When you see a newborn baby, is it hard for you to imagine that just nine months ago, that baby was a single cell? Something to think about... When you see a towering oak tree, can you believe that it was once a measly acorn? When you mow the lawn on Saturday, can you believe that by next Saturday, you have to do it again? Can you believe that every second, your body makes 25 million new cells?
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When you see a newborn baby, is it hard for you to imagine that just nine months ago, that baby was a single cell? Something to think about... When you.
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When you see a newborn baby, is it hard for you to imagine that just nine months ago, that baby was a single cell?
Something to think about...
When you see a towering oak tree, can you believe that it was once a measly acorn?
When you mow the lawn on Saturday, can you believe that by next Saturday, you have to do it again?Can you believe that every second, your body makes 25 million new cells?
Cell Growth and Reproduction
What Limits Cell Size?
Why can’t organisms be just one giant cell?
1 Diffusion
2 DNA Content
3 Surface Area to Volume Ratio
Diffusion
= Mitochondrion
Oxygen
Glucose
Waste
Waste
Cells can metabolize only as quickly as they receive raw materials. An average-sized cell with a diameter of 20um will receive supplies in a fraction of a second.
So long, big cell!
What if the cell were 20cm in diameter?
DNA Content
Most cells contain only one nucleus responsible for programming all
metabolism.DNA
RN
A
If the ribosomes don’t receive enzyme and protein-making instructions from the RNA, guess what?So long, big cell!
Surface Area-to-Volume Ratio
As a cell’s size increases, its volume increases much faster than its surface area.
3 cm
1 cm
2 cm
Volume l x w x h
Surface Area l x w x #
sides1 cm3
8 cm3
27 cm3
6 cm2
54 cm2
24 cm2
27 X 9 X
You Know!So long, big cell!
So, what must the cell do?
DIVIDE
Functions of Cell Division
In multicellular eukaryotes:– Growth and development– Replace old, worn-out and dying cells and
tissues– Sexual reproduction – making of gametes,
or sex cells (sperm and egg)
In unicellular prokaryotes:–Asexual reproduction
Types of Reproduction
Asexual Reproduction– Formation of offspring from one parent– Offspring are genetically identical to the parent– Leads to lack of genetic diversity among offspring
~ disadvantage in changing environment– Types include:
Division of a prokaryotic cell into two offspring cells
Types of Reproduction
Sexual Reproduction– Formation of offspring by uniting gametes
from two parents– Offspring are genetically different from the
parents– Increases variation in the population by
making possible genetic recombination
Eukaryotic Cell Reproduction
Before cell division, DNA coils tightly around histones (proteins) and forms chromosomes
Chromosomes (rod-shaped structures made of DNA and protein) must be duplicated in order for each daughter cell to receive identical copies of the parental chromosomes; each chromosome consists of two identical halves called sister chromatids held together by a centromere
Chromosome Structure
Sex Chromosomes and Autosomes
Humans’ somatic, or body cells, have 23 pairs of chromosomes (46 = diploid or 2n number) – first 22 pair are autosomes; last pair are sex chromosomes
XX=female
XY=male
The two copies of each autosome are called homologous chromosomes, or homologues (same size and shape and carry genes for same traits
Chromosome numbers of various species
Cell Cycle – Cell Division in Eukaryotes
G1 -- Period of cell growth before DNA is duplicated
S -- period when DNA is duplicated
G2 -- period after DNA is duplicated; cell prepares for division; end of interphase
Telophase
Anaphase
Metaphase
Prophase
G1, S, and G2 = InterphaseProphase, Metaphase, Anaphase, Telophase =
MitosisI Passed My Algebra Test
Mitosis Overviewwww.biologycorner.com/images.html
Interphase – G1, S, G2
The cell is engaged in metabolic activity and performing its preparation for mitosis.
Chromosomes are not clearly visible in nucleus, but the nucleolus may
be visible. Centrioles (or microtubule organizing centers) may be visible during this
phase.
nuclear membrane
nucleus
chromatin
Interphase – G1, S, G2 In G1 or first growth phase, cells mature and increase
in size by making more cytoplasm and organelles
S or Synthesis phase follows G1 and results in the replication of genetic material Cell makes all structures needed to divide in G2 or second growth phase
nuclear membrane
nucleus
chromatin
Prophase
Chromatin in the nucleus begins to condense and becomes visible in light microscope as
chromosomes.
Nucleolus disappears. Centrioles in animal cells begin moving
to opposite ends of the cell and fibers extend from the centromeres.
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Prophase
Metaphase
Spindle fibers align the chromosomes along the middle of the cell nucleus, or equatorial plate.– This organization ensures that in the next phase,
each new nucleus will receive one copy of each chromosome.
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Metaphase
Anaphase
The paired chromosomes separate at the centromere and move to opposite sides of the cell; after chromatids separate, they are considered to be individual chromosomes.
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Anaphase
Telophase
Chromatids arrive at opposite poles ofthe cell and new membranes form around the daughter nuclei.
Chromosomes uncoil and are no longer visible under the light microscope.
Cytokinesis begins. Cell Plate or Cleavage Furrow
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Telophase
Cytokinesis
In animal cells, cytokinesis results when a cleavage furrow forms and
pinches the cell in two.
In plant cells, cytokinesis occurs when vesicles from the Golgi apparatus fuse to form a cell plate.
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Cytokinesis
Animal Cell - Mitosis
Plant Cell - Mitosis
Mitosis Video Review
•Video Link #1 - Youtube
•Video Link #2 – Cells Alive
•Video Link #3 – DNAtube
Cell Reproduction Following the completion of the cell cycle, two
daughter cells result, with the same number of chromosomes as the parent cells.
46
46
46
46
46
46
46 46
14
14
14 14
GORILLA GARDEN PEAHUMAN
So… What Are The Results?
Genetic continuity, i.e., two new cells with chromosome sets identical to the parent cell.
Daughter cells will carry out the same cellular processes and functions as their parent cell and will grow until the limitations of cell size force them to divide.
Control of Cell Division
Three checkpoints control division– Cell growth (G1) checkpoint: proteins control
whether the cell will divide– DNA synthesis (G2) checkpoint – DNA repair
enzymes check results of DNA replication;if checkpoint is passed, proteins will signal the cell to begin mitosis
– Mitosis checkpoint – if a cell passes, proteins signal the cell to exit mitosis and enter G1 again
When Control is Lost
If mutation occurs in one of the genes (p53 gene) that regulates cell growth and division, proteins may not function properly– This may lead to cancer, or the
uncontrolled growth of cells – Environmental influences may also play a
role, e.g., UV rays, radiation, X-rays– ONCOLOGY – study of cancer
To Review...
Limits of Cell Size– Diffusion– DNA Content– Surface Area-to-Volume Ratio