1

PROTEIN PROTEIN SYNTHESISSYNTHESIS

and Mutations…and Mutations…

2

TranscriptionTranscription

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Prokaryotic CellProkaryotic Cell

DNA DNA RNA RNA ProteinProtein

3

DNA DNA RNA RNA ProteinProteinSo, DNA is like a So, DNA is like a

recipe…recipe…

RNA is like a copy of RNA is like a copy of the recipe… the recipe…

Protein is what is Protein is what is being made…the being made…the

cookies!cookies!

4

What if the recipe for What if the recipe for Grandma’s famous Grandma’s famous cookies called for 1 cookies called for 1 teaspoon of salt…teaspoon of salt…

But when I copied the But when I copied the recipe, I wrote 1 cup of recipe, I wrote 1 cup of

salt?salt?

5

So, if the recipe gets So, if the recipe gets changed…the cookies changed…the cookies

will get changed.will get changed.

It’s the same with It’s the same with DNA!DNA!

If the original DNA is If the original DNA is changed, the protein changed, the protein

may be changed!may be changed!

6

Is a change in the Is a change in the recipe, always a bad recipe, always a bad

thing?thing?

Some DNA mutations Some DNA mutations are beneficial!are beneficial!

Remember, DNA codes Remember, DNA codes for proteins that for proteins that determine traits!determine traits!

7

What is a MUTATION?What is a MUTATION?

A change in DNAA change in DNA

8

What causes What causes MUTATIONS?MUTATIONS?

They happen all the They happen all the time when DNA is time when DNA is

copied! Thankfully, copied! Thankfully, DNA polymerase DNA polymerase

proofreads and fixes proofreads and fixes these changes.these changes.

9

What causes What causes MUTATIONS?MUTATIONS?

Mutagens are things Mutagens are things that cause mutation.that cause mutation.

Examples of mutagens…

• UV light (from sun or tanning beds)

• X-ray exposure

• Radioactivity

• Chemicals (ex: cigarette smoke)

10

11

We will look at 3 types We will look at 3 types of DNA mutation.of DNA mutation.

Remember, mutations Remember, mutations are changes to DNA…are changes to DNA…that can then affect that can then affect

RNA…which can then RNA…which can then affect a protein!affect a protein!

12

Look at the Look at the following following sentence.sentence.

13

THE CAT ATE THE RATTHE CAT ATE THE RAT

Now look at the next Now look at the next sentence…do you see sentence…do you see

what’s been changed? what’s been changed? SHHHH! Don’t tell!SHHHH! Don’t tell!

THE BAT ATE THE RATTHE BAT ATE THE RAT

14

THE THE CCAT ATE THE RATAT ATE THE RAT

THE THE BBAT ATE THE RATAT ATE THE RAT

15

1. SUBSTITUTION 1. SUBSTITUTION

•Change 1 DNA Change 1 DNA nucleotidenucleotide

•Can change 1 amino Can change 1 amino acid in the proteinacid in the protein

•May have no affectMay have no affect

DNA: ACA

mRNA:

AA:

DNA: ACC

mRNA:

AA:

DNA: ACT

mRNA:

AA:

DNA: ACG

mRNA:

AA:

16

UGUCysteine

UGG

Tryptophan

UGAStop

UGC

Cysteine

What’s the point?

• Because of the repitition of the code, sometimes you can make a substitution and it still codes for the same amino acid. Other times, it changes the amino acid. If it changes it to a “stop”, then that’s a pretty big change

17

18

Look at the Look at the following following sentence.sentence.

19

THE CAT ATE THE RATTHE CAT ATE THE RAT

Now look at the next Now look at the next sentence…do you see sentence…do you see

what’s been changed? what’s been changed? SHHHH! Don’t tell!SHHHH! Don’t tell!

THE CAT TET HER AT THE CAT TET HER AT

20

THE CAT THE CAT AATE THE RATTE THE RAT

THE CAT THE CAT __TET HER AT TET HER AT

21

2. DELETION2. DELETION

•Delete 1 or more DNA Delete 1 or more DNA nucleotidesnucleotides

•Shifts the nucleotides Shifts the nucleotides = a frameshift = a frameshift

mutationmutation•Changes the protein Changes the protein

down from the down from the mutationmutation

22

Look at the Look at the following following sentence.sentence.

23

THE CAT ATE THE RATTHE CAT ATE THE RAT

Now look at the next Now look at the next sentence…do you see sentence…do you see

what’s been changed? what’s been changed? SHHHH! Don’t tell!SHHHH! Don’t tell!

THE CAT TAT ETH ERA THE CAT TAT ETH ERA TT

24

THE CAT ATE THE RATTHE CAT ATE THE RATTHE CAT THE CAT TTAT ETH ERA AT ETH ERA

TT

25

3. INSERTION3. INSERTION

•Add 1 or more DNA Add 1 or more DNA nucleotidesnucleotides

•Shifts the nucleotides Shifts the nucleotides = a frameshift = a frameshift

mutationmutation•Changes the protein Changes the protein

down from the down from the mutationmutation

26

If I spend a lot of time in If I spend a lot of time in the sun and the DNA in one the sun and the DNA in one

of my skin cells gets a of my skin cells gets a mutation…mutation…

I may get skin cancer…I may get skin cancer…

But would/could I pass this But would/could I pass this to a child?to a child?Only mutations in sex Only mutations in sex

cells (egg or sperm) cells (egg or sperm) are passed to are passed to

offspring!offspring!

• That’s why when you have x-rays done, the technicians put a lead drape over your “reproductive zone” – they don’t want to mutate your eggs/sperm!!!

27

Links• Sickle cell anemia:

http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html

• Tay Sacs: http://www.pbs.org/wgbh/nova/programs/ht/qt/2809_qlg_03.html

• Cystic Fibrosis: http://www.pbs.org/wgbh/nova/programs/ht/qt/2809_qlg_03.html

• http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/cftr.shtml

28