Starter
• Write three practical uses of PCR on a
show me board.
• Describe the purpose of PCR to your
partner.
Task
• Using your learning outcomes for key
areas 1.1 and 1.2, evaluate your
knowledge.
• You can use any method you like (ticks &
crosses, smiley and sad faces, colour
codes).
Key Area 1.3
Control of Gene Expression
Outcomes Covered
KA1.3
(a) Protein Synthesis
Learning Outcomes
1. Describe the basic structure of an RNA nucleotide
2. State the differences between DNA and RNA
3. Name the three types of RNA and state their
functions
4. Name each stage of protein synthesis and their
location
5. Describe stage one of protein synthesis
6. Identify complementary base pairs between DNA
and RNA
7. Name the enzyme used in stage one
RNA – Ribonucleic Acid
RNA is made up of a
single strand of
nucleotides.
phosphate
base
ribose sugar
Each nucleotide
consists of a
phosphate group, a
ribose sugar and a
base.
There are four bases:
1. Adenine
2. Uracil
3. Guanine
4. Cytosine
Comparison of DNA and RNA
DNA
RNA
Type of
sugar
deoxyribose
ribose
Bases
adenine, cytosine, guanine
and thymine
adenine, cytosine, guanine and
uracil
Number
strands
two
one
Location
only in nucleus
moves from nucleus to
cytoplasm
THINK PAIR SHARE
• What type of RNA do you already know
about and what’s its function?
Three Types of RNA
1. mRNA (messenger) – copies the code from
the DNA molecule and carries it to the
ribosomes.
2. tRNA (transfer) – found in the cytoplasm
where it binds to specific amino acids and
transports them to the ribosome.
3. rRNA (ribosomal) – forms a complex with
protein molecules to make the ribosome.
Show me board task
• On your board, write down as much as
you know about protein synthesis.
Protein Synthesis
• Protein synthesis has two stages:
1. Transcription
2. Translation
Transcription
transcribe – to make a copy
• The first stage of protein synthesis
takes place in the nucleus.
• RNA polymerase unwinds the DNA
strand.
• Hydrogen bonds are broken and the
bases are exposed.
RNA polymerase
Transcription
• Free mRNA nucleotides in the nucleus
form complementary base pairs with the
coding strand of the DNA.
Coding
strand
DNA base RNA base
Adenine
Uracil
Thymine
Adenine
Guanine
Cytosine
Cytosine
Guanine
RNA polymerase
Non - coding
strand
• Weak hydrogen bonds form between bases.
Transcription
• Strong chemical bonds form
between the phosphate of one
nucleotide and the ribose of the
next nucleotide, building the
mRNA strand.
• RNA polymerase can only add
nucleotides to the 3’ end of the
growing mRNA molecule.
• The weak hydrogen bonds that
were holding the DNA and
mRNA strands together break,
allowing the mRNA primary
transcript to leave the nucleus
and enter the cytoplasm.
A triplet of bases on mRNA is called a codon.
Transcription
• Hydrogen bonds reform between the
two DNA strands and the DNA molecule
rewinds to form a double helix.
transcription animation
You should now be able to . . .
1. Describe the basic structure of an RNA nucleotide
2. State the differences between DNA and RNA
3. Name the three types of RNA and state their
functions
4. Name each stage of protein synthesis and their
location
5. Describe stage one of protein synthesis
6. Identify complementary base pairs between DNA and
RNA
7. Name the enzyme used in stage one
Starter/Task
DNA and RNA molecules are found in the cells of both
eukaryotes and prokaryotes. DNA molecules are doublestranded whereas RNA molecules are single-stranded.
(i)Give two other structural differences between DNA
and RNA.
(ii) Describe the function of RNA polymerase in the
synthesis of a primary transcript.
Learning Outcomes
8. Describe the process of RNA splicing to
form a mature transcript
9. Describe stage two of protein synthesis
10. State the function of start and stop
codons
11. Identify complementary base pairs
between mRNA and tRNA
RNA Splicing
• There are long stretches of DNA that do not
play a part in the coding to make proteins.
• Non-coding regions are called introns.
• The introns are removed in a process called
RNA splicing.
• The exons are coding regions and are joined
(spliced) together to form mature transcript.
Task
• Collect two different coloured
highlighters or two different coloured
sheets of paper to help you form your
next note
RNA Splicing
5’
After the primary transcript has been
produced, the introns must be cut out.
3’
3’
5’
The exons join together to produce a
mature mRNA strand.
5’
3’
RNA Splicing
RNA splicing
Producing Different RNA
Transcripts
• Depending on which RNA segments are
treated as exons and introns different
segments can be spliced together to
produce different mRNA transcripts.
Translation
• The second stage of protein synthesis
takes place in the ribosome.
• Translation is the synthesis of protein
as a polypeptide chain under the
direction of mRNA.
• The process requires energy, in the
form of ATP.
transfer RNA (tRNA)
• Found in the cytoplasm.
• Composed of a single strand of
nucleotides.
• Hydrogen bonds between it’s
nucleotides cause the tRNA to fold back
on itself creating a 3D structure.
transfer RNA (tRNA)
• Each molecule of tRNA has only one
particular triplet of bases exposed.
• This triplet is called an anticodon.
• Each anticodon is complementary to an
mRNA codon.
• Each tRNA molecule carries a specific
amino acid at its attachment site.
tRNA
Translation
• There are many different types of
tRNA in one cell.
• Each tRNA picks up it’s specific amino
acid at it’s site of attachment and
carries it to the ribosome.
• The amino acid is added to the growing
end of the polypeptide chain.
Ribosome
• Ribosomes contain
ribosomal RNA (rRNA)
and enzymes essential
for protein synthesis.
• The function of a
ribosome is to bring
tRNA molecules in
contacts with mRNA.
• Ribosomes have one
binding site for mRNA
and three binding sites
for tRNA.
Ribosomes
• tRNA binding site P holds the
tRNA carrying the growing
polypeptide chain.
• Site A holds the tRNA carrying
the next amino acid to be joined
to the growing chain by a peptide
bond.
• Site E discharges a tRNA from
the ribosome once its amino acid
has becomes part of the
polypeptide chain.
Translation
translation animation
•
Translation
A molecule of tRNA carrying its specific
• amino
Beforeacid
translation
can begin,
a ribosome
(methionine)
becomes
attached
must
the 5’ end
of the mRNA
at
sitebind
P bytohydrogen
bonds.
template.
• The
mRNA codon at site A then forms
bonds
with its start
complementary
• hydrogen
This allows
the mRNA’s
codon
anticodon.
(AUG) to be in position at binding site P.
Translation
• When the first two amino acid
molecules are adjacent, they become
joined by a peptide bond to make a
polypeptide chain.
Translation
• As the ribosome moves along one codon, the
tRNA that was at site P moves to site E and is
discharged from the ribosome to be reused.
• The process continues to be repeated allowing
the mRNA to be translated into a complete
polypeptide chain.
Translation
• Eventually, a stop codon on the mRNA is
reached.
• Site A on the ribosome becomes occupied
by a release factor which frees the
polypeptide from the ribosome.
Polyribosome
• A single molecule of mRNA is used to
make many copies of the polypeptide.
• This multiple translation is achieved by
several ribosomes becoming attached at
the same time.
• This string of ribosomes on the same
mRNA molecule is called a
polyribosome.
You should now be able to. . .
• 8. Describe the process of RNA splicing
to form a mature transcript
• 9. Describe stage two of protein
synthesis
• 10. State the function of start and stop
codons
• 11. Identify complementary base pairs
between mRNA and tRNA
Starter/Task
Outcomes Covered
KA 1.3
(b) Expression of Proteins
Learning Outcomes
1. State at which two points the mechanism
of changing a protein can occur
2. Describe the process of alternative RNA
splicing
3. Name the two types of post-translational
modification
4. Name the component of a glycoprotein and
state its function
5. Name the components of a regulatory
protein and state how it is activated
One gene, many proteins...
• Until very recently, it was thought that
each gene could produce only one
protein
• The human genome contains between
20,000 and 25,000 genes
• However, there are in excess of 1
million proteins.
Altering proteins
• The mechanism to produce different
protein can occur at two points:
1. After transcription
2. After translation
After transcription
• Modification after transcription is
‘Alternative RNA splicing’.
• mRNA can be edited by assembling a
different sequence of introns and exons
for translation.
• Many mature transcripts of mRNA can
be derived from the same sequence of
DNA.
Alternative RNA splicing
Alternative RNA splicing
• Arranging exons in different patterns
enables cells to make different proteins
from a single gene.
After translation
• Modifications after translation are
‘Post- translational modifications’
• Two types of post-translational
modification that may be required for
protein function are
1. Cleavage
2. Molecular addition
1. Cleavage
• A single polypeptide chain may need to
be cleaved (cut) by enzymes to become
active.
Cleavage in insulin
• Insulin becomes active when a central
portion is cleaved.
• This leaves 2 chains joined by sulphur
bridges.
2. Molecular addition
• Protein structure can be changed by
adding carbohydrate or phosphate.
• Altering structure will change its
function, adding to the diversity of
proteins produced from a single gene.
Adding carbohydrate
• Adding carbohydrates to a protein
produces glycoprotein
• Glycoproteins normally function as
signalling, membrane and recognition
molecules
Adding phosphate
• Adding phosphate to a protein usually
forms a regulatory protein
• These will be inactive until
phosphorylated (phosphate added)
You should now be able to . . .
1. State at which two points the mechanism of
changing a protein can occur
2. Describe the process of alternative RNA
splicing
3. Name the two types of post-translational
modification
4. Name the component of a glycoprotein and
state its function
5. Name the components of a regulatory protein
and state how it is activated
Starter
From your knowledge of N5:
Describe simply how proteins are
produced.
Outcomes Covered
KA 1.3
(c) Gene Expression and Protein Structure
Learning Outcomes
1. Define the terms ‘genotype’ and ‘phenotype’
2. Describe how environmental factors can affect an organisms
phenotype
3. Define the term ‘gene expression’
4. Name the chemical elements found in proteins
5. Name the type of bond that links amino acids together
6. Name the chain formed when amino acids link together
7. State the consequences to the structure of this chain when
hydrogen bonds form between the amino acids
8. Describe the effect of further linkages (tertiary structure) on
the protein
9. Describe the quaternary structure of a protein
10.Names the four categories of proteins and describe their
function
Genotype
• The genotype of an organism is
determined by the sequence of DNA
bases in its genes
– The genetic code
• Some species have a genetic code that
is quite similar to another species
Phenotype
• The phenotype of an organism is its
physical and chemical appearance
• This depends on the proteins that are
synthesised in that cell
• Protein synthesis depends on gene
expression
Phenotype
• Production of phenotype/protein can be
affected by environmental factors
acting inside or outside of the cell.
Gene expression
• The nucleus of every cell in an organism
contains the same genetic information
• Genes are switched ‘on’ or ‘off’ in cells
to make a specific protein. This is
expression.
• No-one wants a hairy eyeball.....
Proteins
• Proteins are composed of carbon,
hydrogen, oxygen and nitrogen.
• Sometimes they contain sulphur
Proteins
• Proteins are made up of subunits
– Amino acids
• There are 20 different types of amino
acid
• Proteins vary in sequence of amino acids
and length
Polypeptides (primary structure)
• Amino acids in a specific order become
linked by peptide bonds
• They form polypeptide chains
Hydrogen bonding (secondary structure)
• Hydrogen bonds can form between the
amino acids on a polypeptide chain
• The chain becomes folded or coiled
Folded (β sheet)
Coiled (α helix)
Further Linkages (tertiary structure)
• Hydrogen bonding brings different
parts of the polypeptide chain into
contact
• Cross connections between amino acids
occur
– Bridges(bonds) between sulphur atoms
– Charged bonds (+/- interactions)
– More hydrogen bonding
Further Linkages (tertiary structure)
• These cause the specific 3-dimensional
shape that gives each protein its
function
Quaternary structure
• Non-protein elements are added
– E.g. Iron in haemoglobin protein
Classes of proteins
• Proteins can be categorised by their
function
– Enzymes
– Structural proteins
– Hormones
– Antibodies
• The function is dependent on the
structure
Enzymes
• Enzymes increase the
rate of chemical
reactions needed to
sustain life
• The folding of the
protein exposes an
active site. The active
site is complementary
to a specific substrate.
Structural protein
• Structural proteins play a vital role in
the structure of every cell
– E.g. Membrane protein
Hormones
• Hormones have a regulatory role in
growth and metabolism.
• They act as chemical messengers that
travel in the blood.
E.g. Insulin in regulation of blood glucose
Q. How would the action of insulin impact
the availability of ATP in the body?
Antibodies
• Antibodies are produced by white blood
cells to defend against foreign antigen