UNIT 7 – DNA

STRUCTURE AND

REPLICATIONSTANDARDS H.B.2 & H.B.4

DNA STRUCTURE

DNA: THE MOLECULE OF

HEREDITY

Objectives:

You will be able to describe the

molecule and forms of DNA.

You will be able to describe the

difference between DNA, genes,

and chromosomes.

You will be able to determine

what makes us different from

other organisms even though we

all share DNA as genetic code.

You will be able to describe

homologous chromosomes.

WARM-UP #1 – NUCLEIC ACIDS

REVIEW

1. What elements are found in nucleic acids?

C, H, N, O, P

2. Nucleic acids are polymers made of many monomers. What is

the name of the monomer for nucleic acids?

nucleotide

3. What are the 3 parts of the monomers for nucleic acids?

DNA STRUCTURE AND POGIL

REVIEW Get out the DNA Structure and Replication POGIL Worksheet and be ready to

review answers based off Model 1:

DNA: THE “BASE”ICS

DNA –

Deoxyribonucleic Acid

Type of nucleic acid

Made of nucleotides

Unit of heredity in all

living things

Contains the information for

making proteins

Only in Nucleus of the

cell

DNA: THE “BASE”ICS

Watson & Crick – determined

DNA was a “Double Helix”

structure (twisted ladder)

DNA: THE “BASE”ICS

Nucleotide

Sugar (Deoxyribose)

Phosphate

Nitrogen Base

Adenine (A)

Thymine (T)

Guanine (G)

Cytosine (C)

4 NITROGEN BASES Adenine & Guanine = Purines (2 rings in structure)

Cytosine & Thymine = Pyrimidines (1 ring in structure)

Hint to

remember…Look at

the “Y”s !!

Chains (sugar-phosphate backbones) are formed by

joining the sugar of one nucleotide to the phosphate

of the next nucleotide

DNA: THE “BASE”ICS

“Sugar –

Phosphate

Backbone”

DNA: THE “BASE”ICS

Nitrogen bases come off of the sugar (deoxyribose)

Hydrogen bonds hold the bases together to form a pair

Base pairing rules:

A always pairs with T

amount of A always EQUALS amount of T

C always pairs with G

amount of G always EQUALSamount of C

Called complementary bases

Hydrogen Bonds

Hydrogen Bonds

CHECK FOR

UNDERSTANDING1. What is the name for DNA?

2. What information does DNA hold?

3. What are the monomers for DNA?

4. What is the overall structure of DNA called?

5. What are the 3 parts of a nucleotide?

6. What are the 4 nitrogen bases in DNA?

7. What are the base pairing rules?

8. What holds the bases together in a DNA molecule?

What is the complementary strand (opposite

strand) of the DNA below?

A T C G C G

CHECK FOR

UNDERSTANDING

DNA AND

NUCLEOTIDE

SEQUENCES

DNA AND NUCLEOTIDE

SEQUENCES

All organisms have DNA

All DNA is made of the same 4 nucleotide bases

How are we different from dogs, cats, trees, bacteria,

etc?

DNA AND NUCLEOTIDE

SEQUENCES The different ways the nucleotides (A,T,G,C) are

arranged create different proteins

The order/sequence of nucleotides (ATCG) in each chromosome has the info to make a specific protein

Just think…. Ant vs. Tan (same letters but very different things)

The sequence of nucleotides carries different geneticinformation

A-T-T-G-A-C vs. T-C-C-G-A-A

DNA AND NUCLEOTIDE

SEQUENCES

The closer two organisms are related to one

another, the more similar their DNA sequences

Nucleotide sequence of chimp is similar to gorilla, but very

different from a rose

We can use nucleotide sequence to determine

evolutionary relationships among organisms.

Can use nucleotide sequence to determine if 2 people are

related or identify criminals

FORMS OF DNA

FORMS OF DNA IN THE

NUCLEUS

Chromatin – form of

double helical DNA

most of a cell’s life

Uncoiled, relaxed DNA

Not visible with a light

microscope

FORMS OF DNA IN THE

NUCLEUS

Chromosome – form of double helical DNA during

cell division

Tightly coiled (supercoiled)

Visible with a light microscope

FORMS OF DNA IN THE

NUCLEUS

Chromatin Chromosomes

CHECK FOR

UNDERSTANDING

1. What is the structure of a DNA molecule?

2. What are the 2 forms of DNA?

3. What is the difference in a chromosome and

chromatin?

4. Why are we different from other organisms and

other people?

WARM-UP #2 – COMPLEMENTARY

BASE PAIRING

DNA, GENES, AND

CHROMOSOMES

DNA, GENES, CHROMOSOMES Chromosome = supercoiled strand of DNA

A CHROMOSOME IS DNA!

Genes = short segments of DNA that code for a specific protein

A GENE IS DNA…IT IS JUST A PART OF THE ENTIRE DNA STRAND!

Genes are expressed/shown as traits

Example – eye color

Alleles = different forms/variations of a gene

Example – brown eyes, blue eyes, green eyes

HOMOLOGOUS

CHROMOSOMES Homologous chromosomes = pairs of chromosomes

that have the same size, shape, and same types of

genes

Alleles for the genes on homologous chromosomes

don’t have to be the same

HOMOLOGOUS

CHROMOSOMES Humans have 23 pairs of homologous chromosomes

in their body/somatic cells

One chromosome from the pair is from mom and other

chromosome is from dad

HOMOLOGOUS

CHROMOSOMES Chromosome pairs

#’s 1-22 = autosomes

Have genes for all traits except gender/sex determination

Chromosome pair #23 = sex chromosomes

Sex chromosomes = X and Y in mammals

XX = female, XY = male

KARYOTYPES

CHECK FOR

UNDERSTANDING1. How many chromosomes do humans have in their

somatic cells?

2. What are alleles?

3. What are autosomes?

4. What sex chromosomes would a female have?

Male?

REPLICATION

DNA REPLICATION

Objective: You will be able to

explain replication and create a

new strand of DNA through

replication.

DNA REPLICATION

DNA Replication – process of copying DNA

Occurs every time a cell reproduces in mitosis or meiosis

Occurs in the S phase of interphase in the cell cycle

Replication assures that every cell has a complete set of identical genetic info

End result = 2 identical double helices of DNA

Parental DNA is

used as a

“template”

New strand

formed is called a

complement

DNA REPLICATION

Semi-conservative process - produces 2 copies that

each contain one of the original strands and one

entirely new strand

STEPS OF REPLICATION

1. Enzyme (helicase) breaks the weak hydrogen bonds

between nitrogen base pairs and “unzips” the DNA

double helix

2. Each separated strand acts as a template for free

nitrogen bases in the nucleus to join with the open

DNA strand following the base pairing rules

A bonds with T & G bonds with C

DNA polymerase - enzyme that hydrogen bonds the nitrogen

bases together

3. Two new identical strands of DNA are made

After DNA replication,

chromosome looks like a

“X” (called a duplicated

chromosome)

Half of a duplicated

chromosome = sister

chromatid

Centromere = protein

complex holding

together identical sister

chromatids

CHROMOSOMES AFTER

REPLICATION

CHECK FOR

UNDERSTANDING1. What is DNA replication?

2. When does DNA replication happen?

3. Why does DNA replication happen?

4. What is the end result of DNA replication?

5. What “unzips” the DNA molecule in replication?

6. What molecule helps bond the new nucleotides to the DNA template?

7. What do we call the newly made strand (side) of DNA?

Replicate the parent DNA below. Label template and daughter/complementary strands. Circle the TWO daughter DNA molecules.

A - T

T - A

C - G

G - C

A - T

A - T

C - G

C - G

G - C

A - T

T - A

CHECK FOR

UNDERSTANDING

WARM-UP #3 – FORMS OF DNA

LABELING Use the following

terms to label the

picture:

1. Nucleus

2. Double helix

3. Chromatin

4. Chromosome

5. Gene

6. Sister Chromatids

7. Base pairs

8. Centromere

A

B

H

G

F

D

E

C