Download B2.10a - Science @ St John`s

B2.10a Modelling protein formation
Using models can help us understand more about some processes. The assembly line in a car factory
can be used as a model to describe how proteins are put together.
When making a car, you start with a design of a complete car that is then broken down into its component
parts. A plan is made of the order in which the parts must be put together to create a whole car. The plan
is used to construct the assembly line, where the component parts are added one at a time until each car
is complete.
To make the whole process simpler and faster, the cars move along the assembly line as they are being
built and the component parts are fitted at the same point on the line each time. This means that robots
specially designed to handle particular components don't have to move.
1
Draw a flowchart to explain how a car is put together on an assembly line.
2
Draw a flowchart to explain how a protein is put together in a cell.
3
Match the main stages of building a car to the main stages in building a protein and explain your
choices:
e.g. the DNA in building a protein is like the … in building a car because …
4
Explain the advantages of using a model to explain a complex process such as protein manufacture.
5
a
Describe any parts of the car assembly model that don't match protein manufacture well.
b
Is this a problem for understanding protein manufacture? Explain your answer.
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.
B2.10b Building proteins
Higher
You are going to build an amino acid chain starting from the DNA code. Remember that in complementary
base pairing, A (adenine) pairs with T (thymine), and C (cytosine) pairs with G (guanine). Also remember
that in RNA the base T is replaced by U (uracil).
Here is a sequence of bases from the coding strand of some DNA. This sequence codes for a sequence
of amino acids that begins with the amino acid Met (short for methionine).
TACCTGCGCCTTCATAGC
1
Copy the sequence. Then write down the sequence of bases in the mRNA strand that will form during
transcription.
The mRNA strand moves out of the nucleus into the cytoplasm and joins to a ribosome. The ribosome
reads the base sequence in triplets (codons).
2
Use brackets to mark the triplets on your mRNA strand.
In the cytoplasm there are many different kinds of tRNA. Each kind of tRNA has a different triplet of bases
and the triplet controls which amino acid is attached to the tRNA, as shown in the diagram.
Some of the different tRNAs found in cytoplasm attached to their amino acids.
Only the tRNA with the complementary triplet of bases will attach to a triplet on the mRNA strand on the
ribosome. Enzymes separate the amino acid from the tRNA and attach it to the growing amino acid chain.
3
Match the correct tRNAs from the diagram to the triplets on your mRNA strand. Write down the
sequence of amino acids in the chain that is formed.
4
Check your amino acid sequence with another student. If the sequences aren't the same, compare
each of your answers to find where the error occurred.
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.
B2.10c Making a protein
Jon and Felice were trying to make a model to explain how DNA controls the sequence of amino acids in
which proteins are made. They had some coloured popper beads in red, green, white, yellow, blue and
orange. They decided to use the first letter of each colour as the code for that colour of bead.
Jon wrote a code for a protein using these letters: G R R B W G Y B R W O Y.
1
In this model of how proteins are made:
a
what do the coloured popper beads represent
b what do the letters represent
c
what does the code that Jon wrote represent?
Jon gave Felice his letter code. Felice used the code to make a string of popper beads that matched the
order of the code.
2
Which colour was used most often in the string?
3
What does the string of popper beads represent?
4
What in DNA controls the order of amino acids when a protein is made?
When Jon and Felice wrote up their investigation they wrote:
Each of our letters is like the small groups of bases in DNA that code for different amino acids.
5
Complete their write-up to explain how this model helps to show how DNA controls which proteins are
made.
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.
B2.10d Codes for proteins
Higher
Name
Class
Date
You do not need to remember the details on this sheet for your exam but you could be asked to apply
your knowledge to unfamiliar situations.
The table shows how ribosomes decode the triplets of bases (codons) on an mRNA strand to make
proteins. Each triplet is the code for one particular amino acid. The shortened names of the amino acids
are shown in italics next to the triplet code.
Second position
U
U
First position
CUG
A
G
1
AUC
AUA
AUG
GUU
GUC
GUA
GUG
Phe
Phe
Leu
Leu
Leu
Leu
Leu
Leu
Ile
Ile
Ile
Met
Val
Val
Val
Val
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG
A
Ser
Ser
Ser
Ser
Pro
Pro
Pro
Pro
Thr
Thr
Thr
Thr
Ala
Ala
Ala
Ala
UAU
UAC
UAA
UAG
CAU
CAA
CAG
AAC
AAA
AAG
GAU
GAC
GAA
GAG
G
Tyr
Tyr
STOP
STOP
His
His
Gln
Gln
Asn
Asn
Lys
Lys
Asp
Asp
Glu
Glu
UGU
UGC
UGA
UGG
CGU
CGA
CGG
Cys
Cys
STOP
Trp
Arg
Arg
Arg
Arg
Ser
Ser
Arg
Arg
Gly
Gly
Gly
Gly
The table is not complete. Use the rules shown in the table to fill in the missing letters.
2
Use the table to find:
a how many different codons code for the amino acid serine (Ser)
b how many different codons there are in total, which code for an amino acid
c how many different amino acids there are.
3
The start of a DNA template strand of a gene looks like this:
TAC CGG TCG TGT AGG TGG TGG TAG
4
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
Third position
C
UUU
UUC
UUA
UUG
CUU
CUC
C
a
The complementary DNA strand to the template strand is called the coding strand. Write out the
first 24 bases of the coding strand for this gene.
b
Write out the first 24 bases of the mRNA strand for this gene. (Remember that, instead of T in
DNA, the base is U in RNA.)
c
Use the table to write out the first eight amino acids that this gene codes for.
What would be the coding strand of the gene that codes for the protein below? There is more than one
answer. Give just one solution.
Met-Phe-Lys-Trp-Asp.
Extra challenge
5
When scientists were trying to work out how many bases coded for one amino acid, they considered
codes that used one base per amino acid and then two bases per amino acid. Explain why three
bases was the smallest number that could possibly code for one amino acid.
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.