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Cells and The Cell Theory

IB Bio Topic 2

Cell Theory

1. Living organisms are composed of cells.

2. Cells are the smallest unit of life.

3. All cells come from pre-existing cells. (no spontaneous generation)

Evidence• When living things are observed under the microscope they consistently appear to be composed of cells.

• Cells carry out cell division to form new cells: Mitosis

Pg. 78: Cell Theory

• Viruses are not made up of cells.

• Where did the first cells come from?

• Mitochondria and chloroplasts contain their own DNA.

Humongous fungus among us- Armillaria bulbosa

is among the oldest and largest living things on Earth.

- Single fertilized spore.

- Vegetative growth using Hyphae

http://www.crystalfalls.org/humongou.htm

Exceptions

• Cell Theory Exceptions: – Muscle cells are multinucleated (have many nuclei)

– Fungi- are very large with many nuclei & a continuous cytoplasm.

• Viruses reproduce via host’s cell division (Mitosis.)

Pg. 78: Cell Theory

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Unicellular organisms carry out all the life functions

• Unicellular organisms evolved some 3-4 BYA• They were the dominant life form until 600 MYA• Life Functions:

1. metabolism2. response 3. homeostasis4. growth5. reproduction6. nutrition

Molecule Size• 1. Molecules (1nm).• 2. Cell membrane thickness (10nm).• 3. Virus (100nm).• 4. Bacteria (1µm).• 5. Organelles (less 10µm).• 6. Cells (<100 µm).• 7. Generally plant cells are larger than animal cells.

Pg. 87: Cell Sizes

Linear MagnificationLinear Magnification•• Magnification = measured length of the Magnification = measured length of the

image /measured length of the specimenimage /measured length of the specimen

Surface Area: Volume• As the size of a structure increases the surface area to

volume ratio decreases

• What does this all mean for the organism?

Rate of heat/waste production & resource consumption dependent on volume

Rate of material exchange dependent on surface area

Emergent Properties

• Arise from the interaction of component parts: the whole is greater than the sum

of its parts

With a partner, discuss what this

means. Give examples.

Differentiation & Specialization• Differentiation: Cells diverge within a multicellular organism as they specialize their function.

• Specialized cells have switched on particular genes that correlate to these functions.

• These specific gene expressions produce particular shapes, functions, & adaptations within a cell. (environment)

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Stem Cells• A stem cell has the capacity to divide and to differentiate along different pathways.

• These cells are able to divide but have not yet expressed genes to specialize yet.

• Under the right conditions stem cells can be induced to become a specific cell.

Pg 123: Stem Cells & Tissue Engineering.

http://www.dnalc.org/resources/animations/stemcells.html\

Stem Cell Use: Non-Hodgkins Lymphoma

1. Heavy does of radiation &/or chemotherapy to destroy diseased tissue (healthy blood tissue)2. Blood is filtered for the presence of peripheral stem cells (Cells that can still differentiate into different types of blood cells).

Stem Cell Use: Non-Hodgkins Lymphoma3. Bone marrow removed.

4. Healthy stem cells transplanted back to produce healthy blood cells again.

http://bcs.whfreeman.com/thelifewire/content/chp19/1902001.html

Non-Hodgkins vs. Hodgkins LymphomaLymphomas, a type of cancer that originates in wbcs called lymphocytes.

Abnormal cells are “Reed-Sternberg cells” = Hodgkin’s Lymphoma.

Reed-Sternberg cell is not present =

Non-Hodgkin’s.

Prokaryotic CellsProkaryotic Cells

Diagram of a prokaryote

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Is the region of the cytoplasm that

contains DNA. It is not surrounded by a nuclear membrane. DNA is always a closed loop (i.e. a

circular)

Nucleiod

used in protein synthesisRibosome

Contains all the enzymes needed

for all metabolic reactions, since there are no organelles

Plasma Membrane

Controls the entry and exit of substances; contains

peptidoglycan

Cell Wall

FunctionStructure long thread like attachments are generally considered to be for movement.

Flagella

Used for sticking cells together, as a food reserve, as protection against desiccation

and chemicals, and as protection against phagocytosis.

Slime Capsule

Thread-like projections are more numerous than the flagella. Associated with movement. Involved in the transfer of DNA in a process

called conjugation

Pili

Electron Micrograph

• Note the double membrane

• There is some evidence

in the image of pilli

• In the cytoplasm there are no visible organelles

which is consistent with how we expect a

prokaryote cell to appear

• The nucleoid region is not

seen in this image

Binary Fission

• Prokaryotic cells divide by binary fission

• asexual reproduction in which a cell divides into two same sized cells

• The cells are genetically identical and form the basis of a reproductive clone

Pg. 81: Bacterial Cells

Eukaryotic Cells

Draw and label a diagram of a liver cell

• N:Nucleus

• PM: plasma membrane

• M: mitochondria

• rER: Rough endoplasmic reticulum

• GA: Golgi apparatus

• L: Lysosome

• MV: Microvilli

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Nucleus

• Largest of the organelles.

• Contains the chromosomes which during interphase are to be found the nucleolus.

• Has a double membrane with pores.

Nucleus

• Controls cell functions through the expression of genes.

• Some cells are multi nucleated. What are some examples/types?

Plasma Membrane• Controls which substances can enter and exit a cell. (selective permeability)

• Fluid structure that can change shape. (fluid mosaic model)

• Double layer with pores (phospholipidbilayer)

Plasma Membrane• Receptors in the outer surface detect signals to the cell and relay these to the interior.

Mitochondria• Location of aerobic respiration and the synthesis of ATP.

• Double membrane organelle.

• Centre of the structure is called the matrix.

Mitochondria• Inner membrane has folds called cristae in which oxygen is consumed & the synthesis of ATP occurs.

• The more active a cell the greater the number of mitochondria.

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MitochondrionMitochondrionEndoplasmic Reticulum

• These are attached to the nucleus.

• Protein synthesis & packaging into transport vesicles.

Endoplasmic Reticulum• The 'rough' on the reticulum is caused by the

presence of ribosomes. (rER)

• Proteins made here are secreted out of the cell.

Free ribosomes produce proteins for internal use within the cell.

Golgi Apparatus• Center of synthesis, storage, sorting, &

transport.

• Modification of proteins from rER prior to

secretion.

Golgi Apparatus• Possible addition of carbohydrate or lipid

components to protein.

• Packaged into transport vesicles

for secretion.

Lysosomes• Form on the golgi apparatus.

• Contain hydrolytic enzymes. (digestion)

• Compartments that digests old organelles, engulfed bacteria, & viruses.

http://www.lahc.cc.ca.us/biology/bio3/mchernoff/quiz.html

Pg 88-90: Cell Structures & Organelles

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��Contain a cell wallContain a cell wall

��Have chloroplastsHave chloroplasts

��Large vacuolesLarge vacuoles

��Rectangular shapedRectangular shaped

Animals� Do notDo not contain a cell wallcontain a cell wall

��Do notDo not contain contain chloroplastschloroplasts

��Have small vacuolesHave small vacuoles

��Generally have spherical Generally have spherical shape.shape.

��Contain centriolesContain centrioles

��CiliaCilia

Membrane structure & proteins

• The fluid mosaic model of the plasma membrane.

Phospholipids

• Hydrophilic molecules are attracted to water.

• Hydrophobic molecules are not attracted to water but have an affinity for one another.

• Stability provided by hydrophobic tails in the center & hydrophilic heads & surrounding water.

Simple Diffusion

The movement of particles from an area of high [ ] to an area of low [ ] through the spaces in the

phospholipid bilayer.

Facilitated DiffusionThe diffusion of particles that are unable to pass through the spaces in the phospholipidbilayer.

Channel proteins control this movement of particles but not the direction of flow. Still H���� L

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Specificity of these proteins for each molecule.

Ex: Voltage-gated channels have channel proteins for Na & K in neuron membranes.

Osmosis• The plasma membranes are usually

freely permeable to water.

• Solvents are liquids in which particles dissolve.

• Solutes are the particles that dissolve.

• The diffusion of water is due to the concentration of solutes.

Osmosis• Therefore osmosis is the diffusion of water from an area of low solute [ ] to an area of high solute [ ] across the plasma membrane.

The attraction is between the H2O & the solute particles.

Types of SolutionsHypertonic: A hypertonic solution contains a greater [ ] of solutes than the inside of the membrane.

Tap water is hypertonic to distilled water.

Types of Solutions

Hypotonic: A hypotonic solution contains a smaller [ ] of solutes than the inside of the membrane.

Types of Solutions

Isotonic: Isotonic is the term used when there is an equal concentration of solutes.

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Active Transport Across Membranes

• Active transport involves transport using ATP (energy) by the cell.

• Active transport moves from low [ ] to

high [ ] against a concentration gradient.

Active Transport Across Membranes

Phagocytosis

Phagocytosis is a process in which a cell engulfs undissolved, large particles by flowing around them and enclosing them in a vacuole.There are 2 ways this can be done.

Endocytosis and Exocytosis

1. Endocytosis is when the surface membrane encloses materials and allows them inside.

2. Exocytosis is when the surface membrane encloses materials and allows them outside.

Pinocytosis “cell drinking”�The process in

which liquids or very small particles from the surrounding medium are taken into a cell.

Exocytosis Vs. Endocytosis

• Process of exporting molecules from a cell by fusion of vesicles with the cell membrane.

• Vesicle usually budded from the ER or Golgi.

• Used by secretorycells to export products.

• Process of importing molecules into a cell by forming vesicles derived from the plasma membrane.

• Used by cells to incorporate extracellular substances.

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Active Transport Across Membranes Active Transport Across Membranes

Topic 2.5 Cell division Cellular Division

•• Consists of two Consists of two

processes:processes:

1. Nuclear division1. Nuclear division

2. Cytoplasmic division2. Cytoplasmic division

Nuclear division

•• The process of nuclear The process of nuclear

division is called division is called mitosismitosis

•• The division of the entire cell The division of the entire cell

is called is called mitotic cell divisionmitotic cell division

Mitosis•• An orderly series of complex An orderly series of complex changes in the nucleus.changes in the nucleus.

•• Involves an exact duplicate of the Involves an exact duplicate of the complete set of chromosomes and complete set of chromosomes and the separation of these the separation of these chromosomes into chromosomes into two identical two identical sets.sets.

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The Cell Cyclein Eukaryotes

The Cell Cycle• The cell cycle describes the major phases of activity in the division of a cell.

• The length of the cell cycle depends on the particular function of the cell.

• Ex: bacterial cells can divide every 30 minutes.

• Skin cells divide about every 12 hours.

• Liver cells every 2 years.

• Muscle cells never divide at all after maturing.

• The total length of a cell cycle varies depending on the specialised function of a cell.

• Interphase is the longest phase which itself occurs in three stages.

• G1 The cell performs its normal differentiated function. Protein synthesis/ mitochondria replication/ chloroplast replication.

• S DNA replication. At this point the mass of DNA in the cell has doubled.

• G2 Preparation for cell division

The Cell Cycle• Phases of mitosis (PMAT) • Cytokinesis: division of the cytoplasm to form two daughter cells.

The Cell Cycle

Mitosis & Cancer

• Tumors are not foreign invaders.

• They arise from the same material used

by the body to construct its own tissues.

• Tumors use the same components -

human cells- to form the jumbled

masses that disrupt biological order and

function.

http://www.caletavip.net/videos/woman-has-a-300-pound-tumour-removed-from-her-stomach-x+h3uMp+yNmqvek.html

Interphase• An active period in the life of a cell when many metabolic reactions occur:

• Protein synthesis

• DNA replication

• Increase in the number of mitochondria &/or chloroplasts.

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Prophase• Supercoiling of chromosomes from

chromatin.

•• SingleSingle--stranded chromosomes replicate into stranded chromosomes replicate into

a a doubledouble--stranded chromosomes.stranded chromosomes.

•• CentrosomesCentrosomes migratemigrate to opposite ends or to opposite ends or

poles of the cell forming poles of the cell forming spindle fibers.spindle fibers.

• Attachment of spindle microtubules to

centromeres (kinetochore)

• Nucleus & nulcleolus disappear.

DoubleDouble--stranded chromosomestranded chromosome

•• Made up of two Made up of two

chromatidschromatids. .

•• Joined in the Joined in the

center by a center by a

centromerecentromere..

Metaphase•• The doubleThe double--stranded stranded

chromosomes line up in the chromosomes line up in the middlemiddle of the cell.of the cell.

•• This creates the This creates the metaphase metaphase plate.plate.

Anaphase•• The doubleThe double--stranded stranded

chromosomes break at the chromosomes break at the centromere and divide into singlecentromere and divide into single--stranded sister chromosomes.stranded sister chromosomes.

•• The sister chromosomes move to The sister chromosomes move to oppositeopposite poles with the aid of poles with the aid of shortening spindle fibers.shortening spindle fibers.

Telophase•• Last phase of mitosis.Last phase of mitosis.

•• Chromosomes reach the poles & uncoil.Chromosomes reach the poles & uncoil.

• Re-formation of nuclear membranes & &

nucleolus.nucleolus.

•• Results in 2 Results in 2 diploiddiploid daughter cells that are daughter cells that are

the exact replica of the parent cell. the exact replica of the parent cell.

(diploid)(diploid)

•• CytokinesisCytokinesis ((cytoplasmiccytoplasmic division) takes division) takes

place. place.

Cytokinesis•• Known as cytoplasmic division.Known as cytoplasmic division.

•• Here the cytoplasm of the cell is Here the cytoplasm of the cell is divided into two daughter cells, divided into two daughter cells, each containing one newly each containing one newly formed nuclei with an identical set formed nuclei with an identical set of chromosomes.of chromosomes.

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Mitosis in Plants

•• Plant cell division differs from animal cell division Plant cell division differs from animal cell division

in in twotwo ways:ways:

1. Most plants 1. Most plants do notdo not have Centrioleshave Centrioles

2. Plants have a rigid cell wall which prevents the 2. Plants have a rigid cell wall which prevents the

cell membrane from pinching in. cell membrane from pinching in.

Instead, a Instead, a cell platecell plate forms which divides the cell in forms which divides the cell in

half.half.