ap bio ch. 12, cell cycle
TRANSCRIPT
The Cell Cycle & Mitosis
Ch. 12
Main goals for this lecture
1. Distinguish between chromosomes, chromatids, and chromatin
2. Correctly model and identify in pictures each stage of the cell cycle
The Main Ideas
1. Cell division results in 2 genetically identical daughter cells
2. The mitotic phase alternates with interphase in the cell cycle
The unity of life
• All living things reproduce
• Reproduction occurs at the cellular level
The many functions of cell division
• REPRODUCTION: In unicellular organisms - leads to an increase in the size of the population
• In multicellular organisms - – GROWTH: a single fertilized egg (zygote) divides to
form a new organism– REPAIR: Repairs and renews old or damaged cells
Cell Division results in identical daughter cells
• The DNA is copied and divided between the 2 new cells
• Each new cell (daughter) contains an exact copy of the original DNA
• In human cells, there is about 6 feet of DNA to copy and neatly and accurately divide between the 2 new cells!
Quick Think
What is the purpose of mitosis?
DNA• A cell’s genetic information
is called its genome– In bacteria (prokaryotic cells)
it is usually 1 long circular DNA molecule
– In plants, animals, and fungi (eukaryotic cells) is it usually several linear molecules of DNA
Chromosomes• The individual molecules of DNA are
packaged into chromosomes• Each species has a characteristic number of
chromosomes– Humans - 46– Camel 70– Alligator - 32– Chicken - 78– King crab - 208– Corn - 20
Quick Think
Is the complexity of the organisms directly
proportional to the number of chromosomes? Explain
your answer.
Chromosomes• Chromosomes
are made of chromatin– DNA + proteins
• THE DNA PART: Each chromosome is a single long piece of DNA coding for 100s or 1000s of genes
Chromosomes
• THE PROTEIN PART: the proteins help keep the shape of the chromosome and help control the activity of the genes
Quick Think
• So…what’s a chromosome?
• What is it made of?
• What is it’s purpose?
• Where is it found?
• How many do we have?
Chromosomes• When the cell is dividing the DNA is tightly
packed into X-shaped chromosomes• When the cell is not dividing, the DNA is more
loose - just chromatin strands
Quick Think
• How does the appearance of chromatin and chromosomes vary?
• Draw them…?
Getting the DNA ready for cell division
• Before a cell divides, the DNA (chromatin) condenses and folds into a neat, tightly packed chromosome
• Each chromosome is made up of 2 sister chromatids - identical copies of that particular chromosome
Chromosomes
• The 2 sister chromatids are attached with sticky proteins
• The place where they are attached is called the centromere
Quick Think
Distinguish between chromatin,
chromosomes, and chromatids?
Chromosomes• During cell division, the 2 sister
chromatids are pulled apart to opposite ends of the cell and repackaged into new nuclei
• They are now considered individual chromosomes
Mitosis
• The formation of 2 daughter nuclei
• Followed by the division of the cytoplasm and organelles called cytokinesis
Notice! Not 2 new cells. 2 new nuclei.
Mitosis and Interphase
• Mitotic (M) phase - ~10% of a cell’s life
• Interphase - ~90% of a cell’s life
Interphase• During this time
the cell:– grows– produces proteins
& organelles – copies its
chromosomes– Prepares for cell
division
Interphase• 3 phases:
– G1 phase = first gap• Cell is making proteins and
organelles
– S phase = synthesis• Cell is making proteins and
organelles• DNA IS COPIED
– G2 phase = second gap• Cell is making proteins and
organelles
Mitosis• 5 subphases:
– Prophase– Prometaphase– Metaphase– Anaphase– Telophase
What happens in each phase
• At the end of interphase:– DNA has been copied– DNA not in chromosomes yet– Nucleus intact– The centrosome (an organelle
that helps organize the mitotic spindle fibers) replicates
What happens in each phase• Prophase:
– Chromosomes now tightly coiled– Sister chromatids joined together– Nucleoli disappear– Mitotic spindle begins to form
What happens in each phase• Prometaphase:
– Nuclear membrane breaks up– Microtubles from spindle start to connect with
chromosomes– Each sister chromatid has a kinetochore protein in
the centromere where the spindle fiber attaches
• What is the primary difference between prophase and prometaphase?
What happens in each phase
• Metaphase:– The spindle fibers push
the sister chromatids until they are all lined up at the metaphase plate (the middle of the cell)
What happens in each phase
• Anaphase:– The sister chromatids are pulled apart by
the spindle fibers
What happens in each phase• Telophase:
– New daughter nuclei begin to form around each set of chromosomes
– Chromosomes start to unwind
Quick Think
Explain what happens to the chromosomes
during mitosis
What happens in each phase
• Cytokinesis:– Division of the
cytoplasm– In animal cells, the
two new cells “pinch” apart
– In plant cells, a new cell wall forms between the 2 new daughter cells
What phase is this cell in?
Mitosis Modeling
• One chromosome before the DNA has been copied
Mitosis Modeling
• 2 chromosomes AFTER the DNA has been copied
Mitosis Modeling
• 1 sister chromatid
Mitosis Modeling
• Centromere
Mitosis Modeling
• Interphase – G1
Mitosis Modeling
• Interphase – S
Mitosis Modeling
• Interphase – G2
Mitosis Modeling
• Prophase
Mitosis Modeling
• Prometaphase
Mitosis Modeling
• Metaphse
Mitosis Modeling
• Anaphase
Mitosis Modeling
• Telophase
Mitosis Modeling
• Cytokinesis
Chromosome Challenge!
• With your chromosomes….show me:
• Metaphase
Chromosome Challenge!
• With your chromosomes….show me:
• Early Anaphase
Chromosome Challenge!
• With your chromosomes….show me:
• Late Anaphase
Chromosome Challenge!
• With your chromosomes….show me:
• End of Telophase
Chromosome Challenge!
• With your chromosomes….show me:
• A cell before it has copied the DNA
Chromosome Challenge!
• With your chromosomes…show me:
• All four stages with the people in your row…in order