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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?

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STATE STANDARD 4.1, 4.2, AND 4.3

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)

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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 phosphateof 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

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CHECK FOR UNDERSTANDING

1. 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

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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

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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?

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WARM-UP #2 – COMPLEMENTARY BASE PAIRING

STATE STANDARD 4.1, 4.2, AND 4.3

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

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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

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KARYOTYPESCHECK FOR UNDERSTANDING

1. 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?

REPLICATIONDNA REPLICATION

Objective: You will be able to

explain replication and create a

new strand of DNA through

replication.

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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 REPLICATION1. 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 to add 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

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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 UNDERSTANDING

1. 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

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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