unit 7 - dna structure and replication
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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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