How is the amino acid sequence determined?

• The mRNA• Each codon is a code for one amino acid

DNA sequence: T A C C G A G A T T C AmRNA sequence: A U G G C U C U A A G Uamino acid sequence: Met -- Ala -- Leu -- Ser

Whole Process Video

Notes on Mutations

LT: Understand the different types of mutations and why some are worse than others.

Mutations

Mutation- a change in the DNA nucleotide sequence

Mutations can cause subtle or dramatic effects on observed traits in individuals

How does your DNA determine your traits?

DNA mRNA protein Observed trait

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Remember:•Traits are determined by the functions of proteins•Protein function is determined by protein shape•Protein shape is determined by amino acid sequence

Amino Acid sequence determines the 3-D protein shape

• Interactions between amino acids cause folding and bending of the chain

Examples: – positive (+) and negative (-) parts of amino acids are

attracted to each other.– hydrophobic regions are attracted to each other

• Foldinghttp://www.stolaf.edu/people/giannini/flashanimat/proteins/hydrophobic%20force.swf• Structure levelshttp://www.stolaf.edu/people/giannini/flashanimat/proteins/protein structure.swf

Mutations can change the amino acid sequences of proteins

DNA sequence: T A C C G A G A T T C AmRNA sequence: A U G G C U C U A A G Uamino acid sequence: Met -- Ala -- Leu -- Ser

DNA sequence: T A C C G A G A T T C A

mRNA sequence: A U G G C U A U A A G Uamino acid sequence: Met -- Ala -- Iso -- Ser

T

+ -

+

How does this mutation change the amino acid sequence?

(Original)

DNA sequence: A A T G C A T A T G C AmRNA sequence: U U A C G U A U A C G Uamino acid sequence: Leu -- Arg -- Ile -- Arg

(Mutated)

DNA sequence: A A T T C A T A T G C AmRNA sequence: U U A A G U A U A C G Uamino acid sequence: Leu -- Ser -- Ile -- Arg

T G A T T C A

3 types of mutations

T A C C G A G A T T C A

T A C C G A

T A C C G A G A T T C A

Substitution

Insertion

Deletion

TSubstituting one nucleotide for another.

Inserting one or more nucleotides

Deleting one or more nucleotides

Practice

• Complete both sides of the “Mutations practice”. You will learn how some mutations can affect the amino acid sequence of proteins

• Consider how severe of an effect each mutation would have on the ability of the protein to function.

1. Which mutations had the biggest effect on the protein sequence? WHY?

2. Which mutations had the smallest effect on the protein sequence? WHY?

3. Which examples would you predict to have the biggest effects on a trait? WHY?

4. Which examples would you predict to have the smallest effects on a trait? WHY?

T G A T T C A

Different types of mutations happen

T A C C G A G A T T C A

T A C C G A

T A C C G A G A T T C A

Substitution

Insertion

Deletion

T

Frameshift mutations• One or more than one nucleotide can be added

or deleted with insertion and deletion mutations.

• If the number of nucleotides is not a multiple of 3, it is called a frameshift mutation.

1. Why do we call this a frameshift mutation?2. Can substitution mutations cause frameshifts?

Explain why or why not.

Nonsense mutations

• The introduction of a stop codon where it doesn’t belong

• Results in a shorter, unfinished protein

• If a mutation in sperm or egg DNA is not fixed, the new sequence of DNA is passed on to offspring.

• Over generations, more mutations accumulate.

• As a result, differences occur between people’s DNA sequences!

Consequences of mutations…

How much variation in DNA exists between 2 people?

Hemoglobin (beta) gene sequence from person A

How much variation in DNA exists between 2 people?

Hemoglobin (beta) gene sequence from person B

How much variation in DNA exists between 2 people?

• About 1 in every 1,000 nucleotides is different between 2 people

• (0.1% difference means 99.9% identical)

• We have about 3 billion nucleotides in all, so that means there are about 3 million nucleotide differences between 2 people

What is the observed effect of mutations?

• No Effect (think about it: are there 3 million differences between 2 people?)

– Why?1. Some mutations code for the same

amino acid2. Most mutations are in sequences of DNA

between genes.• Variation – there are a variety of traits in a

population.• Genetic disease

Genetic diseases

Many alleles are harmless, but some can cause specific diseases. They can be dominant or recessive. To determine whether a disease is genetic, we trace the family history of a disease by creating a type of family tree called a pedigree.

Environmental Causes of Mutations

• Mutagens - substances that cause mutations (changes in DNA sequence)

– Ex: cigarette smoke, UV light, x-rays, nuclear radiation, BPA, etc.

• Carcinogen – cancer causing substance (mutation in a gene linked with cancer)

Reading pgs. 436-437

3a. In what ways do mutations affect organisms?

b. How can mutations occur?

Changes the message sent by the DNA – can make it so the protein does not function or RARELY makes it function better

Spontaneously, or through MUTAGENS – chemicals or agents that cause mutations in your DNA (cigarette smoke, UV radiation, BPA, etc.)

c. Why can mutations in gametes have a different effect than mutations in nongamete cells?

Nongamete cells do not pass on their instructions to offspring – they only affect the individual. Mutations in gametes will be passed on to offspring.

DNA and Evolution

• We saw in previous chapters that fossils show us how organisms have changed over time.

• We can use DNA to examine patterns of evolution.

DNA and Evolution

• A hemoglobin molecule complex consists of 2 protein chaings – an alpha chain and a beta chain.

• There are 146 amino acids in the beta chain of hemoglobin.

• We are going to examine the beta hemoglobin sequences of 8 different species to try to identify the relationship between these 8 species.

DNA and Evolution

• Count the differences between the sequences for species I and II, I and III, I and IV, etc.

• Make a class list on the board.• How many of the 146 amino acids in the beta

chain of hemoglobin do the two most similar sequences share?

• How many do the two least similar sequences share?

DNA and Evolution

• The first 7 species are primates:• I – Human• II – Chimpanzee (Great Ape)• III – Gorilla (Great Ape)• IV – Common Gibbon (“lesser” Ape)• V – Rhesus Monkey (old world monkey)• VI – Squirrel Monkey (new world monkey)• VII – Ring-tail lemur (Prosimian)

DNA and Evolution

• Which group of primates is least similar to the others? Prosimians are least similar

• Are gorillas more similar to humans, or to chimpanzees?

• Which 2 species have the fewest differences (most similar sequences)? Label them on Tree A in the blanks indicating closest similarity.

• Which third species is most similar to the first 2? Label them on Tree A.

DNA and Evolution

• What position shows the common ancestor of Chimpanzees and Humans?

• Position 4 shows the common ancestor of which species?

• Is the Old World Monkey more closely related to the Gorilla or to the New World Monkey?