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Explain the Structure of DNA

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

'Explain the Structure of DNA' worksheet

Key stage:  KS 4

GCSE Subjects:   Biology: Single Subject

GCSE Boards:   OCR 21st Century

Curriculum topic:   You and Your Genes

Curriculum subtopic:   What is the Genome and What Does It Do?

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

We are our DNA! As this chemical is what all genetic information is made up of.

 

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.

 

[Reminder: A protein is a folded polymer with a specific sequence of amino acids.]

 

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, linking together to make the double helix.

 

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 sections are like on-off switches for coding DNA- they control gene expression by telling the cell to use or ignore certain genes, making sure we only get the proteins we need!

 

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. The double helix is unzipped and a complementary copy is made of the DNA on one side, with this new copy being called mRNA.

 

3. mRNA travels out into the cytoplasm.

 

Translation:

4. As the mRNA is read, 100s to 1000s of amino acids are brought in and joined in the sequence the genes state, making the initial protein chain.

 

After protein synthesis, the polypeptide then folds into a specific 3D structure that makes the protein suitable for its function, like an enzyme and its active site.

 

So clearly we’re super dependent on DNA, and any change to it can have huge consequences!

 

 

 

 

But change happens, and when our DNA changes, we call this a mutation.

 

Mutations can therefore change proteins by altering our coding and non-coding DNA, but usually, their function is preserved, and little difference is seen in our appearance (our unique 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, starting with the largest:

 

Column A

Column B

1. (Largest)
Double Helix
2.
Nucleotide
3.
Gene
4. (Smallest)
Nucleus

DNA is a polymer because it is made of many small units called?

Label the picture of the nucleotides below: 

 

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

What is the definition of a gene?

 

They're large sections of DNA that provide instructions on amino acid ordering

They're small sections of DNA that provide instructions on amino acid ordering

They're small sections of DNA that provide instructions on protein folding

They're large sections of DNA that provide instructions on protein folding

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 is the role of mRNA?

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

Decide whether these steps in protein synthesis are a part of translation or transcription.

 

[Note: The events are NOT in the correct order]

  • Question 1

Put these terms into size order, starting with the largest:

 

CORRECT ANSWER

Column A

Column B

1. (Largest)
Nucleus
2.
Double Helix
3.
Gene
4. (Smallest)
Nucleotide
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. When our DNA is unravelled, we see that it exists in as two linked strands in a swirl called the double helix. Number 4 is a gene and the smallest term is a nucleotide, but to learn more about these, press on with the next set of questions!
  • Question 2

DNA is a polymer because it is made of many small units called?

CORRECT ANSWER
NUCLEOTIDES
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 how it bonds gives DNA it's 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

What is the definition of a gene?

 

CORRECT ANSWER
They're small sections of DNA that provide instructions on amino acid ordering
EDDIE SAYS
Zooming in on the DNA more and more closely, a gene is a small piece of the double helix strands, 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 the cell reads and joins a certain set of amino acids from. But a lot of 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 reads and doesn't read, making it the controller of GENE EXPRESSION or gene visibility, as all cells have all the possible genes, but each cell uses different wants to only make the combinations of proteins they need for their function! If it wasn't for non-coding DNA, we may be a frog or have 2 hearts, all stopped because we have an on-off switch for parts of our DNA!
  • 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 is the role of mRNA?

CORRECT ANSWER
EDDIE SAYS
Here, we're tackling one molecule in the whole protein synthesis process. mRNA stands for messenger RNA as it carries a single-stranded DNA copy called RNA out of the nucleus and into the cytoplasm, where it's decoded and amino acids are joined to make proteins. This may be a completely different way of looking at both genetics and proteins, but don't worry if it's confusing at first, stick with and just practise practise practise! The best tip is to get lots of different diagrams and pictures from textbooks and Google to help you visualise all these new terms and processes, and I'm sure you'll get it in no time!
  • Question 9

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 10

Decide whether these steps in protein synthesis are a part of translation or transcription.

 

[Note: The events are NOT in the correct order]

CORRECT ANSWER
EDDIE SAYS
Firstly, it's important to know that transcription comes before translation, and transcription takes place in the nucleus while the second stage is in the cytoplasm. So the true order of events is: 1. The cell reads the gene but the DNA is too big to leave the nucleus so a messenger needs to be made. 2. The double helix unzips and a complementary copy strand is made from one of the double helix strands, and we call this mRNA. 3. This copy leaves the nucleus and goes to the cytoplasm. Now translation begins: 4. The mRNA is read and amino acids are selected in the same sequence as the genes have said (and the mRNA relays) 5. This specific sequence of amino acids is then linked together to make the unique protein intended by the cell. Note: To complete the whole process, protein folding takes place so it can have the shape needed for its job, but this happens AFTER protein synthesis, not during!
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