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Introduction to Cell Division
Why do we need more cells? Recall: can’t have bigger cells…need more
cells) To grow, repair, develop, reproduce
Introduction to Cell Division How do we get more cells?
Recall: “cells come from pre-existing cells”
Cells divide into two
Introduction to Cell Division
Before cells can divide, what must they do to prepare?
Grow larger
Grow more organelles
Double their DNA
The Life Cycle of a Cell
Interphase This is where cells grow and copy their DNA
(chromosomes) Has 3 parts:
G1 (growth) S (doubling chromosomes) G2 (growth)
Note: in this phase, DNA is in the form of very thin strands called chromatin…hard to see
The Life Cycle of a Cell Mitosis
Phase responsible for splitting cell into 2 exact copies (new cells)
The Life Cycle of a Cell Interphase
Nucleus visible w/ nucleolus can’t see chromosomes DNA doubles; cell grows
Prophase Chromosomes form (coil) Nuclear membrane
disappears Metaphase
Chromosomes line up in the middle (equator) of cell
The Life Cycle of a Cell Anaphase
Sister chromatids separate & migrateaway from each other
Telophase Cell “furrow” or
cell plate appears Nuclei reappear in
each new cell Cytokinesis
Cytoplasm splits to separate cells
The Life Cycle of a CellName the phase:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Quiz
1. Why are the events of Interphase important?
2. In which phase of mitosis do the sister chromatids separate?
3. Why can’t chromosomes be seen in the cell during Interphase?
4. In which phase of mitosis is the nucleus broken down?
5. Why is mitosis needed? (What is its purpose?)
Quiz
6. Where in the cell does photosynthesis take place?
7. What is the purpose of photosynthesis?
8. Where in the cell does cellular respiration occur?
9. What is the purpose of cell respiration?
10. On the cellular level, why do we need to breathe?
DNA Structure
What is the difference between chromosomes, genes, and DNA? Chromosomes are coiled up rods of DNA Genes are sections of DNA that code for
traits
DNA Structure What does DNA look like?
Double helix…2 strands coiled around each other
Backbone is made up of alternating sugar and phosphate groups
Deoxyribose (sugar)
Phosphate
DNA Structure
What does DNA look like? Connection points are
pairs of bases Adenine (A), guanine
(G), cytosine (C), thymine (T)
A always pairs with T C always pairs with G
How does DNA “control”?
The order of bases spells out the plans for “how to build you”.
The bases work in groups of three. This group is called a “DNA triplet”
How does DNA “control”?
How can 4 bases control everything in our cells (and thus everything in an organism?)
The 4 DNA bases are like letters in the alphabet
The DNA triplets are like words
The entire gene is like a sentence
How does DNA get copied?
DNA Replication DNA unwinds New nucleotides bind to old strands The strands coil back up forming 2 instead of
1
DNA Quiz 1. If the green base is
adenine (A), which base is the red?
2. What structure is represented by the blue section?
3. Which structure is represented by the teal section?
DNA Quiz 4. Which part of DNA actually holds the
code?
5. During which phase of the cell cycle does DNA copy itself?
6. Describe how DNA is able to copy itself. Be specific!
7. What is the difference between a chromosome and a gene?
How do we get actual traits from DNA? Our heritable traits are determined by the
proteins that we make (including our enzymes)
Example: a gene in DNA has directions for how to build melanin…melanin gives you your skin coloration
gene protein trait
Rules for Building a Protein
1) DNA cannot leave the nucleus
2) Must have a messenger to get code from DNA & take it to ribosome
3) Proteins are made from amino acids (AA’s)
Both DNA & RNA are needed to build a protein
DNA 2 strands Deoxyribose sugar Thymine (T) binds
with A RNA
1 strand Ribose sugar Uracil (U) binds with
A
Although they are similar there are some important differences:
What types of RNA are there?
mRNA (messenger RNA) - copies the directions from DNA & takes them to the ribosomes
tRNA (transfer RNA) - picks up certain AA’s & brings them to the ribosome for assembly
How does mRNA know how to copy DNA? DNA triplets match up with sets of 3
mRNA bases…called codons
If DNA says this…what will mRNA be? TAC – GGA – CTT – GAT – ACA – ATT AUG – CCU – GAA – CUA – UGU – UAA
How does mRNA know which AA’s to assemble?
tRNA carries a code of 3 letters called an anticodon that pairs up with the codons of mRNA
If mRNA says this…what will the tRNA’s be? AUG – CCU – GAA – CUA – UGU – UAA UAC – GGA – CUU – GAU – ACA - AUU
How does mRNA know which AA’s to assemble?
Each tRNA can only pick up one specific AA
When it matches up with the anticodon, it brings along its AA
If mRNA says this…what will the AA’s be? AUG – CCU – GAA – CUA – UGU – UAA Met – Pro – Glu – Leu – Cys - Stop
Protein Synthesis Transcription (“to copy”)
mRNA goes to nucleus & copies DNA code for one gene
mRNA takes the copy to the ribosome in the cytoplasm
Protein Synthesis Translation (“DNA” to
“protein”)
Ribosome uses mRNA copy to look for certain tRNA’s (ones with correct anticodon)
tRNA’s pick up specific AA’s & bring them to ribosome when they are needed
AA’s are pulled off tRNA’s & attached to the growing protein chain
Gene Mutations Sometimes mutations (errors) occur
Changes in DNA code may be harmful, helpful, or have no effect
If instructions for cell division affected, can lead to cancer (uncontrolled cell growth)
Gene Mutations
May occur in reproductive cells Affects offspring, not
you
…Or in “body cells” Affects you, not
offspring
Gene Mutations Point Mutations
A change in a single DNA base
THE DOG BIT THE CAT THE DOG BIT THE CAR
This may or may not change the protein that is made (some AA’s have more than one code)
Gene Mutations Frameshift Mutations
AA’s shift when a single base is inserted or deleted
THE DOG BIT THE CAT THE DOB ITT HEC AT (deletion)
THE DOQ GBI TTH ECA (insertion)