Genes and Gene Technology

What do Genes Look Like?

Genes determine the traits of an organism are passed on from one generation to

another located on chromosomes

Chromosomes are made of protein DNA= deoxyribonucleic acid

Pieces of the Puzzle

Supply instructions for cell processes and building cell structures

Be copied each time a cell divides

What a Gene Has to Be Able to Do

DNA is made of only four subunits which are called nucleotides

Each nucleotide consists of a sugar a phosphate a base

Nucleotides are identical except for the base

The Subunits of DNA

Thymine Adenine Guanine Cytosine

They each have a slightly different shape.

The base is usually referred to by the first letters in their names: A, T, G, C.

The Four Bases

In the 1950’s, Erwin Chargraff found that the amount of adenine in DNA always equals the amount of thymine.

Also the amount of guanine always equals the amount of cytosine.

These findings are known as Chargraff’s rules.

Chargraff’s Rules

Rosalind Franklin was able to create images of DNA molecules using a process known as X-ray diffraction.

The images that Franklin created suggested that DNA has a spiral shape.

A Picture of DNA

James Watson and Francis Crick were also investigating the structure of DNA.

Based on Franklin’s image, they concluded that DNA resembles a twisted ladder shape known as a double helix.

They used their DNA model to predict how DNA is copied.

Eureka!

Making Copies of DNA

One side of DNA is complementary to the other.

DNA splits down the middle where the two bases meet.

The bases can be used as a pattern for a new complimentary side.

Incomplete dominance Sometimes one trait is not completely

dominant over another These traits don’t blend together but

each allele has its own degree of influence

More About Traits

Genes Influence Traits Sometimes one gene influences more

than one trait Some traits are the result of several

genes acting together

More About Traits

Importance of Environment

Many things in your environment influence how you grow and develop Healthy diet Exercise

You may have the genes to grow tall but you won’t reach your full potential height without the proper nutrients

More About Traits

List and describe the parts of a nucleotide.

Which bases pair together in a DNA molecule?

If a sample of DNA were found to contain 20 percent cytosine, what % of guanine would be in this sample? Why?

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HOW DNA WORKS

Section 2

DNA is often wound around proteins, coiled into strands, and then bundled up even more. In a cell that has a nucleus, the strands of DNA and proteins are bundled into chromosomes.

A gene consists of a string of nucleotides that give the cell information about how to make a specific trait.

Unraveling DNA

Genes and Proteins

Proteins act as chemical triggers for many of the processes within cells. Proteins help determine traits.

Another type of molecule that helps make proteins is called RNA, or ribonucleic acid. RNA is so similar to DNA that RNA can serve as a temporary copy of a DNA sequence.

The first step in making a protein is to copy one side of the segment of DNA containing a gene. This copy is called messenger RNA (mRNA).

This copy is identical to the original section except instead of copying thymine, the copy has uracil.

After being made, the mRNA moves from the cell’s nucleus into the cytoplasm.

Protein Synthesis: Transcription

Transcription

Protein Synthesis: Translation

The mRna is then fed through a ribosome. The ribosome reads three bases of the mRNA at a time.

These groups of three bases code for a specific amino acid. The groups are called codons.

Transfer RNA (tRNA) delivers amino acids from the cytoplasm to the ribosome

Protein Synthesis: Translation

The amino acids are dropped off at the ribosome.

As more mRNA is fed through the ribosome, tRNA brings more amino acids to drop off. As they are dropped off they join together.

Protein Synthesis: Translation

The ribosome starts reading the mRNA at the START codon. AUG is almost always the START codon, especially for eukaryotes.

Once the ribosome reads the STOP codon, the amino acids that are joined together form the protein that the mRNA was coded to make.

The STOP codons are UAA, UAG, or UGA.

Translation

Changes in Genes

Changes in the number, type, or order of nucleotide bases on a piece of DNA are known as mutations.

Insertion: Base is added that wasn’t in original sequence

Substitution: Base that was in original sequence is replaced by another

Deletion: Base from original sequence is removed

Types of Mutations

Insertion

Deletion

Substitution

There are three possible consequences to changes in DNA: an improved trait, no change, or a harmful trait.

Mutations happen regularly because of random errors when DNA is copied. Any physical or chemical agent that can cause a mutation in DNA is called a mutagen.

Examples: X-rays, UV radiation, asbestos, chemicals in cigarette smoke

Mutations

Mistakes during DNA replication are estimated to occur in 1 of every 10,000 base pairs.

We have built-in DNA checking mechanisms that catch most of these mutations and correct them. The final error rate is as low as 1 in 1 billion.

Mutants Among Us?

Example of Substitution

A mutation, such as a substitution, can be harmful because it may cause a gene to produce the wrong protein.

A simple change in an amino acid can cause a disease such as sickle cell anemia. Sickle cells are not as good at carrying oxygen and also are more likely to cause dangerous blood clots.

Uses of Genetic Knowledge

Scientists can manipulate individual genes within organisms. This kind of manipulation is called genetic engineering.

Your DNA is unique, so it can be used like a fingerprint to identify you. DNA fingerprinting identifies the unique patterns in an individual’s DNA. Its two main uses are identifying evidence in criminal cases and determining whether people are related.

What is the function of the ribosome in protein synthesis?

What are the three types of mutations? What is a mutagen?

Explain the relationship between genes and proteins.

What is a codon?

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