The DNA Connection

Pages 107-112Pages 107-112

Key ConceptsKey Concepts::

1.1. What forms the genetic code?What forms the genetic code?

2.2. How does a cell produce How does a cell produce proteins?proteins?

3.3. How can mutations effect an How can mutations effect an organism?organism?

Introduction

• The young, white, ring-tailed lemur was born in a forest in Madagascar.

• White lemurs are extremely rare.

• Why was this lemur born with such an uncommon phenotype?

• To answer this question, you need to know how the genes on the chromosome control an organism’s traits.

The Genetic Code

• A review:– Chromosomes are made up of DNA– A DNA molecule is made up of four

nitrogen bases: A, T, C and G– A gene is a specific section on the

DNA molecule that codes for a protein

A single gene could contain several hundred to a million or more bases.

The Order of the Bases are Important

• The order of the bases determines exactly what protein will be made.

• Every 3 letters (codon) codes for an amino acid.

• Chains of amino acids build a protein.

Amino acids are like pearls on a necklace. Pearls are stranded together to form a necklace. Amino acids are stranded together to form a whole protein.

So, how does the cell make proteins?

• The process is called PROTEIN SYNTHESIS.– The cell uses the information from a gene

on a chromosome to make a protein.– Happens on a ribosome in the cytoplasm

• Remember – the ribosome is known as the “Protein Factory.” This is why.

Ribosomes

Protein Synthesis requires DNA and RNA to work together.

• What is RNA?– The “messenger” that carries the code

from DNA out to the cytoplasm.

DNA

RNA

How Are DNA and RNA Different?

1. Number of strands- DNA is double-stranded (known as the

“Double Helix”), while RNA is made up of only one strand

2. Type of sugar- The sugar in DNA is called deoxyribose, while the sugar is RNA is called ribose

3. Nitrogen Bases- DNA is made up of A, T, C, and G, while RNA is made up of A, U, C, and G. Thymine is replaced with URACIL.

Types of RNA

• Messenger RNA (mRNA)– Job: copies the

code from DNA in the nucleus and carries it out to the cytoplasm

• Transfer RNA (tRNA)– Job: carries the

amino acids to a ribosome to form a growing protein.

A waitress copies down the order from the customer. Just like mRNA copies down the code from DNA.

The chef puts together all the ingredients to build a meal. Just like tRNA puts all the amino acids together to build a protein.

How it all Works.

• STEP 1 – Messenger RNA is Made• STEP 2 – Messenger RNA Attaches

to a Ribosome• STEP 3 – Transfer RNA Attaches to

messenger RNA• STEP 4 – The Protein is Complete

STEP 1• mRNA is

made– DNA unzips– mRNA is

made when bases match up to the DNA strand. (U matches up with A)

Step 2

• mRNA attaches to a ribosome– mRNA exits

nucleus and enters the cytoplasm

– The mRNA moves along the ribosome and every 3-letter code is read. (called a CODON)

Step 3• tRNA attaches

to mRNA– tRNA carries

over an amino acid. It matches up to the codon with an anti-codon.

– The protein chain grows with each amino acid.

Step 4

• The protein is done.– The ribosome

reaches a STOP codon.

– The protein is released out to the cell to do its job. Proteins can be short or very

long (100’s or 1000’s of amino acids).

Here’s how the whole process works

http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html

What happens if the wrong protein is made?

• Mutations occur– Any change that occurs in a gene or a

chromosome.

• Can occur randomly (naturally)

• Can be deliberately caused in the laboratory by scientists

• Can be inherited

• Are not always harmful

Types of Mutations• Inherited

• From mutations found in parent’s sex cells

• Acquired

• Changes in body cells during the lifetime of a person

ALBINOS

• Little or no pigmentation in the eyes, skin, and hair.

• Inherited an altered copy of a gene that does not work correctly.

• The altered gene does not allow the body to make the usual amounts of a pigment called "melanin".

• True albinos have pink eyes and skin.

Mutations can be helpful

• Mutations in potatoes causes a new variety to form.

• These Katahdin potatoes are resistant to some diseases that attack other varieties of potatoes. They also look and taste better than other potatoes.