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Test on DNA, Cell Cycle Gene Expression, Replication, Mitosis, & maybe Mutations 12/11-12/12. Tuesday December 3, 2013. Agenda : Homework Check Discussion: Why Cells Divide, Chromosomes & Preparing for Mitosis: -------------Warm Up- -----------------------------------------------

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tuesday december 3 2013
Test on DNA, Cell Cycle Gene Expression, Replication, Mitosis, & maybe Mutations 12/11-12/12Tuesday December 3, 2013


  • Homework Check
  • Discussion: Why Cells Divide, Chromosomes & Preparing for Mitosis:

-------------Warm Up------------------------------------------------

  • What is DNA replication and what is its goal?

----------HW: ------------

  • Re-read outlines on CH9: Cell cycle, Chromosomes and Mitosis.




Without looking at your notes, what is…















mitosis objective
Mitosis Objective
  • Students will understand the process of The Cell cycle. The students will also be able to demonstrate how the process of Mitosis functions and aides in their life.
the two possible outcomes
The Two Possible Outcomes
  • Upon conception, a sperm fertilizes an egg.
  • From this point, the DNA from dad and mom are joined to give a new organism all the DNA it needs to live.
  • But the size of a fertilized egg is microscopic.
  • How do we, as organisms, get to be the size we are when finally finish growing, from such simple origins?
  • There are two solutions.
  • One way is for that one fertilized cell to keep getting larger and larger.
  • But that would result in a gigantic blob.
  • But are cells big or small? Why?
option two
Option Two
  • The second option, the one that really happens, is we grow as a result of the number of our cells growing.
  • The number of cells grow from the existing cells that are already there.
  • The existing cells split in half, giving birth to 2 identical versions of itself.
  • The growing number of cells each survive independently but work together to give rise to complex multicellular organisms, like humans.
  • This process of cell division is a vital part of development, of healing, of life.
chapter 10 section 1 objectives
Chapter 10 Section 1 Objectives
  • List 3 reasons why cells divide.
  • Describe three levels of structure in the DNA packaging in the nucleus.
  • Explain what are daughter cells and why they are identical to the parent cells.
  • Describe how cells (both prokaryotic and eukaryotic) prepare for division.
  • Gene
  • Chromosome
  • Chromatin
  • Histone
  • Nucleosome
  • Chromatid
  • Centromere
what do these things have in common
What do these things have in common?
  • Human Growth
  • Growth of plant
  • Wound healing
what is cell reproduction
What is Cell Reproduction?
  • As the body of a multicellular organism grows larger, its cells do not just grow large too.
  • Instead, the body grows by increasing the number of the same size cells.
    • An adult human can produce up to around 2 trillion cells per day!
  • This is known as cellular reproduction.
  • Or more commonly, mitosis.
why cells reproduce
Why Cells Reproduce
  • There are three main reasons cells divide:
  • 1. To help tissues and organs grow.
    • We continuously add cells as we grow to get bigger.
  • 2. To replace cells.
    • As old cells die or cells get damaged new cells take their place in order to maintain health.
    • As the cell ages, it continues to grow. When it gets too big it need to be replaced to limit cell size.
  • 3. To repair broken cells.
    • When cells get damaged due to trauma they need to be replaced.
why cells reproduce growth development
Why Cells Reproduce…Growth & Development
  • Aging is inevitable.
  • But a cell only last so long.
    • Some last days, some decades
  • As one cell dies others replace it.
why cells reproduce replacing old cells
Why Cells Reproduce…Replacing Old Cells
  • What constitutes an old cell?
  • A cell is old when it gets too big.
  • As a cell ages it grows by producing more proteins & more organelle.
  • As a cell grows its surface-area-to-volume ratio decreases.
but why are cells small
But Why Are Cells Small?
  • Cells are small because large cells become inefficient at getting things in & out.
looking at cells
Looking at Cells
  • What does that mean?
  • Small cells function more efficiently than large cells.
  • It’s tied to the comparison between the surface area of the cell (the surface the cell uses to get things in and out) and the volume it performs life functions.
  • This is called the surface area-to-volume ratio.
think of a cell as a protein factory
Think of a Cell as a Protein Factory


Amino acids, sugars, lipids


surface area to volume ratio
Surface Area-To-Volume Ratio
  • Think of it like this:
  • For every unit of surface area, one thing can move in or out.
  • For every unit of volume, one protein or waste can be created.
  • When a cell gets too large, it quickly becomes too crowded with stuff on the inside and doesn’t have enough surface area to move the stuff out.
  • The factory gets backed up without enough doors!
relationship between surface area and volume
Relationship between Surface Area and Volume

Smallest cell gives the largest ratio!...  More doors!

Cell Surface Area to Volume Animation

why cells reproduce replacing broken cells
Why Cells Reproduce…Replacing Broken Cells
  • What constitutes BROKEN CELLS
  • Cells damaged from:
    • Trauma
    • Burns
    • Cancer
  • What are three reasons cells reproduce?
    • To allow an organism to grow.
    • To replace old cells (that get too big).
    • To allow an organism to replace damage.
  • What are the two limiting factors to cell size…therefore other reasons cells divide?
    • To maintain high surface area to volume ratios.
    • To maximize the usefulness of DNA.
why cells reproduce making new cells
Why Cells Reproduce, Making New Cells
  • This all ties in to one major theme.
  • Other than repairing broken cells or for growing…
  • Cells divide when they reach a certain size, because larger cells are more difficult to maintain.
  • Small cells are MUCH more efficient than large cells.
facts of cell division
Facts of Cell Division
  • When a cell divides it forms “daughter” cells
  • Each newborn “daughter” cell is smaller than the parent and has a higher surface area–to-volume ratio than its parent does.
  • Also, each new daughter cell gets an entire, exact copy of the parent cell’s DNA.
  • They are, in essence, identical twins & clones of the parent.
what must happen first dna packaging
What Must Happen First…DNA Packaging
  • You now know why a cell divides.
  • It’s to replace old or damaged cells,…
  • To grow,…
  • Or when the cell reaches a certain size.
  • Now, before you learn about the process of mitosis, you need to learn about the structure of chromosomes.


  • You know that DNA carries __________ __________.
  • The genetic information is arranged on large molecules of DNA organized into hereditary units called genes.
    • A gene is a unit of heredity that consists of a segment of nucleic acid that codes for a functional unit of RNA or protein.
  • Ultimately, genes in DNA are organized and packaged (condensed) into structures called chromosomes.
    • Depending on the organism, chromosomes arelinear structures (eukaryote) or a circular structure (prokaryote) that is made up of DNA and proteins.

Eukaryotic Chromosomes

  • During most of a cell’s life, its chromosomes exist like spaghetti noodles floating around.
  • In this form, the genetic information is easily accessed to make proteins.
  • But before a cell can divide, the DNA must be condensed, or wound up into a smaller, more organized unit…into chromosomes.
  • They must condense so that DNA doesn’t get messed up during division.
1 st level of organization
1st level of Organization.

Eukaryotic Chromosomes

  • The first level of packaging is done by a class of proteins called histones. A complex of eight histones come together to form a disc-shaped core.
    • A type eukaryotic protein found in the chromosome
  • The long DNA molecule is wound around a series of histone cores in a regular manner to make what is called a nucleosome.
    • A eukaryotic structural unit of chromatin of DNA wound around histones
  • Under an electron microscope, this level of packaging resembles beads on a string.
2 nd level of organization
2nd Level of Organization
  • The 2nd Level
  • The string of nucleosomes line up in a spiral to form a cord that is 30 nm in diameter.
3 rd level of organization
3rd Level of Organization

Eukaryotic Chromosomes

  • The 30-nm nucleosome cord forms visible chromosomes around protein scaffolding.
  • These looped domains then coil into the final, most highly condensed form of the chromosome.
  • Many dense loops of chromatin form the rod-shaped structures that can be seen in regular light microscopes.
    • After the several condensing steps, the chromatin is dense enough to be seen by the eye in one of our microscopes

Eukaryotic Chromosomes

  • Chromosomes are drawn as “X”s
  • It’s actually 2 identical chromosomes that have been replicated joined in the center.
  • Each of the two thick strands of a fully condensed, duplicated chromosome are called achromatid.
    • Each chromatid is made of a single, long molecule of DNA.
  • Each of the chromosomes is made up of a complex of DNA & proteins called chromatin.

Eukaryotic Chromosomes

  • Identical pairs of chromatids, called sister chromatids, are held together at a region called the centromere.
    • The region of the chromosome that holds the two sister chromatids together during mitosis
  • Why do the sister chromatids need to be exactly the same?
  • During cell division, the sister chromatids are separated at the centromere, and one ends up in each daughter cell.
a chromosome under electron microscopy
A Chromosome Under Electron Microscopy

1 Sister Chromatid

1 Sister Chromatid

1 Chromosome

a chromosome under electron microscopy1
A Chromosome Under Electron Microscopy


The place where 2 sister chromatids are joined

a chromosome under electron microscopy2
A Chromosome Under Electron Microscopy



This is the stuff that all DNA in chromosome form is made of.

preparing for cell division
Preparing for Cell Division
  • All new cells are produced by the division of preexisting cells.
    • Where is this idea from?
    • Cell theory
  • The process of cell division involves more than cutting a cell into two pieces. Each new cell must have all of the equipment (organelle… mitochondria, etc) needed to stay alive.
  • All newly-formed cells require DNA too, so before a cell divides, a copy of DNA is made for each daughter cell...Replication
  • Each new daughter cell gets the exact copy as the other.
  • Each new cell will function in the same way as the cells that they replace.
preparing for cell division1
Preparing for Cell Division


  • The process of Prokaryotic cell division is called binary fission.
  • It happens in three steps.
  • The cytoplasm is divided when a new cell membrane forms between the two DNA copies.
  • The cell grows until it nearly doubles in size.
  • The cell is then constricted in the middle, like a long balloon being squeezed near the center.
  • Eventually the dividing prokaryote is pinched into two independent daughter cells, each of which has its own circular DNA molecule exactly the same as the parent.
prokaryotic chromosomes
Prokaryotic Chromosomes

Prokaryotic Chromosome Organization

  • Prokaryotes are much simpler than eukaryotes.
  • A prokaryotic cell has a single circular molecule of DNA.
    • Normally, it’s connected on both ends, in a loop
  • This loop of DNA contains thousands of genes.
  • A prokaryotic chromosome is condensed through repeated twisting or winding, like a rubber band twisted upon itself many times.
  • This is called supercoiling.
  • Tissue Regeneration
  • Pinky Nail Regrowth
summary answer these questions
Summary: Answer these questions.
  • Why do Cells Divide?
  • What happens to DNA before a cell can divide?
  • What helps DNA condense?
  • What is special about daughter cell and parent cell DNA?
  • Because larger cells are more difficult to maintain, cells divide when they grow to a certain size.
  • Many proteins help package eukaryotic DNA into highly condensed chromosome structures.
  • All newly-formed cells require DNA, so before a cell divides, a copy of its DNA is made for each daughter cell.
graphic assignment condensation and organization of dna label this structure in your notes
Graphic Assignment:Condensation and Organization of DNALabel this structure in your notes
graphic assignment condensation and organization of dna label this structure in your notes1
Graphic Assignment:Condensation and Organization of DNALabel this structure in your notes
preparing for cell division continued
Preparing for Cell Division, continued


  • Once supercoiled, the bacterial DNA is protected
  • In order for bacteria to divide the DNA must unwind, get copied and attached to the inner cell membrane
  • Once attached the bacteria is ready to divide.
preparing for cell division continued1
Preparing for Cell Division, continued


  • The reproduction eukaryotic cells is more complex than that of prokaryotic cells.
  • Reasons:
  • Eukaryotic cells have many organelles. In order to form two living cells, each daughter cell must contain enough of each organelle to carry out its functions.
  • The daughter cells being smaller only need a few organelle at first but as it grows, makes more of each organelle.
  • The DNA within the nucleus must also be copied, sorted, and separated.
  • Eventually, the daughter cells become mature cells, exactly like their parent cells, equipped with the same amount of DNA & organelle.
comparing cell division in prokaryotes and eukaryotes
Comparing Cell Division in Prokaryotes and Eukaryotes

Because of its complexity, eukaryotic cell division takes roughly 24 hours.

Prokaryotic cell division requires only 20 minutes. Being infected by one cell can result in our bodies being overrun by millions of bacteria in less than a day.

the organization of dna
The Organization of DNA
  • Take a piece of string and stretch it out.
  • This is how long all the DNA in just one cell would be if it were stretched out… 2 meters.
  • It takes great organization to get this much DNA to fit into each of the 100 trillion cells you have.
  • Try fitting two “chromosomes” into your “nucleus”.
  • Try once just shoving it in then wrap the chromosome around a paperclip.
  • Which way is more organized?
  • This organization is called condensation.
  • What does the word condensed mean?