Structure of DNA

DNA – Structure and

Replication

Objectives:

1.I can describe the structure and function of DNA

2. I can accurately pair nitrogenous bases to
create a complementary strand of DNA

3. I can explain how copies of DNA are made

What is DNA?

DNA – Deoxyribose Nucleic Acid
•Stores Genetic information
•Chromosomes & Genes
•Our blueprints

Multiple Choice

What is the function of DNA?

• Store energy

• Stores Genetic information

• Build things

• powers our brains

What is the relationship between DNA,
Genes and Chromosome?

• The cell contains the nucleus

•The nucleus contains
chromosomes

•Chromosomes are made of
DNA

•DNA are made of genes

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Cell

nucleus
chromosome

Gene

DNA

Multiple Choice

Which is the smallest?

• Nucleus

• Chromosome

• DNA

• gene

The Structure of DNA

•
The DNA molecule consists of two strands that
wind around one another to form a shape known
as a double helix.

Each strand of DNA is made of:

•
phosphate-sugar “backbone”

•
nitrogenous bases

Monomer = nucleotide

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A DNA nucleotide is composed of 3 parts:

1.Phosphate

2.Sugar

3.Nitrogenous base

These four bases are:

– adenine (A)

– cytosine (C)

– guanine (G)

– thymine (T)

Multiple Select

Select the 3 parts of a nucleotide

• phosphate

• sugar

• nitrogenous base

• gene

Complementary strands

The two strands of DNA
are complementary of
each other

Chargaff’s rule:
A - T

Apples in the tree

Cars in Garage

C - G

Multiple Choice

Adenine (A) matches with ____

• A

• T

• C

• G

Multiple Choice

C (Cytosine) matches with ___

• A

• T

• C

• G

Multiple Choice

If I have AATGC, the complementary strand would be

• TTACG

• CCGAT

• AATGC

• ATGCA

DNA Replication

What is DNA replication?
DNA replication is the process where a
copy of DNA is made

Why would DNA need to replicate?

- To make new cells

- When a new cell is made, the new cell

must have the same DNA as the old
cell

Multiple Choice

What does replication mean?

• to make a copy

• to make a new cell

• to make proteins

• to make energy

When an organism grows its cells divide by MITOSIS. During
this process the DNA needs to be copied and transferred to the
new daughter cell. The process of DNA replication can be
broken down into 3 steps.

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Parent
DNA

DNA for
daughter
cells

STEP 1

1. DNAunzips

• An enzyme named DNA helicase breaks the bonds between

the bases.

• As the DNA unwinds it exposes the base pairs, creating a

replication fork.

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STEP 2

• The DNA that is unzipped then creates a complimentaryDNA

strands using the existing DNA as a template.

• DNA polymerasecreates the new strand by adding

complementary nucleotide bases to the template strand.

TEMPLATE:
G A C T G A C T G A C

DNA polymerase

C

T

G
Complimentary STRAND

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Template STRAND

Complimentary bases

DNA Polymerase has successfully created the new strands, that
match the bases in the original strand.

• The DNA then zips itself up.

• The cell now has an exact copy of its DNA and is ready to

divide to produce a new cell.

TEMPLATE STRAND
G A C T G A C T G A C
C T G A C T G A C T G
NEW STRAND

This DNA is identical to the
original parent DNA.

STEP 3

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New strand

Original Template strand

DNA zips up

Summary

Step 1. The DNA unzips

Step 2: DNA polymerase is used to
create a complimentary strand to
the original strand.

Step 3: The complementary strand
and original strand zip together,
forming DNA that is identical to the
parent DNA

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1

2

3

This is known as semiconservative replication

One old & one new strand

Parent DNA

Daughter

DNA

Reorder

Place the steps of DNA replication in order with 1 being the first step and 3 being the last step

• DNA unzips with the help of DNA helicase

• DNA polymerase makes a complementary strand of DNA

• DNA zips itself up and now there are two identical strands of DNA

1

2

3

• 1
• 2
• 3

Multiple Choice

Why is DNA replication considered semi-conservative?

• It's the far right

• There's one old and one new strand in the new DNA

• The new copy of the DNA is made of two new strands of DNA