Molecular GeneticsMolecular Genetics

There’s Two Critical Functions a Cell must Perform during its Lifetime.

• 1. A Cell must divide (reproduce) and have some way to ensure that each of the new daughter cell is complete and somehow receives the information it will need to

perform its life functions. • 2. Once a cell has inherited the

information it needs from the mother cell, it has to use that information to perform a job…. And that job is to make ProteinsProteins.

TraitsTraits• So…… why do some humans have blue eyes, some green eyes, some brown eyes?

• Why do spiders have 8 legs?

• Why does a tree have white bark?

• We know how traits are passed from one generation to the next, thanks to Mendel.

• We know some traits are dominate, some are recessive, some are sex-linked, etc…

The 3 factors which determine the traits of a organism are:

• 1. The absence or presence of a particular protein... determined by the absence or

presence of an enzyme (these enzymes build the structural proteins). These enzymes are

designed by the DNA. • 2. The genes (DNA) the organism inherits

from its parents.• 3. The environment... amount and type of

living conditions, food, light, etc...an organism has its designed genetic potential

but might fail to obtain this potential because environmental conditions are inadequate.

• But, what actually tells your cells how to build you?, or a tree cell to make a root or a

leaf?, or a jellyfish cell to make a tentacle?…. What is this set

of instructions?

The answer of course is

DNADNA

Actually, there’s two types of Nucleic Acids DNADNA and RNARNA…. More about RNA later.

DNA instructs the cell’s DNA instructs the cell’s ribosomesribosomes to build the proteins to build the proteins which are used to make all living organisms.which are used to make all living organisms.

The Location of DNA• In Prokaryotes organisms without a

nucleus, or any membrane-bound organelle, DNA is

found near the center of the cell in an area

called the “Nucleoid”.

• In Eukaryotes the DNA is found in the

“Nucleus”.

Do You Remember?

• Carbohydrates are made of sugarssugars.

• Lipids (Fats) are made of fatty acidsfatty acids.

• Proteins and Enzymes, which are Proteins, are made of Amino AcidsAmino Acids.

• Well…DNA and RNA are made of NucleotidesNucleotides.

The Structure of DNADeoxyriboNucleic Acid

• DNA is a polymer composed of DNA Nucleotides.

Each “Nucleotide” is made Each “Nucleotide” is made up of 3 components:up of 3 components:

1.1. A phosphate groupA phosphate group

2.2. A sugar – the sugar in A sugar – the sugar in DNA is Deoxyribose.DNA is Deoxyribose.

3.3. A Nitrogenous BaseA Nitrogenous Base

Held Together byHeld Together by

““Covalent Bonds.” These Covalent Bonds.” These bonds are strong…. You bonds are strong…. You wouldn’t want your DNA wouldn’t want your DNA

falling apartfalling apart

This is how I draw a Nucleotide

P

S B

Covalent Bonds

A NucleotideThe Phosphate Group is the

same as the phosphates used to make ATP…. You do remember ATP don’t

you?

The Sugar in DNA is Deoxyribose and is a 5

carbon ring sugar.

This Nitrogenous Base is Adenine, it is one of 4 Nitrogenous Bases…..

Nucleotides are Identified by their Nitrogenous Base.

The 4 Nucleotides are:

Adenine

ThymineCytosine

Guanine

Cytosine and Thymine are Pyrimidines. They have only one Carbon Ring.

Adenine and Guanine are Purines. They have two Carbon Rings.

The overall structure of DNA is referred to as a “Double Helix”

(Double Strand)

the symbol 5’ - means 5 prime

the symbol 3’ - means 3 prime

* the symbols 5’ and 3’ will become important to you later

One Helix the other Helix

The Nitrogenous Bases are PairedAdenine always bonds with Thymine

orA T

The Nitrogenous Bases, Adenine and Thymine, are held together by 2 Weak Hydrogen Bonds

The Nitrogenous Bases are PairedGuanine always bonds with Cytosine

orG C

The Nitrogenous Bases, Guanine and Cytosine, are held together by 3 Weak Hydrogen Bonds

Look at the Base PairsAlways A T, G C

DNA has Two Different Types of BondsDNA has Two Different Types of Bonds

• 1. Strong Covalent Bonds, which are found between the Phosphate Groups and the

Nitrogenous Bases…. These strong bonds prevent DNA from coming apart…. It’s bad if

your DNA falls apart.

• 2. Weak Hydrogen Bonds between the Nitrogenous Base Pairs… these weak bonds

allow DNA to “Unzip” (come apart) when it needs to self-replicate (make a copy of itself).

Replication(The Process by which DNA makes a copy of itself)

When a Mother Cell divides, producing 2 Daughter Cells, each of the new daughter cells must receive the information (DNA) it will need to perform its life functions. As a

result of Replication, the Mother cell copies its DNA and gives an exact copy to each resulting Daughter cell. This ensures

that the Daughter cells will have the genetic information (DNA) they need to

survive.

Replication occurs in the Nucleus. (that’s where the DNA and necessary enzymes are)

Replication occurs during the “S” Phase of the Replication occurs during the “S” Phase of the Cell Cycle.Cell Cycle.

In order to make DNA cells need nucleotides…where In order to make DNA cells need nucleotides…where do these nucleotides come from?do these nucleotides come from?

• Animals get Nucleotides by eating cells, either plant or animal. The DNA is broken down into nucleotides which animals can

then reassemble into DNA.

In Plants, compounds such as caffeine, nicotine, rubber, amino acids, which are

needed for proteins, and nucleotides, which are needed to make DNA and RNA are

produced during Respiration.Respiration involves at least 50 different steps.

Each step in the break-up of sugars results in different compounds.

The Process of Replication

Replication takes place in the 5’ to 3’ direction

Step 1. Helicase unzips the DNA

Step 2. DNA Polymerase attaches DNA nucleotides to the

single DNA strand.

Step 3. DNA ligase glues the DNA back together by forming

chemical bonds.