06 cell growth and reproduction

• CELL SIZE LIMITATION (8 .2)•THE CELL CYCLE (8 .2)

• CONTROL OF THE CELL CYCLE (8 .3)

Cell Growth and Reproduction

• WH Y C AN’ T OR GANI SMS BE JUST ONE GI ANT C E L L?

• I F A C E L L WANT S T O MAKE A C OPY OF I T SE L F, WH AT DO YOU T H I NK I S T H E F I R ST ST E P?

• WH AT OR GANE L L E S AR E I NVOLVE D I N C E LLUL AR R E PR ODUC T I ON?

Answer these questions:

Cell Size Limitation

Cell size is limited by… Diffusion rate DNA Surface area-to-volume ratio

Diffusion Rate Fast and efficient over short distances Becomes slow and inefficient as distances become

larger

Cell Size Limitation

DNA To build proteins, the blueprints for those proteins

(DNA) must be copied The cell cannot survive unless there is enough DNA to

support the protein needs of the cell

Answer these questions: What does DNA code for? Where is DNA stored? How can we increase cell size and still have enough

DNA to support the protein needs of the cell?

Surface area-to-volume ratio As size increases, volume increases much faster than

surface area

Answer this question: How does the surface area-to-volume ratio affect cell

function?

Cell Size Limitation

Cell Size Limitation

Surface area-to-volume ratio The demand for oxygen, nutrients and waste removal

grows faster than the surface area of the plasma membrane allows

• WHAT 3 FACTORS LIMIT CELL SIZE?

• WHY DO WE (AND OTHER ORGANISMS) MAKE NEW CELLS?

• WHAT ARE CHROMOSOMES?

Answer these questions:

Cell Reproduction

Cell division results in two cells that are identical to the original, parent cell

Cells are constantly growing, dividing and dying

New cells are used for growth, repair/replacement

Cell Reproduction

In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes.

Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing.

However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope.

Cell Reproduction

For most of a cell’s lifetime, chromosomes exist as chromatin

Chromatin is long strands of DNA wrapped around proteins called histones

Cell Reproduction

Before a cell can divide, it must pack up and untangle the chromatin so it can be moved easily

We see chromosomes when the chromatin is tightly packed

https://www.youtube.com/watch?v=gbSIBhFwQ4s

The Cell Cycle

The cell cycle is the sequence of growth and division of a cell

The growth period is called interphase

The division period is called mitosis

The Cell Cycle - Interphase

Divided into 3 parts G1 – cell growth, high

protein production S – DNA synthesis G2 – Organelles and

other cell parts for cell division are assembled

The Cell Cycle - Mitosis

The 4 phases of mitosis Prophase Metaphase Anaphase Telophase

The Cell Cycle – Mitosis: Prophase

Prophase

The long stringy chromatin coils up into visible chromosomes

Each duplicated chromosome is made up of two halves called sister chromatids held together by a centromere

The Cell Cycle – Mitosis: Prophase

As prophase continues, the nuclear membrane and nucleolus disintegrate

In animals, two pairs of centrioles begin to migrate to opposite ends of the cell

The spindle (made of microtubules) begins to form

The Cell Cycle – Mitosis: Metaphase

Metaphase

The chromosomes line up across the middle of the cell

Each sister chromatid is attached to its own spindle fiber at the centromere.

The other end of the spindle fiber attaches to the centriole (in animals) or the cell wall (in plants)

The Cell Cycle – Mitosis: Anaphase

Anaphase

Anaphase is marked by the separation of sister chromatids

Centromeres split apart and each chromatid of a pair is pulled to opposite ends of the cell

The Cell Cycle – Mitosis: Telophase

Telophase

Chromatids reach the opposite poles of the cellChromosomes unwind The spindle breaks downThe nucleolus reappearsA new nuclear membrane forms around each

set of chromosomesA new plasma membrane begins to form

between the two new nuclei

Cytokinesis

Following telophase, the cells cytoplasm divides in a process called cytokinesis

In animal cells, the plasma membrane folds in at the equator

In plant cells, a cell plate is constructed between the two new cells, allowing new cell membranes and cell walls to form

Results of Mitosis

Mitosis results in 2 new cells with identical chromosome sets

The two daughter cells will carry out the same cellular processes and functions as those of the parent cell

Each daughter cell will grow and divide

Videos

Computer animated mitosis: https://www.youtube.com/watch?v=VGV3fv-uZYI

Black and White: https://www.youtube.com/watch?v=ZeW8HaCUtOQ

Colored: https://www.youtube.com/watch?v=P7m3WfzgZdI

Hank Green: https://www.youtube.com/watch?v=L0k-enzoeOM

Control of the Cell Cycle

Control of the Cell Cycle

At each checkpoint, if conditions are met, cyclin tells cyclin-dependant kinase to move to the next step of the cell cycle

Control of the Cell Cycle

DNA holds the code for the construction of cyclin, cyclin-dependant kinase and all of the other proteins and enzymes involved in control of the cell cycle

If the genes that code for any of these are mutated, dysregulation of the cell cycle occurs Checkpoints may not work The signal for cell division may be given when more

cells are not needed This is cancer