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Analyse the Structure of DNA

In this worksheet, students will learn the terminology used to analyse DNA's many different formats, explain the process of protein synthesis using DNA, and how genetic mutations can impact our bodies.

'Analyse the Structure of DNA' worksheet

Key stage:  KS 4

GCSE Subjects:   Biology: Single Subject

GCSE Boards:   Pearson Edexcel

Curriculum topic:   Natural Selection and Genetic Modification

Curriculum subtopic:   Natural Selection and Genetic Modification

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

We are our DNA!

 

Held in our cell nuclei, it’s a long chain of tightly wound-up coded instructions which cells unravel, read and use to make proteins or polypeptides.

 

When cells want to make a certain protein, they read DNA in chunks called genes that code for a specific sequence of amino acids.

 

Like proteins, DNA is also a polymer but of repeating nucleotides- a group made of a phosphate group on a sugar attached to a nitrogenous base.

 

Nucleotides link together to make the double helix structure of DNA.

 

There are 4 different bases, A, T, C, G, and they’re very specific about who they pair with:

Adenine with Thymine and Cytosine with Guanine

 

These groups are complementary base pairs, and they are joined by weak hydrogen bonds, linking the 2 double helix strands in the middle!

 

 

So far, we have only said that DNA codes for proteins. This is not entirely true, because there are two types!

 

CODING DNA are the genes the cells read and make proteins from

 

-NON-CODING DNA are like on-off switches for coding DNA- they control gene expression by telling the cell to use or ignore certain genes.

 

 

So to make a protein, there are two stages: TRANSCRIPTION of DNA (in the nucleus) and TRANSLATION (in the cytoplasm):

 

Transcription:

1. The cell reads the genes to get the amino acid order. But DNA is too big to get out of the nucleus to build the protein so it uses a messenger instead!

 

2. An enzyme temporarily breaks the weak hydrogen bonds and unzips the double helix 

 

3. Another enzyme called RNA polymerase binds to a non-coding gene in front of the gene it wants. Once here, it uses one side of the double helix as a template to make a copy of the gene, with this new complimentary copy being called mRNA.

 

4. The mRNA travels out into the cytoplasm and attaches to the site of protein synthesis- an organelle called a ribosome

 

Translation:

5.As the ribosome inspects the mRNA, it reads the nucleotide bases in groups of 3 called codons, with one codon coding for one specific amino acid.

 

6. Then another helper called transfer or tRNA brings 100s to1000s of specific amino acids to the ribosome in the sequence the genes state, which are then linked to make the initial polypeptide.

 

After protein synthesis, the polypeptide then folds into a specific 3D structure.

 

 

But change happens, and when the order of bases changes in our genes, we call this a mutation.

 

Mutations can, therefore, change proteins through our DNA, but usually, their function is preserved and little difference is seen in our phenotypes.

 

But rarely if enough of the DNA is changed, the protein’s shape can be altered so much that it can’t do its job, like an enzyme without a working active site!

Put these terms into size order by numbering them from 1 to 6, 1 being the largest:

 

Being made of many subunits called nucleotides, DNA is considered a what?

Label the picture of the nucleotides below: 

 

Which of these possible combinations of DNA bases (Adenine, Guanine, Cytosine and Thymine) are correct?

How many of these statements are true about genes?

 

They give instructions to cells about amino acid sequences

They're small sections of the double helix

They control what proteins are made by a cell

What is the purpose of DNA?

Column A

Column B

Coding DNA
Controls gene expression
Non-coding DNA
a gene that gives instructions about a specific se...

True or False:

 

'A mutation is a change to DNA that alters how we look'

TRUE or FALSE

What are the two stages of protein synthesis?

Transcription THEN Translation

Translation THEN Protein Folding

Translation THEN Transcription

Protein Folding THEN Transcription

Describe the process of transcription in protein synthesis, including the site of action in the cell, the enzyme involved and it's role and product, and where the stage ends. [8 marks]

Protein synthesis contains many specialised tools that assist the process.

Column A

Column B

mRNA
A triplet code of bases in a gene that are specifi...
tRNA
An enzyme that makes a COMPLEMENTARY copy of one s...
RNA Polymerase
a molecule responsible for the transfer of amino a...
A Codon
a messenger transporting a COMPLEMENTARY copy of o...
  • Question 1

Put these terms into size order by numbering them from 1 to 6, 1 being the largest:

 

CORRECT ANSWER
EDDIE SAYS
This is an important concept to appreciate, as if you understand this question, you have a good grip on how DNA is structured. The largest term here is the nucleus, which acts as the cell's storage house of DNA. All these other terms refer to zooming in on the DNA in the nucleus more and more closely, the entire bunch of genetic information being our genome. When the genome is unravelled, we see its DNA exists in as two linked strands in a swirl called the double helix. Number 4 is a gene, number 5 is a nucleotide and the smallest term is a base, but to learn more about these, press on with the next set of questions!
  • Question 2

Being made of many subunits called nucleotides, DNA is considered a what?

CORRECT ANSWER
POLYMER
EDDIE SAYS
How did you find this question? The smallest form of DNA if its nucleotides- little building blocks that bond together to form the iconic DNA spiral shape.
  • Question 3

Label the picture of the nucleotides below: 

 

CORRECT ANSWER
EDDIE SAYS
The arrangement of a nucleotide is important because these make the double helix shape. On the outside is a phosphate group, which is linked to a corner of a 5 sided sugar called a pentose sugar. The sugar then bonds to a base- depending on the nucleotide, this could be A, T, C or G, which then sticks out into the middle of the double helix, waiting to hydrogen bond to a base from a nucleotide from the opposite strand!
  • Question 4

Which of these possible combinations of DNA bases (Adenine, Guanine, Cytosine and Thymine) are correct?

CORRECT ANSWER
EDDIE SAYS
When the bases hydrogen bond in the center of the double helix, Adenine can only join to Thymine, and Cytosine can only join to Guanine. However, the initials can be switched around, for example both CG and GC are acceptable, as are TA and AT.
  • Question 5

How many of these statements are true about genes?

 

CORRECT ANSWER
They give instructions to cells about amino acid sequences
They're small sections of the double helix
They control what proteins are made by a cell
EDDIE SAYS
ALL TRUE! So, do you think you have a good grasp of all the definitions in this topic? Zooming in on the DNA more and more closely, a piece of its double helix is a gene, which acts as coded instructions to cells in how to make a specific protein. They do this by relaying a certain sequence of amino acids, making sure the correct combination is put together so the right protein is made for that cell by that cell.
  • Question 6

What is the purpose of DNA?

CORRECT ANSWER

Column A

Column B

Coding DNA
a gene that gives instructions ab...
Non-coding DNA
Controls gene expression
EDDIE SAYS
So it's important that we know that DNA does not always = proteins! Coding genes do what we know already and have a specific sequence of nucleotide bases that cells use to make certain proteins. But many genes are actually instructions for other genes and aren't connected to amino acids at all! Non-coding DNA control which coding genes the cells read and don't read, making it the controller of GENE EXPRESSION. All cells have the DNA to make every human protein, but each cell only makes the proteins that their function requires!
  • Question 7

True or False:

 

'A mutation is a change to DNA that alters how we look'

CORRECT ANSWER
TRUE or FALSE
EDDIE SAYS
This one was tricky but remember the intro! It\'s true that a mutation is when a gene changes- this can be natural but can also be caused by exposure to chemicals like radioactive toxins or cigarettes! They can sometimes be beneficial, sometimes dangerous, BUT often have no impact. So it is very RARE that a mutation has an obvious effect on our appearance or our PHENOTYPE.
  • Question 8

What are the two stages of protein synthesis?

CORRECT ANSWER
Transcription THEN Translation
EDDIE SAYS
Protein synthesis is transcription, THEN translation THEN protein folding as a part of translation!!! Think about it this way, transcribing is like when a secretary used to type while her boss was speaking so she could collect his instructions in a universally readable way- she was a transcriber! So we first have to write up DNA into a format that both the cell and the ribosome can read clearly, making mRNA, so transcription comes first. Then it\'s clearer that translation is second as we\'re taking this DNA copy and the ribosome is trying to translate all the instructions into an actual amino acid chain!
  • Question 9

Describe the process of transcription in protein synthesis, including the site of action in the cell, the enzyme involved and it's role and product, and where the stage ends. [8 marks]

CORRECT ANSWER
EDDIE SAYS
Many people find protein synthesis very confusing and a lot to remember, but as long as the student keeps breaking it all down into key steps, they'll find it a lot simpler. This question is an example of when a student might get a 6-8 marker asking them to describe a specific process, and here we've chosen to talk about transcription. Here's how to approach giving marks in this question: So, a small summary is that transcription is the first of two steps in making proteins- here, the cell reads DNA in its nucleus, makes a copy and sends it into its cytoplasm (main area). The easiest marks come from ANSWERING THE QUESTION which is where many students stumble when they're panicked and nervous. The question asks for you to state where the process is taking place and where it ends before stage 2 happens. So the first mark comes from mentioning that transcription happens in the nucleus. Next, the student needs to define or explain transcription, and say what role DNA or the sections of DNA called genes do in this process, giving the student up to 2 marks. Then for 3 marks, the student has to say something to the effect of the double helix is broken, i.e. the DNA structure is broken, and a copy of the DNA is made called mRNA. To fully answer the question which references an enzyme and its product, they have to define why we need mRNA or what it does, include that the enzyme RNA POLYMERASE makes mRNA (with additional information about binding to non-coding DNA showing the top level of students), so these four marks and the detail here are really what separate the good and great pupils in terms of understanding and revision. Finally, we need to answer the question again and say that the DNA copy called mRNA leaves the nucleus and goes to the cytoplasm where a structure called a ribosome is waiting for them. If the student puts that the mRNA travels into the cytoplasm implying it has left the nucleus, that's fine. Also, if they have not mentioned a ribosome, they can still have the mark as that's more relevant to the next stage rather than transcription, but the cytoplasm must be mentioned for the final mark. For the pupil, here are some tips about answering these types of long questions and how to think about them: - Remember that the examiner has a mark scheme with bullet points telling them to look out for keywords, so always mention key definitions or terms that you know your teacher has used non-stop in this topic because that'll get you very far on its own. - Then understand that any long processes can always be broken down into simple steps to remember, don't be intimidated by what the examiner or the teacher might expect, and remember that it's all doable as long as you have worked hard beforehand.
  • Question 10

Protein synthesis contains many specialised tools that assist the process.

CORRECT ANSWER

Column A

Column B

mRNA
a messenger transporting a COMPLE...
tRNA
a molecule responsible for the tr...
RNA Polymerase
An enzyme that makes a COMPLEMENT...
A Codon
A triplet code of bases in a gene...
EDDIE SAYS
Both transcription and translation have substances that assist them in protein production: mRNA is a messenger DNA code which is a copy of one stand of the unravelled double helix. It has to be made because DNA is too big to leave the nucelus and give instructions to the ribosome. In transcription, mRNA couldn't be made without the enzyme RNA polymerase, which latches onto a non-coding gene at the start of the desired section and then proceeds bringing in free nucleotides and piecing them together as it copies the strand, making mRNA. tRNA is used in translation and brings amino acids in the instructed sequence to the ribosome to be pieced together to make the protein. Finally, a codon is a 3 base section of a gene, with one codon (3 bases) coding for one specific amino acids, which is how DNA is read.
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