSHIPS
Genetic Screening
 Genetic Screening is used to
establish the presence or absence
of certain genes.
 Defective genes cause disorders such as
1.
2.
Albinism: melanin pigment is not made
Sickle cell anaemia: abnormal haemoglobin
produced
Uses of Genetic Screening
 Adult screening: used to discover if adults carry a
defective gene
 Foetal screening: cells tested from placenta or
fluid around the foetus to test for genetic disorders.
Did you know….
Did you know….
Creating DNA Fingerprint simulation
http://www.pbs.org/wgbh/nova/sheppard/lab01.html
Learning check
Can you….
Aidhm
RNA
Ribonucleic Acid
DNA and RNA are both nucleic acids
Operates with DNA to make proteins
Has Uracil instead of Thymine
Adenine
Uracil
Guanine
Cytosine
Has the sugar ribose
RNA, Translation and Transcription
TRANSCRIBE & TRANSLATE A GENE:
First section on bases in RNA that are
complimentary to DNA
DNA
 Genes are sections of DNA found in the nucleus
 Genes control cells activities
 Genes have codes to produce proteins
 Many of these proteins are enzymes
 Proteins are long chains of amino acids
 Different amino acids assemble in a sequence to
make a protein. There are specific sequences for
different proteins
 DNA is found in the nucleus, mitochondria and
chloroplasts.
DNA and RNA
 DNA provides template for making RNA
 The sequence of bases in DNA determine the
sequence for RNA
 E.g.
DNA is
GGAATC
RNA is
CCUUAG
 3 base pairs = 1 amino acid
 RNA takes the genetic information from the DNA
in the nucleus to the ribosome where proteins are
made
Differences between DNA and RNA
DNA
RNA
Double strand
Single strand
Sugar is deoxyribose
Sugar is ribose
Has Thymine
Has Uracil
Found only in the
Found in nucleus and
nucleus, mitochondria,
cytoplasm
chloroplasts
Protein Synthesis
ORDINARY LEVEL
From Genes to Proteins
Changing DNA into proteins
involves a sequence of events
known as gene expression and
results in protein synthesis.
From Genes to Proteins
Gene expression
occurs in two steps:
1.
2.
Transcription: making
mRNA using DNA. Occurs in
the nucleus.
Translation: making a
protein using mRNA. Occurs
in ribosomes.
Steps
1. Separation: DNA strands separate in nucleus
Steps
2. Transcription: RNA bases move into nucleus,
attach to DNA (transcribed).
The RNA bases are complementary to DNA.
The RNA strand formed in this way is called
messenger RNA (mRNA).
Steps
3. mRNA detaches: moves out
of the nucleus and enters a
ribosome.
4. Each group of 3 bases (triple)
is the code for a particular
amino acid. The ribosome
translates the code and amino
acids are assembled in the
correct sequence for a specific
protein
Steps
4. Translation: Each group of 3
bases (triple) is the code for a
particular amino acid. The
ribosome translates the code and
amino acids are assembled in the
correct sequence for a specific
protein
Steps
5. Protein folding: The protein is folded into a 3D
shape. It is now functional.
Proteins
Proteins
 made up of one or more polypeptides
 which consists of a specific sequence of
amino acids
 A.a. linked by peptide bonds
 There are 20 types of amino acids
 The sequence of a.a. determines the structure
and function of the proteins.
Learning Check
Answers
Can you….
End
Higher Level
NUCLEIC ACID
STRUCTURE AND
PROTEIN SYNTHESIS
Aidhm
DNA
Detailed structure of DNA
 Nucleotide:
 Phosphate
(PO4)
 Sugar (deoxyribose – 5 carbon sugar)
 Nitrogen containing base
Form the
sides of
the DNA
strand
Nitrogen Bases
Purines
1. Adenine
2. Guanine
3. Thymine
Pyrimidines
4. Cytosine
Base Pairing
Guanine And Cytosine
Three Hydrogen Bonds
-
+
+
+
-
Base Pairing
Adenine And Thymine
Two Hydrogen Bonds
+ -
Adenine
-
+
Thymine
Base Pairing
Guanine And Thymine
+
+
The bonds between base pairs
A ----T: Two Hydrogen Bonds
G----C: Three Hydrogen Bonds
The Watson - Crick
Model Of DNA
The DNA ladder is
twisted into a double
helix
The outside strands are
deoxyribose and phosphate.
The base pairs are on the
inside
PROTEIN
SYNTHESIS
HIGHER LEVEL
Watch the clip and answer the
following questions
1. What unwinds and separates the
DNA
2. Name 3 types of RNA
3. Where does the assembled RNA
go after leaving the nucleus
4. What type of RNA attaches to
mRNA
Protein Synthesis
 http://www.youtube.com/watch?v=NJxobgkPEAo
Watch the clip and answer the
following questions
1. What unwinds and separates the
DNA
2. Name 3 types of RNA
3. Where does the assembled RNA
go after leaving the nucleus
4. What type of RNA attaches to
mRNA
Types of RNA
There are three types of RNA :
–mRNA (messenger RNA) -carries information
from DNA to ribosomes, transcribes DNA, leaves
nucleus to go to ribosomes
–tRNA (transfer RNA) - carries amino acids to
ribosomes for translation
–rRNA (ribosomal RNA) – holds mRNA in place
for translation. Is part of the structure of a ribosome
Remember: all produced in the nucleus!
Protein Synthesis - Steps
Stages:
1.
2.
3.
4.
5.
Enymes unwind DNA
Transcription
RNA processing
Translation
Folding
 Remember:
DNA  RNA  Protein
Step 1
 Enzymes in the
nucleus
 break
the bonds
between bases
 unwind the DNA
Step 2: Transcription
 RNA nucleotide
bases in the nucleus,
bond to exposed DNA
bases
 RNA polymerase
bonds the nucleotide
bases together to
make a string of
complimentary bases
to DNA.
Step 2: Transcription
 This string is now
called messenger
RNA (mRNA).
 RNA has
Start codon
Codons for amino
acids
End codon
This is a molecule of messenger RNA.
It was made in the nucleus by
transcription from a DNA molecule.
codon
A U G G G C U U AAA G C A G U G C A C G U U
mRNA molecule
Step 3: Translation
• mRNA moves out of nucleus and attaches to
a ribosome (where proteins are made)
• Ribosomes are large and small subunits.
Made up of rRNA + proteins
• Both units come together and help bind the
mRNA and tRNA.
A ribosome attaches to the mRNA
molecule.
ribosome
A U G G G C U U AAA G C A G U G C A C G U U
Amino acid
tRNA molecule
A transfer RNA molecule arrives.
It brings an amino acid to the first
three bases (codon) on the mRNA.
anticodon The three unpaired bases
(anticodon) on the tRNA link up
with the codon.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Another tRNA molecule comes into
place, bringing a second amino acid.
Its anticodon links up with the
second codon on the mRNA.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Another tRNA molecule
brings the next amino acid
into place.
A U G G G C U U AAA G C A G U G C A C G U U
A peptide bond joins the
second and third amino acids to
form a polypeptide chain.
A U G G G C U U AAA G C A G U G C A C G U U
The process continues.
The polypeptide chain gets longer.
This continues until a termination
(stop) codon is reached.
The polypeptide is then complete.
A U G G G C U U AAA G C A G U G C A C G U U
Step 3: Translation
• Amino acids are
attached to tRNA
• tRNA contains
anticodons
(triplet of bases).
Each amino acid
has a particular
anticodon.
Anticodon
Step 3: Translation
• tRNA attaches to
the complementary
codon on the
mRNA.
Step 3: Translation
• The 1st tRNA
molecule attaches
after the start
codon.
• Other tRNAs attach
to the
complementary
codons on mRNA,
bringing amino
acids.
• This allows certain amino acids to be lined up in
the correct sequence to make a particular protein.
• tRNAs continue to line up until the stop codon on
the mRNA is reached.
• The amino acids are detached from the tRNA.
End Product
 The end products of protein synthesis is a
primary structure of a protein.
 A sequence of amino acid bonded together by
peptide bonds.
aa2
aa1
aa3
aa4
aa5
aa199
aa200
start
codon
mRNA
A U G G G C U C C A U C G G C G C A U A A
codon 1
protein methionine
codon 2
codon 3
glycine
serine
codon 4
isoleucine
codon 5
codon 6
glycine
alanine
codon 7
stop
codon
Primary structure of a protein
aa1
aa2
aa3
peptide bonds
aa4
aa5
aa6
PROTEIN
SYNTHESIS
 http://www.youtube.com/watch?v=bVk0twJYL6Y&f
eature=related
Learning check
Can you….