DNA and RNA
Protein - Recall
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DNA contains the code to make all
the proteins in your cells!
Function of Protein in humans?
Growth, Repair, Enzymes, Hormones, etc.
Function of proteins in the cell?
They control the cell (by enzymes mainly)
What are proteins made of?
Amino Acids
What is important about these amino acids?
That they are in a very specific sequence
DNA and RNA
Learning intentions:
• Understand DNA structure including
complementary base pairing and genetic
code
• Describe the process of DNA replication
2015 Q7
DNA is a
double helix
Structure of DNA
DNA – Deoxyribonucleic Acid
https://www.youtube.com/watch?v=7
Hk9jct2ozY&ab_channel=WEHImovies
Structure of DNA
Four different nitrogen containing bases in DNA
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
DNA is composed of Nucleotides
• A nucleotide is made up
of a phosphate, sugar
and nitrogen base
• The phosphate and
sugar make up the
backbone of DNA
• There are four different
types of nucleotide
Many Nucleotides joined together is a
polynucleotides
DNA Structure
• Structure:
1. Phosphate
2. Deoxyribose sugar (carbohydrate)
3. Nitrogenous base.
• BASES:
– Purines
• Adenine (A)
• Guanine (G)
– Pyrimidines
• Thymine (T)
• Cytosine (C)
• A Purine always matches up
with a Pyrimidine!
• Purines – 2Hydrogen Bonds
• Pyrimidines – 3 Hydrogen Bonds
2012 Q10 a
i. Purine, Pyrimidine
ii. Adenine - Thymine,
Guanine - Cytosine
Learning check
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Name the 4 nitrogenous bases of DNA
Name the purine bases
Name the pyrimidine bases
What are nitrogenous bases connected by?
Explain the complementary base pair rule
The Genetic Code
A gene carries different codes to
control the formation of the
different amino acids
Triplet (codon) - A sequence of three
bases possessing a code for a
particular amino-acid
DNA Replication and Profiling
Learning intentions:
● Describe the process of DNA replication
● Describe the process of DNA profiling
EQ - Explain the genetic code (9 marks)
A sequence of ……….is a triplet
A sequence of triplets determines ……….
A sequence of ………..determines the ………..made.
DNA Replication
https://www.youtube.com/watch?v=7Hk9jct2ozY
2010 Q10 a.
i. original strand is unzipped and unwound
ii. new strand is made which is identical to the
original DNA
Replication of DNA
Recall Mitosis
Interphase
Mechanism of DNA replication
Interphase
Significance of DNA Replication
Significance of DNA Replication
• Allows DNA to make an
exact copy of itself
• Allows for Mitosis to
occur
• DNA can be passed
onto each new
generation of cells
Mechanism of DNA replication
1. Double Helix unwinds
2. An enzyme breaks the
bonds between the
base pairs
3. The two strands of the
original double helix
separate
Mechanism of DNA replication
4. DNA bases (in the
cytoplasm) enter the
nucleus
5. These bases attach to the
exposed complementary
base
6. Each side of the DNA acts
as a template for the new
DNA that forms
Mechanism of DNA replication
7. Each new double strand
rewinds to form a double
helix
8. Each new strand is
– Half new DNA
– Half original DNA
– Identical to the original
DNA double helix
DNA Profiling
Learning intentions:
● Describe the process of DNA profiling and
give two examples
● Describe genetic screening and give examples
● Compare DNA and RNA
DNA profiling
A method of making a unique pattern of
bands from the DNA of a person, which
can be used to compare with the DNA
profile of another person
Method of Preparing a DNA Profile
1. DNA is released from the cell
1. DNA is cut into fragments (using restriction
Enzymes) – cut at specific base sequences
1. DNA fragments are separated according to
their sizes (using gel electrophoresis) – small
fragments move through the gel faster than
larger ones
1. Patterns produced by the fragments are
compared/analysed
https://www.youtube.com/w
atch?v=MMG3ABcgmO0&ab_
channel=BiologyBugbears
Gel Electrophoresis
Gel
electrophoresis https://www.yo
utube.com/watc
h?v=vq759wKCC
UQ
Applications of DNA Profiling
1. Forensic Medicine
-Crime
2. Medical
Forensic Science
• DNA profiles can be
prepared from blood, hair,
saliva or semen let at a
crime scene
• DNA profile is compared
with victim and suspects 🡪
evidence
• Can also be used to
eliminate the suspect from
enquiry
DNA Profile Medical
• DNA profile can be used to determine if a person is the
parent of a child
• Blood samples are taken from child, mother and man
Genetic Screening
Testing DNA for the presence or
absence of a certain gene or an
altered gene
Genetic Screening
• If genes are altered in any way
will not code for correct protein Genetic Disorders caused
by defective Genes:
• Can have severe effects on
• Albinism
person who inherits such genes
• Two types of genetic screening:
1. Adult Screening
2. Foetal Screening
• Cystic-fibrosis
• Sickle cell anaemia
• Cancer
2007 Q10 b
RNA
Ribonucleic Acid
Very similar to DNA
• Both made up of a
sugar and bases
• Both contain 4 bases
• RNA contains:
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–
–
–
Adenine (A)
Uracil (U)
Guanine (G)
Cytosine
• RNA is a single strand
molecule
• RNA contains the sugar Ribose
• RNA bases are C, G, A and U
• RNA can move in and out of
the nucleus
• DNA is a double stranded
molecule – double helix
• DNA contains the sugar
Deoxyribose
• DNA bases are C, G, A and T
• DNA cannot move in and out of
nucleus – always in nucleus
Protein Synthesis
Learning intentions:
● Describe the process of protein synthesis
in 4 detailed steps
Protein Synthesis
Anabolic Process
Link….
What’s a gene?
Define Eukaryotic cell
Where is most DNA found?
Proteins
• Amino Acids join up to
make a protein
• Your DNA decides the
order that they join up in
(This is very important! )
• Do you remember the
organelle that makes
proteins?
BUT….how do we get the code out of
the DNA – trapped in the nucleus?
RNA!
tRNA
Nucleus
rRNA
mRNA
Protein synthesis
• mRNA
• tRNA
• rRNA
Messenger RNA
Transfer RNA
Ribosomal RNA
Learning intentions:
● Describe the process of protein synthesis in 4
detailed steps
Protein Synthesis
There are four stages:
1. Initiation
2. Transcription
3. Translation
4.
Protein Folding
Some Definitions:
Transcription:
Making messenger RNA (mRNA) using DNA as a
template
Translation:
The conversion of a sequence of genetic bases
on messenger RNA into a sequence of amino
acids
Initiation
Starting the Process
Initiation
1. Enzymes unwind the
DNA double helix
• It unwinds at the site of
the gene that is going to
produce the protein
2. Transcription
Making messenger RNA (mRNA) using DNA as a
template
Transcription (DNA RNA)
2. Complementary RNA
bases in the cytoplasm
move across the nuclear
membrane and match up
with exposed bases on the
DNA strand
3. RNA polymerase
(Enzyme) causes the RNA
bases to join together to
form mRNA
– Each mRNA has a
complementary base to
the DNA strand
– Every 3 bases of DNA or
RNA is called a
“triplet/codon”
Sidenote: Codons (or triplets)
There are three types of codons:
1. Start Codon:
Indicates the beginning of a gene (not involved in
protein production
2. Most codons:
The majority of codons in the gene specify particular
AA  produce protein
3. Stop Codon:
Indicates the end of a gene (not involved in Protein
production)
Transcription: DNA RNA
Every Gene has
(a) one start codon
(b) many codons
specifying amino acids
(c) one stop codon
Translation
Production of a protein using the
mRNA code
Translation
4. mRNA moves from the
nucleus to the cytoplasm
5. Ribosomes are made of
rRNA and protein
6. mRNA strand forms
weak bonds with the rRNA
in the ribosome.
Translation
• 7. tRNA molecules are
floating around in the
cytoplasm
Sidenote: What is tRNA
Each tRNA molecule carries
- A specific anticodon
- A particular amino acid which is specific to the
anticodon
Anticodon: a sequence of 3 bases on a tRNA,
that are complementary to a sequence of 3
bases on mRNA
In the cytoplasm of your cell….
Amino Acid
• Amino Acids are
floating around
AA
8
tRNA
Anti- Codon
G
Codon C
C
G
G
C
mRNA
• They are attached to
a “anti-codon”
• Codon: a sequence of
three bases in DNA
(or RNA) that codes
for a specific protein
Translation
• 8. tRNA molecules are
floating around in the
cytoplasm
9. tRNA molecules enter the
ribosome
10. The tRNA anticodons join
up with the complementary
mRNA codons – this brings AA
into ribosome
Translation
11. In the ribosomes the
AA are detached from the
tRNA molecules and are
bonded together to form
part of the new protein
12. tRNA leave the
ribosomes (no AA
attached) and pull the
mRNA strand with them
Translation
13. This process continues
until a stop codon is reached
• Once a stop codon is
reached
– mRNA code sequence is
complete
– New protein is produced
14. Once formed the protein
folds into the correct shape
Folding Protein
Three Types of RNA
Functions of the three types of RNA
Type or RNA
Function
mRNA (m=messenger)
• Complementary strand to DNA
• Carries the instruction for the production of a protein
from DNA to a ribosome
tRNA (t = transfer)
• Has complementary anticodon to mRNA codon
• Carries an amino acid to the ribosome
rRNA (r = ribosomal)
• Forms part of the structure of a ribosome
• Forms a weak bond with mRNA in the ribosome
Questions
2015 Q10 b
Write a note of each of the
following in relation t nucleic
acid - 3 points
i. Complementary base pairs
ii. Codon
iii. Transcription
Complementary base pairs
Codon
Transcription
DNA Profile
Protein Synthesis
Protein Synthesis