The Cell Cycle & DNAThe 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

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

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?

Unit IV – Cell Function

Part 3 – Protein SynthesisThe 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

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:

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 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 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