DNAThe molecule of life, proteins and heredity

What is DNA?

DNA is a complex macromolecule that contains the genetic information that act as blueprints for making all the components of a cell

It contains the complete instructions for making all the proteins for an organism

Every part of an organism contains proteins, and their shape and functions determine what an organism looks like, what actions it does, what it can eat, even how it thinks!

DNA

Acts as a long-term storage molecule for information that codes all organisms

DNA is composed of long strings of nucleotides bound together A Nucleotide has 3 parts▪ 1. A simple sugar (deoxyribose)▪ 2. A phosphate group▪ 3. A nitrogenous base

Nitrogenous bases in DNA

There are 4 different nitrogenous bases that found in DNA: 1. Adenine (A) 2. Guanine (G) 3. Thymine (T) 4. Cytosine (C)

All the information of DNA is stored in the pattern of these bases in the DNA strand

Base Pairing

DNA bases pair up with each other, this leads to 2 complementing strands

Adenine bonds to Thymine (A-T) Guanine bonds to Cytosine (G-C)

DNA structure

The long strands of nucleotides pairing with each other lead to a ladder like structure called a double helix

The nitrogen bases form the zipper like middle and the phosphate/sugar group of the nucleotide serve as the backbone

Order matters

If you break down any organism to its DNA they all have the same bases of A, T, G and C.

However the order these bases are arranged in is what separates snails from frogs and from humans etc.

Humans have just over 3 billion base pairs!

Recall…

DNA is replicated during interphase before mitosis and meiosis

Is it important that the DNA that is replicated is identical?

DNA replication

Starts when the 2 strands of DNA separate

Each strand serves as a template for incoming bases Since A only pairs

with T and G only pairs with C

DNA replication

So nucleotide bases will come in and pair with the appropriate counterpart and begin forming 2 strands of identical DNA

Enzymes control Replication

There are Many enzymes which allow for DNA replication

1. DNA Polymerase2. Helicase3. Primase4. DNA ligase

DNA Polymerase

This enzyme is what finds and attaches the complementary base to the forming strand of DNA

It can only attach bases in a 5’ to 3’ direction

Leading vs Lagging strands Because DNA polymerase can only

add bases in a 5’ to 3’ direction it forms both leading and lagging strands

The leading strand can start and continue along as the DNA is unwound

The lagging strand must replicate in chunks, called okazaki fragments, because the DNA polymerase must run in the opposite direction of the unwinding

DNA proofreading

DNA polymerase is extremely accurate, however it does also fix mistakes to increase the fidelity of DNA

This means that DNA replication is extremely accurate!

DNA Helicase

This enzyme is responsible for opening up the strands of DNA to allow replication to begin

DNA Primase

Is an enzyme that binds initially to allow DNA polymerase to bind the strand and begin matching base pairs

DNA Ligase

Is an enzyme that comes in and seals the nicks left in the lagging strand

Replication Practice

Complete the complementary strand of DNA if the template strand is

ATTCGTTCGTAGC