Gene Mutation

• Science
• Secondary Education

Teacher: Central dogma has been our key central focus in the last few lessons, can anyone explain to us what it is? 

Answer: the central dogma is a theory that explains how genetic information (DNA) can be used to make RNA (through transcription) that then can be transcribed to make new proteins. 

(Continue to slide 3) 

 Mutations 

Biology 30 

Molecular Genetics

Teacher: Hi all, welcome to biology 30. Today we will be learning about genetic mutations but before we do that let's review the concept of central dogma (go to slide 1). 

What do all of these have in common? 

Teacher: before we get started into our lesson, can anyone tell me what Spiderman(left) and teenage mutant ninja turtles have in common? (right) 

Answer: they are all mutants, just like us! 

What is a Mutation?

• Mutations are permanent changes in the sequence of the DNA molecule. 
• Individuals showing these changes are known as mutants 
• Mutations are the source of new genetic variation that may be acted on by natural selection. 

• Point three 
  

Teacher: 

We haven't talked about natural selection yet, that's our next unit! But just recognize mutations play an important role in creating genetic variation!

What Causes Mutations? 

Spontaneous mutations: mutations that occur as a result of errors made during DNA replication. 

•  DNA polymerase occasionally misses or misplaces a base during replication. 
  

Induced mutations: arise from exposure to mutagenic agents

•  UV radiation, X-Rays and certain chemicals 
  

Point 1

Teacher: DNA polymerase have the ability to proofread and fix the errors but sometimes errors are not caught, resulting in mutations to occur. 

Induced mutations: environmental factors also play a role in inducing  mutations (more on this later). 

Are mutations harmful?

Yes

No

Both

Teacher: perhaps there is a negative connotation associated with "mutation" because there is a common misconception where students believe all mutations are harmful. 

18:10 - 20:42

Before playing the video, ask students: is anyone lactose intolerant?  

• This is an example of how mutations can be beneficial to humans. 

Mutations can be harmful

•  Harmful mutations occur at low rates in a species.

Mutations can be beneficial 

•  Tends to become more common over time, leading to new evolutionary changes. 
  

Mutations may have no effect on the organism 

• having neither a benefit nor a cost

Types of Mutations 

Point Mutation 

Point Mutations: changes in a single or few base pair of a DNA sequence 

1.  Involves the substitution of one nucleotide for another 

Silent Mutation: amino acid is NOT changed 

Missense mutation: amino acid is changed 

Nonsense Mutation: amino acid is changed to a STOP codon 

Silent mutations occurs when a base is subsisted does not cause a new amino acid to be coded for. 

This outcome is more likely to happen. 

Silent Mutation: a mutation that does not result in a change in the amino acid coded for. 

• Occurs when a base is substituted for another base 
• Has no effect on the operation of the cell and do not affect protein structure 

Most mutations are silent. 

Repeat this visualization/drawing of how mutations changes protein synthesis for each of the following. 

Teacher: walk through this example with students. Draw this example on the whiteboard and mutate the top strand (G substituted to an A)

Ask the student, when G is substituted to an A, what happens to the complementary strand? 

ANS: because the strands are complementary, the base will also change. 

Ask the student: What is going to happen when the DNA is transcripts into mRNA? ANS: Base C change to U because mRNA must be complementary to the DNA template strand. 

Ask the student: what do you notice about the amino acid coded for?

  ANS: the amino acid coded for did not change even though a mutation occurred in this DNA bases. 

*Show students this slide after they have completed the activity above

Mis-sense Mutation: arises when a change in a base sequence of DNA alters a codon

• leading to a different amino acid being placed in the polypeptide 

Mis-sense mutation arises when a substitution in the base sequence of DNA causes a change in the amino acid coded for. 

• may affect the protein function and structure

Repeat the activity from previous, but this time, have students come to the white board and draw the effects of this mutation on the DNA, RNA + amino acid. 

While the student is in front, ask: 

1. A mutation happens in the original strand non-mutated strand, what happens when it goes through DNA replication? 

2. When the DNA goes through transcription, what happens to the mRNA?  is there a change? 

How does this affect the protein coded for? ANSWER: Gly changed to Ser

- these are guiding questions that should help the student walk through the example. 

Sickle cell anemia 

caused by a single base pair substitution in the gene that codes the B hemoglobin polypeptide 

affects the 7th codon, Glu changed to Val 

the hemoglobin still functions but it folds differently, changing the shape of the rbc 

example of missense mutation 

Interesting fact: 

individuals that are heterozygote for sickle cell anemia have a survival advantage against malaria over people who are homozygote (two copies of the mutation) in regions where malaria is endemic or severe. 

Nonsense mutation: occurs when a change in the DNA sequences causes a stop codon to replace a codon specifying an amino acid. 

1. Results in premature stop signal where a large protein could be lost if the nonsense mutation occurs early in the mRNA
   

Nonsense mutation occurs when the base substitution codes for a new amino acid that causes  introduces a premature stop during translation. 

Repeat the activity from before, ask students to note the location of stop codon. 

What is the effect on the protein? 

ANS: in this situation, the mutation introduces a premature stop in the second stop, a large amount of protein is lost as a result. 

Frameshift Mutations 

causes a change in the reading frame 

Deletion: occurs when one or more nucleotides are removed from the DNA sequence 

Insertion: the placement of an extra nucleotide in the DNA sequence 

Base substitutions can result in silent, nonsense or missense mutations. 

On the other hand, deletion and insertions causes frameshift mutation. 

• remember that the nucleotides are read in triplets 

Insertion

Have another student volunteer again to visualize/draw out what is happening during protein synthesis when there is an insertion mutation. 

• In this particular example, the insertion of an extra nucleotide introduces a pre-mature stop. Is this also a nonsense mutation?

ANSWER: nonsense mutation happens due to base substitution. In this example, it just so happens that the base inserted caused a premature stop. 

no longer read in multiples of three. 

Is This a Nonsense Mutation?

YES

NO

Deletion

Like before, draw the mutation on board and have students visualize/draw out how this will affect protein synthesis. 

The deletion of a single nucleotide at this position shifts the reading frame and results in "wrong" amino acids and a longer polypeptide 

1. what happened to the reading frame? 

All nucleotides downstream of a frameshift mutation will be improperly grouped into codons 

unless the frameshift is near the end of the gene, these mutations usually results in completely non-functional proteins 

gene sequence after the deletion is incorrectly read causing different a.a to be coded for. 

Overview 

Induced mutations: are caused by mutagens 

• Factor or agents causing mutations are known as mutagens (physical or chemical) 
  

 

mutagens fall into two general categories: physical and chemical 

Physical Mutagens 

UV radiation: exposure to sunlight can cause melanoma, a form of skin cancer. 

UV radiation causes a chemical reaction between adjacent pyrimidine bases which result in a distortion in the DNA molecule and interferes with replication.  

• a single sunburn doubles a light-skinned person's chances of developing skin cancer 

Teacher: exposure to sunlight can cause melanoma, a form of skin cancer. 

UV radiation causes a chemical reaction between adjacent pymidine bases which result in a distortion in the DNA molecule and interferes with replication. 

UV radiation causes a chemical reaction between adjacent pyrimidine bases which result in a distortion in the DNA molecule and interferes with replication. increases the rate of spontaneous mutations during DNA replication 

Chemical Mutagens 

• a chemical mutant may act by inserting itself into the DNA molecule that causes a nucleotide substitution or a frameshift mutation 
  

most chemical mutagens are carcinogenic- they are associated with one for more forms of cancer 

Cigarette smokes contains many carcinogen(60+), increases mutation rate. 

We often talk about how science processes impact the environment but it is also important to recognize how environmental factors affect our body and health.  It is essential that we make healthy choices(wear sunscreen, avoid smoking) even though harmful mutations may be rare but it is very much possible and as you saw, a simple change in the DNA sequences causes detrimental effect on the functions and structures of proteins. 

In our next activity, you all will get a chance to explore the different diseases caused by these genetic mutations- seeing how a simple change in the DNA sequences causes a dramatic and terrifying consequence on the human body. 

Smoking causes an increase in mutation rate. Smokers are compared to non-smokers

Mutations....

1. Necessary for Evolution: source of genetic variation. 

2. Cause of many diseases and disorders

• Huntington's Disease, Sickle Cell Anemia