Molecular genetics
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Molecular 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.

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Molecular Genetics

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Molecular genetics l.jpg

Molecular Genetics

There s two critical functions a cell must perform during its lifetime l.jpg

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 Proteins.

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  • 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 l.jpg

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, organism has its designed genetic potential but might fail to obtain this potential because environmental conditions are inadequate.

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  • 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?

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The answer of course is


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

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

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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”.

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Do You Remember?

  • Carbohydrates are made of sugars.

  • Lipids (Fats) are made of fatty acids.

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

  • Well…DNA and RNA are made of Nucleotides.

The structure of dna d eoxyribo n ucleic a cid l.jpg

The Structure of DNADeoxyriboNucleic Acid

  • DNA is a polymer composed of DNA Nucleotides.

Covalent Bonds

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

  • A phosphate group

  • A sugar – the sugar in DNA is Deoxyribose.

  • A Nitrogenous Base

  • Held Together by

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

This is how I draw a Nucleotide



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A Nucleotide

The Phosphate Group is the same as the phosphates used to make ATP…. You do remember ATP don’t you?

This Nitrogenous Base is Adenine, it is one of 4 Nitrogenous Bases….. Nucleotides are Identified by their Nitrogenous Base.

The Sugar in DNA is Deoxyribose and is a 5 carbon ring sugar.

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The 4 Nucleotides are:

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



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



The overall structure of dna is referred to as a double helix l.jpg

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

(Double Strand)

One Helix the other Helix

the symbol 5’ - means 5 prime

the symbol 3’ - means 3 prime

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

The nitrogenous bases are paired adenine always bonds with thymine or a t l.jpg

The Nitrogenous Bases are PairedAdenine always bonds with ThymineorA T

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

The nitrogenous bases are paired guanine always bonds with cytosine or g c l.jpg

The Nitrogenous Bases are PairedGuanine always bonds with CytosineorG C

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

Look at the base pairs always a t g c l.jpg

Look at the Base PairsAlways A T, G C

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DNA 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 l.jpg

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 l.jpg

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

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

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In order to make DNA cells need nucleotides…where 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.

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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.

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