Unit V – Genetics & Heredity Cell Cycle & Mitosis The Cell Cycle & DNA The Story of the Nucleus

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 Cell Cycle

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 Prophase Metaphase 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 Telophase Cytokinesis Sister chromatids separate & migrate away 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 Cell Name 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

DNA Structure

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?

Part 3 – Protein Synthesis The Story of the Ribosome Unit IV – Cell Function Part 3 – Protein Synthesis The Story of the Ribosome

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 DNA cannot leave the nucleus Must have a messenger to get code from DNA & take it to ribosome Proteins are made from amino acids (AA’s)

Both DNA & RNA are needed to build a protein Although they are similar there are some important differences: DNA 2 strands Deoxyribose sugar Thymine (T) binds with A RNA 1 strand Ribose sugar Uracil (U) binds with A

RNA How does RNA differ from DNA? 1 strand U not T ribose

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

Use a chart to find order of AA’s: Which AA is: CGU Arg AUC Iso

Use a chart to find order of AA’s: Which AA is: UCA Ser GAG Glu

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

Protein Synthesis Name the process: Transcription Translation

Protein Synthesis Name the parts: DNA mRNA tRNA Amino Acid Protein Ribosome

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 …Or in “body cells” Affects offspring, not you …Or in “body cells” Affects you, not offspring

Gene Mutations Point Mutations THE DOG BIT THE CAT THE DOG BIT THE CAR 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 Point Mutations

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)

Gene Mutations Frameshift Mutations

The End