DNA

Unit 3a: SUMMATIVE ASSESSMENTS (large grades)

• ✔ P: DNA Model
• Q: DNA Quiz
• P: Pigeonetics Game
• P: Dragon Breeding Activity
• L: Fast Plant Lab Report
• Q: Genetics Quiz
• P: Controversial Topics in Genetics Presentation

How Does DNA Work?

Part 2:

• How/why does DNA copy itself?
• What is a protein?
• How does DNA help make proteins?

How does DNA copy itself? REPLICATION --> new cell

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Before a cell divides, it makes a copy of its genetic information.

The pairing of bases allows the cell to replicate, or make copies of, DNA.

When DNA replicates

• the double helix splits in the middle
• the pairs of bases separate
• unpaired bases attract new complementary bases
• builds a new complementary strand of nucleotides on each side of the split
• two DNA molecules are formed

Half of each one, that is, one strand, comes from the original molecule. The other strand is built from new nucleotides.

VIDEO

What is a protein?

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• A gene usually contains instructions for making one specific protein.
• Proteins act as chemical messengers for many of the activities in cells.
• Proteins help determine traits.
• The order of bases in DNA is a code.
• The code tells how to make proteins.
• A group of three DNA bases acts as a code for one amino acid.
• For example, the group of DNA bases CAA stand for the amino acid valine.
• Proteins are made from looooooong strings of amino acids.

How does DNA help make proteins?

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RNA, or ribonucleic acid, is a chemical that helps DNA make proteins.

• RNA is similar to DNA but it is only one strand - Amoeba Sisters Video
• One difference between DNA and RNA is that RNA contains the base uracil instead of thymine.
• Uracil is often referred to as U.
• TRANSCRIPTION --> It is a temporary copy of part of a DNA strand.
• TRANSLATION --> Ribosomes “read” the copy and translates it to create amino acids.
• Long strings of amino acids are proteins.
• THE WHOLE PROCESS HERE

What If There are Mistakes

Part 3:

• What happens when there is an error in replicating? (Lots)
• What happens when there is an error in transcription or translation? (Not as much!)

What happens if a gene changes? --“Who Cares?”

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Read this sentence: “Put the book on the desk.” Does it make sense?

What about this sentence: “Rut the zook in the tesk.”?

Changing only a few letters in a sentence can change what the

sentence means.

It can even keep the sentence from making any sense at all!

Even small changes in a DNA sequence can affect the protein

that the DNA codes for.

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A change in the nucleotide-base sequence of DNA is called a mutation.

Some mutations happen because of mistakes when DNA is copied. Other mutations happen when something in the environment damages DNA. Things that can cause mutations are called mutagens. Examples of mutagens include X-rays and ultraviolet radiation.

Some mutations produce new traits that can help an organism survive. For example, a mutation might allow an organism to survive with less water. If there is a drought, the organism will be more likely to survive.

Some mutations produce traits that make an organism less likely to survive. For example, a mutation might make an animal a brighter color. This might make the animal easier for predators to find.

Some mutations are neither helpful nor harmful.

Cells make proteins that can find and fix mutations. However, not all mutations can be fixed. If a mutation happens in egg or sperm cells, the changed gene can be passed from one generation to the next.

3 Types of Mutations

Usually More harmful FRAMESHIFT:

• Insertion --- a base is added
• Deletion --- a base is omitted

Often Less Harmful POINT:

• Substitution --- a base is switched
• *If it changes the amino acid, it’s called a MISSENSE mutation
• *If it does not change the amino acid, it’s called a SILENT mutation
• *If it changes the amino acid to a “stop,” it’s called a NONSENSE mutation

Insertion

Deletion

Substitution

Examples of Mutations

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• Most are neutral
• Eye color
• Birthmarks
• Some are harmful
• Sickle Cell Anemia
• Cystic Fibrosis
• Some are beneficial
• Heterozygous Sickle Cell to Malaria
• Immunity to HIV

Other Mutations

• Some mutations cause serious diseases like Cri-du-chat syndrome
• Deletion of material on 5th chromosome
• This is a mutation that causes babies to be severely mentally impaired and have many health issues.
• Down’s Syndrome
• Chromosome 21 does not separate correctly.
• 47 chromosomes instead of 46.
• Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of intelligence.

Other Mutations

• XYY Syndrome
• Normal male traits
• Often tall and thin
• Associated with antisocial and behavioral problems
• Increased rate of ADHD and autism
• XXX -- Trisomy X
• Female
• Little or no visible differences
• Tall stature
• Learning disabilities
• Increased rate of ADHD

Good mutations

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• Sometimes, very, very rarely, a mutation can be good.
• One example of a good mutation is antibiotic resistance in bacteria
• Every once in awhile (1 in a few million or billion) a bacteria will be resistant to antibiotics. This is really good for that one cell (no so good for us humans!)

How Do Mutations Get Passed On?

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• Not all mutations get passed to offspring
• This is why a person with skin cancer will not automatically have children with skin cancer
• The only way for a mutation to be passed on is if that mutation occurs in the sex cells

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