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Biology STAAR Review #2
• DNA / RNA / Protein
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Replication
Transcription
Translation
Mutations
• Cell cycle
• Mitosis
• Meiosis
The Genetic Code: DNA – code for all life – in all cells
DNA coils to form Chromosomes
A Gene is a section of DNA
Genetic info is encoded in sequence of base triplets, called codons
Virtually all organisms share the same genetic code
“unity of life”
Organism’s genotype is carried in its sequence of bases
DNA – nucleic acid
long chains of nucleotides
Nucleotide: 3 parts
Phosphate
Sugar
Nitrogen
Base
G, C, A , T
• DNA –
• double strand – twisted ladder or double helix
• Hydrogen bonds between bases hold strands together:
• A with T and C with G
Hydrogen bond
Ribbon model
Partial chemical structure
Computer model
• RNA is also a nucleic acid
– different sugar, ribose
– U instead of T
– Single strand
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
DNA
Both
RNA
Nucleic acid
Double Strand
Nucleotides
Single Strand
Thymine
Nitrogen bases
Uracil
Sugar = Deoxyribose
Sugar
Sugar = Ribose
Controls heredity
Phosphate
Controls protein
synthesis
Replicated before
cell division
Leaves nucleus
Single strand
Nucleotides
Uracil
Thymine
Phosphate
Replicated before cell division
Controls protein synthesis
Sugar
Sugar=deoxyribose
Nucleic acid
Double strand
Leaves nucleus
Controls heredity
Sugar=ribose
Nitrogen bases
Replication: DNA → DNA
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each strand is a template for a new strand
Occurs in nucleus – before cell division
Produces 2 identical double helixes
Purpose: Cell division, reproduction, growth
Figure 10.4B
mRNA
Transcription: DNA → _____
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One strand serves as template
Occurs in nucleus
Produces single strand
Purpose: transfers genetic code for protein synthesis
Protein
Translation: mRNA → _______
• mRNA leaves nucleus
• Occurs in cytoplasm
• Purpose: protein synthesis
Translation: mRNA → Protein
• The “words” of the DNA “language” – 3 bases called codons
Protein
• Sequence of amino acid chain = ________
Ribosome –
“reads” mRNA
codon
tRNA –
brings matching
amino acid
Amino acids
form chain to build
protein
Codon coding for amino acids
thr
ACG = __________
Notice 3 other codons also code for same amino acid
Transcription and Translation - Recap
Nucleus
Cytoplasm
What is Replication?
DNA → DNA
Where does it happen?
Nucleus
Cell
membrane
Ribosome
Mutations can change the meaning of genes
• Mutations (Gene or chromosomal)
• are changes in the DNA base sequence
• caused by errors:
• in DNA replication
• by mutagens
• environmental: UV radiation, chemicals, carcinogens
• Can be helpful harmful or neutral (silent)
• change of a single DNA nucleotide causes disease
Effect depends on
where mutation occurs
1. type of cell
a. body (somatic)
b. sex cell – passed
to offspring
2. type of mutation
Point – changes only 1
• Substitutions = 1 nucleotide changed
• UGC to UGA
• Inversion= reverse order
• UGC to CGA
Gene Mutations
Frameshift – changes all after
• Insertions = nucleotides added – UGC to UGGC
• Deletions = nucleotides deleted – UGC to UC
Chromosomal Mutations – large chunks affected

Deletion - (whole or part deleted)

Insertion - (additional part added)

Duplication - (extra copies of parts)

Inversion - (reverses parts of chromosomes)

Translocation - (parts break off and relocate)
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The Cell Cycle
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Five Phases of the Cell Cycle
G1 - primary growth phase
S – synthesis; DNA replicated
G2 - secondary growth phase
Collectively
these 3 stages
are called
Interphase
M - mitosis
C - cytokinesis
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Interphase - G1 Stage
1st growth stage after cell division
Cells mature by making more cytoplasm &
organelles
Cell carries on its normal metabolic
activities
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Interphase – S Stage
Synthesis stage
DNA is copied or replicated
Two
identical
copies
of DNA
Original
DNA
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Interphase – G2 Stage
2nd Growth Stage
Cell gets ready for division
Copied DNA – checked for mistakes & repaired
All cell structures needed for division are made (e.g.
centrioles)
Both organelles & proteins are synthesized
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Cell
cycle
Grows & makes organelles
& cytoplasm
Doubles
DNA
Checks & repairs
DNA errors
Mitosis:
Identical Daughter Cells
Two
identical
daughter
cells
Parent Cell
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Mitosis: Cell Division
 Used for growth and repair
 Produce two new cells
identical to the original cell
 Cells are diploid (2n)
Chromosomes during Metaphase
of mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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Mitosis
4 stages:
1. Prophase:
The Centrioles begin to move apart.
Chromosomes thicken
The Nuclear membrane disappears
2. Metaphase:
The centrioles are at the “poles” of the cell
The chromosomes line up in the middle of the
nucleus
3. Anaphase:
The Chromosomes are pulled toward the
centrioles by spindle fibers
4. Telophase:
The nucleus begins to reform and the cell begins
to split - cytokinesis
Four Mitotic Stages
What are stages?
Prophase
Metaphase
Anaphase
Telophase
2
1
3
4
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Name the Stages of Mitosis:
Early prophase
Early Anaphase
Metaphase
Interphase
Late Prophase
Late telophase,
Advanced cytokinesis
Early Telophase,
Begin cytokinesis
Mid-Prophase
Late Anaphase
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Identify the Stages
?
Early, Middle, & Late Prophase
?
?
Metaphase
Late Prophase
Anaphase
?
?
Late Anaphase
?
Cytokinesis
?
Telophase
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Cell Division
Cells divide for two reasons.
1. To create copies - Mitosis
2. To create sex cells (gametes) - Meiosis
sperm
egg
Mitosis: Identical Daughter Cells
Mother cell:
2 chromosomes
Daughter cells:
2 chromosomes
Chromosome number the same, but cells smaller
than parent cell
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Meiosis:
The process of creating haploid sex
cells called Gametes
Gamete - sperm or egg
Has two phases of “Mitosis-like
stages”
End result: Half the genetic material
For humans: cell with 46 chromosomes
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forms cells with ___
Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right
number!
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Comparison of Divisions
Mitosis
Meiosis
Number of
divisions
1
2
Number of
daughter cells
2
4
Yes
No
Genetically
identical?
Chromosome #
Where
Same as parent
Somatic cells
body cells
When
Whole life
Role
Growth and
repair
Half of parent
Germ cells
Ovaries / testes
At sexual maturity
Sexual reproduction
Gametes (egg/sperm)
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