National 5 Biology
Unit 1: Cell Biology
Chapter 4: DNA and the Production of
Proteins
Part 1 - DNA
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National 5 Biology
Learning Intentions
By the end of today’s lesson you should aim to:
a.
Understand the structure of DNA:
• Specifically that the double-stranded helix held by complementary base
pairs, and that DNA carries the genetic information for making
proteins.
• You should be able to describe that the four bases Adenine, Cytosine,
Guanine and Thymine (A, C, G and T) make up the genetic code.
• And that A is always paired with T and C is always paired with G.
• The base sequence determines amino acid sequence in protein.
b) Know through research the relationship between chromosomes, genes,
DNA and protein to illustrate that genes are located on chromosomes.
c) Be able to demonstrate DNA structure by construction of 2D or 3D DNA
models (these must show base pairing!
d) Carry out numeracy activities to Carry out numeracy activities to determine
base pair numbers.
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Watson & Crick proposed the double helix or spiral
staircase structure of the DNA molecule in 1953.
In 1962 they were awarded the Nobel Prize for their work.
STARTER TASK: 10 minutes
What is DNA?
How are characteristics
passed on?
Passing on characteristics
In all living things,
characteristics are
passed on in the
chromosomes
__________ that
inherit
offspring ______
from their parents.
Chromosomes are
DNA
made of ____.
Where are chromosomes found?
Chromosomes are long strands of genetic information
nuclei
(DNA molecules) located in the _________
of cells.
one
chromosome
from mother
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Every individual has two genes for each
characteristic, one from mum and one from dad
• The chromosomes carry thousands of genes
along their length.
• Each gene codes for a different physical
characteristic.
• Different forms of genes are called alleles.
• These alleles are in competition with each
other.
• Some alleles are dominant and some are
recessive.
• When a dominant allele pairs up with a
recessive allele, the dominant allele ‘wins’ and
causes the final effect.
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Each gene codes for a
different physical
characteristic.
How is this achieved?
Each gene codes for
protein
one ________!
Slight differences in
alleles code
the genes (giving different ______)
for slightly different
proteins This causes the differences in
_______.
variations between
characteristics called _________
members
of the same species.
The Structure of DNA
DEOXYRIBONUCLEIC ACID
The double helix ‘ladder’ of a DNA molecule is held
together by ‘rungs’ made from pairs of chemicals called
______.
bases These strands are held together by weak bonds
between the bases
four types of
There are ____
A
bases, and they are
C
usually identified by their
initials.
How do you think the
four bases are paired?
adenine
cytosine
G
guanine
T
thymine
A molecule of DNA consists of two strands
twisted together into a double helix
http://news.bbc.co.uk/hi/english/static/in_dep
th/sci_tech/2000/human_genome/stage_3.st
m
Base pairs hold the 2 strands of the DNA helix together.
The rules for base pairing are…
‘A’ always pairs with ‘T’
A
Adenine
T
Thymine
‘C’ always pairs with ‘G’
C
Cytosine
G
Guanine
There are millions of base pairs in a DNA molecule, and
they always follow these rules.
It is the order of these bases along a DNA molecule that
genetic code
forms the ________
_____ – it’s that simple!
Sequence of DNA Bases
• The DNA of one member of a species differs
from that of another member by order in
which the bases order in their chromosomes.
• It is this sequence of bases along the DNA
strand that is unique to an organism.
• The sequence contains the genetic
instructions that control the organisms
inherited characteristics.
Genetic code
• All region of DNA on a chromosome is called a
gene and normally it is hundreds or even
thousands of bases long.
• The information present in the DNA takes the
form of a molecular language called the Genetic
Code.
• Amino acids are the building blocks of proteins.
• Each group of three bases along a DNA strand
represents a ‘Codeword’ for one of 20 types of
amino acids that make up protein.
Task: Organism to base pair worksheet
• Cut out the names
and definitions.
• Arrange the names i
order of size.
• The largest at the top
down to the smallest.
• Then match the
definitions to the
names.
DNA is composed of 4 nucleotide bases
A,T,C &,G arranged in pairs.
The backbone of DNA is based on a
repeated pattern of a sugar group and
a phosphate group. The full name of
DNA, deoxyribonucleic acid, gives you
the name of the sugar present deoxyribose.
phosphate
group
Higher/
Extension work!
A
Adenine
deoxyribose
sugar
nucleotide
base
C
Cytosine
T
Thymine
G
Guanine
Remember adenine always pairs with thymine and
vice versa. Guanine always pairs with cytosine and vice
versa.
There are weak hydrogen bonds between the base
pairs which hold the two strands together.
The two strands are twisted to form a “double helix”.
DNA molecules are composed of hundreds of
thousands of base pairs (A-T or G-C). The molecule is
double stranded and has a ladder like structure - the
base pairs forming the rungs and the strands the
uprights.
TASK : Model DNA – In Groups
20 minutes
Using the materials provided make a
model of part of a DNA molecule.
You will have to use it as an aid to
explain the structure of DNA.
http://www.wikihow.com/Make-a-Model-of-DNA-Using-CommonMaterials
http://www.youtube.com/watch?v=iNztJjHKw98
TASK: DNA ORAGAMI –
with template and You tube
http://www.youtube.com/watch?v=0jOapfqVZlo
TASK -Edible: Model DNA
YOU NEED...
• Sweets .e.g, cocktail sticks
• Patience and Expertise
http://www.youtube.com/watch?v=QnpLMaWjhhc
Virtual build a DNA molecule
http://learn.genetics.utah.edu/content/molecules/builddna/
Mr W’s DNA RAP
http://www.youtube.com/watch?v=wdhL-T6tQco
Cartoon
Numeracy activity (ps): Question1
• If there a section of DNA contains 24,000
bases and 20% are cytosine, how many
adenine bases should there be?
A. 2400
B. 4800
C. 7200
D. 14400
Numeracy activity (ps): Question2
• If a DNA double helix contained 100 base pairs
and there were 40 cytosines, how many
adenines would there be?
Numeracy activity (ps): Question3
• 20% of the bases in a DNA molecule are G.
What % of the bases are A?
A. 20%
B. 30%
C. 40%
Numeracy activity (ps): Question 4
• A piece of DNA contains 500 bases in total,
150 of these are adenine. What percentage of
the DNA is adenine?
Numeracy activity (ps): Question 5
A fragment of DNA was found to have 120
guanine bases and 60 adenine bases. What is
the total number of sugar molecules in this
fragment?
A. 60
B. 90
C. 180
D. 360
Numeracy activity (ps): Question 6
A DNA molecule consists of 4000 nucleotides of
which 20% contain the base adenine.
How many of the nucleotides in this DNA
molecule will contain guanine?
A.800
B.1000
C.1200
D.1600
Numeracy activity (ps): Question 7
How many adenine molecules are present
in a DNA molecule of 4000 bases, if 20% of
the base molecules are cytosine?
A. 400
B. 600
C. 800
D. 1200
National 5 Biology
Unit 1: Cell Biology
Chapter 4: DNA
and the Production
of Proteins
Part 2 – Protein
Synthesis
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National 5 Biology
Learning Intentions
By the end of today’s lesson you should be able to:
1. Describe that Messenger RNA (mRNA) is a molecule which
carries a complementary copy of the code from the DNA, in
the nucleus, to a ribosome, where the protein is assembled
from amino acids.
2. Have performed research on leading biologists of this area,
e.g. Watson and Crick, Rosalind Franklin, Maurice Wilkins,
Chargaff.
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Homework: Research task
History of DNA Discovery
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Watch this for homework:
You can also look at pg 31 Torrance
http://www.youtube.com/watch?v=j3jRH2fXieY
What is it?
Proteins are needed for:
•
Growth (including making new cells)
• Repair of damaged tissue
• Building structures
–Muscle
–Bone
–Skin
–Hair
–Enzymes
–Antibodies
–Hormones
How the Genetic Code Works
Our bodies are made from
hundreds of thousands of
different kinds of
protein
_______.
Small differences in the
proteins that our bodies
are made of account for
physical ___________
differences
_______
between us.
Each gene codes
for one protein.
______
Genes code for the
proteins, so small
differences in our
genes cause the
differences between
our proteins, and so
the differences
between us.
Making proteins
• Proteins are long molecules made up of
amino acids.
protein
molecule
amino acid
• There are 20 different types of amino acid
from which to make proteins.
• Different combinations of amino acids make
different proteins.
For Example
protein
molecule 1
amino acids
What happens if the amino acids are in a different order?
protein
molecule 2
How does the
cell know what
order the
amino acids
should be in?
Genes, we can investigate this in organisms by
locating genes on the chromosome.
By comparing 2
organisms with different
traits for the same
characteristic (e.g. eye
colour) we can learn
about the positioning and
importance of genes on a
chromosome.
The diagram shows two
identical flies with the
exception of eye colour.
When chromosomes are
compared their genes
are identical. EXCEPT for
one band present in red
eyed fly but absent in
white eyed fly.
How do Genes make proteins?
• Each amino acid is coded for by its own special
sequence of three bases called a triplet.
triplet
amino acid
How do genes make proteins?
• The order of triplets in a gene determines the
sequence of amino acids.
• The amino acids join together to form a protein
molecule.
Once we have a chain of amino acids…
• … then the protein is folded to take on its final shape (the
amino acid sequence has determined this shape).
• And it is this shape that allows each protein to perform
its particular function.
Is that all there is to it?
NO!
It’s actually more complicated than that.
THINK!
Where is DNA found?
What structures make proteins?
Where are they found?
Watch the video on making proteins and see if
you can find the solution…
The genetic code for proteins
The story of protein synthesis
So how does the coded information on the
DNA get out into the cytoplasm?
instructions
Genes don’t make proteins – they just contain the _____________
on how to make them.
BUT… DNA stays in the nucleus and proteins are built in the cell’s
cytoplasm
___________.
DNA
mRNA
Protein
• DNA is kept in the nucleus to keep it safe.
• A specific sequence of this DNA is a gene to make a
protein.
• This sequence is copied, so it can be taken out of the
nucleus.
• This copy is called messenger RNA (mRNA).
• The mRNA takes the copied instructions out of the
nucleus and into the cytoplasm.
• In the cytoplasm, the mRNA is ‘read’ by a ribosome
which uses the code to make the protein from amino
acids.
DNA
mRNA
Protein
Complete the diagram using the following words:
Gene
mRNA
Chain of
amino acids
DNA
Ribosome
Cell
Membrane
Nucleus
DNA
mRNA
Protein
Not really
National
5 work
order
mRNA is a molecule
different
from
DNA -but
canin
you
suggest how?
to play genetic code games you
need to know this.
A short section of mRNA
• mRNA has only one strand not two like DNA
• In mRNA thymine is replaced by U (uracil)
U
DNA inside the
nucleus coding for a
protein.
DNA opens so that
mRNA may be
copied from it .
mRNA is made using
DNA template. This
is called
transcription.
mRNA peels off the
DNA template.
mRNA goes out into the
cytoplasm through a
nuclear pore.
A real mRNA molecule
would be much longer
than this - the length of
a whole gene.
mRNA travels to a
ribosome.
Out in the cytoplasm
special carrier molecules
pick up amino acids.
mRNA moves into the
ribosome so that the code
it carries may be “read”.
Bases on the carrier
molecules lock on to
corresponding bases on
mRNA.
This brings the amino
acids into line with each
other and they bond
together.
The carrier molecules go
off into the cytoplasm to
collect more amino acids.
More carrier molecules continue to “read” the mRNA
code adding amino acids and building the chain that
will eventually become a protein.
TASK:To recreate the process by
which a cell produces a protein.
• Each group of desks represents
a ribosome.
• The teacher’s desk is the
nucleus. It contains the DNA
sequence from which you are
going to make your protein.
DNA:
ATCGGCATTCGCACGATCCGCAGCATT
INSTRUCTIONS
• One member of the
group collect:
Amino acids
Sellotape
White board
• One member of the
group should nominate
themselves to be
mRNA. You should come
to the nucleus, “unzip”
the DNA and transcribe
the sequence.
• Sort the bases on the
mRNA molecule into
codons.
• Use the protein
decoder to work out
which codon makes
which amino acid.
• Put your amino acids
together in the correct
sequence.
• Have your protein
checked by the teacher.
When the mRNA strand reaches the
ribosome the amino acids must be joined in
the order coded for by the mRNA strand.
Codon on mRNA
Amino acid
GCG
Pink
UAA
White
UAG
Blue
UCG
Red
CCG
Green
UGC
Yellow
Did you manage? - The Answers
DNA:
ATCGGCATTCGCACGATCCGCAGCATT
mRNA:
UAG CCG UAA GCG UGC UAG GCG UCG UAA
Amino acids:
blue-green-white-pink-yellow-blue-pink-red-white
Activity: Codon Bingo
Activity: DNA and Proteins Bingo
ribosome
cytosine
chromosome
double helix
messenger RNA
guanine
twenty
gene
sequence
shape
adenine
three
protein
base
thymine
amino acid
DNA
Question time
• How many DNA bases code for each amino acid?
• Explain how different genes code for specific
proteins.
• Humans have about 20,000 genes. The two members
of each pair of chromosomes have the same genes on
them. So, on average, about how many genes do you
think there are on each of your chromosomes?
• When you eat proteins from meat, eggs or soya beans
your body uses them to make the proteins in your
cells and tissues. How do you think this happens?
What happens if…
Sometimes there are errors in the
genetic code called mutations.
What do you think would happen if there was
an error in the genetic code for the enzyme
PAH, which breaks down phenylalanine from
food into useful products for the body?
Phenylketonuria
• If the code is wrong, the
protein is either not made or is
faulty.
• In this case, the protein made
has the wrong shape so can’t
carry out its job to break down
phenylalanine.
• Instead the concentration of
phenylalanine builds up in the
body to toxic levels.
A DNA Story
Your Instructions:
Your cast:
• Write a story, or
draw a comic about
how DNA is copied
and turned into
protein.
• It will feature a
specific cast of
characters and
explain how all of
the parts work
together.
The nucleus is
a library
The gene is a
DNA is a recipe
recipe for apple pie
book
mRNA = copy
of the recipe
The ribosome
is a kitchen
The protein made
is an apple pie
Now collect the cut and use it to tell your
neighbour the story of protein synthesis.
Do not cut around every
base as this will be too
fiddly and takes ages. Just
cut up to very near the
bases as shown so that you
can match them up with
corresponding bases.
ALTERNATIVE
STORY
ACTIVITY
Articulate!
Ribosome
Cytosine
Messenger
RNA
Gene
Chromosome
Adenine
Base
Amino Acid
Double helix
DNA
Thymine
Protein
Guanine
Task TYK
• Complete questions 1 – 3. Torrance p33
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Task TYK – How did you do??
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Homework:
DNA and protein production
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