CELLSCell Structure and Function

Intro to Cells

• A cell is the smallest unit that can carry on all the processes of life

• The development of the microscope enabled scientists to take their first close look at cells

Discovery of the Cell• 1665 – Robert Hooke

– Examined cork (plant tissue) using a microscope

– The “little boxes” he observed under the microscope reminded him of the small rooms where monks live, so he named them cells

Robert Hooke

Discovery of the Cell

• 1673 – Anton van Leeuwenhoek– First person to observe living cells under

a microscope

Anton van Leeuwenhoek

I. The Cell Theory - summary of before mentioned scientists and other biologists is one of fundamental concepts of biology.

1. All living things are composed of cells.

3. New cells are produced from existing cells.

2. Cells are the basic units of structure and function in all living things.

II. Cells

a. Smallest- 0.2 micrometers (bacteria)

A. Cells come in many shapes and sizes.

b. Largest- birds egg and giant amoeba (1000 micrometers).

B. Prokaryotes and Eukaryotes- Scientists divide cells Into two groups depending on whether they have a nucleus or not.

1. Prokaryotes (Bacteria) - no nucleus!

a. Smaller and simpler than cells of eukaryotes.

b. Do have cytoplasm and cell membrane.

c. Still carry out all activities associated with life.

2. Eukaryotes - do contain nucleus and membrane bound organelles (includes plants, animals, fungi).

a. Contain cytoplasm and plasma (cell) membrane.

b. Also contain dozens of other specialized structures called organelles (means tiny organs).

C. Multicellular Organization

1. Cells are specialized to perform one or a few functions in multicellular organisms.

2. The levels of organization include:

Cells --> Tissues --> Organs --> Systems --> Organism

D. Cell structure as it relates to the function

1. Cells come in a variety of shapes, and the shape helps determine the function of the cell. – Nerve cells are long to transmit messages in the

body. – Red blood cells are disk shaped to move through

blood vessels.

E. Cell structure as it relates to the function

1. Animal cells can signal to one another in various ways. – (A) Hormones produced in

endocrine glands are secreted into the bloodstream and are sent throughout the body.

– (C) Nerve signals are transmitted along axons to remote target cells.

F. Receptor Proteins

1. An animal cell depends on multiple extracellular signals. Every cell type has receptor proteins that respond to specific signal molecules produced by other cells. 2. These signal molecules work in combinations to regulate the behavior of the cell. For example, cells may require multiple signals (blue arrows) to survive, (red arrows) to divide or not, and (green arrows) to differentiate. 3. If deprived of survival signals, most cells undergo a form of cell suicide known as programmed cell death.

III. Cell Structure

A. Plasma Membrane (cell membrane) – thin, flexible barrier around the cell.

1. Regulates what enters and exits the cell. Important in maintaining homeostasis.

2. Support and protect cells, while allowing them to interact with surroundings.

Lipid molecules

3. Made of double-layered sheet called- lipid bilayer.

4. Membrane is a “mosaic” of many different kinds of molecules (protein channels and pumps, carbohydrate that help cells recognize each other.

B. Cell Wall - found in plants, algae, fungi, nearly all prokaryotes. NOT animal cells

1. Lies outside the cell membrane- provides support and protection for the cell

2. It’s a strong layer made from fibers of carbohydrates (like cellulose) and proteins

C. Cytoplasm – The “juice” inside the plasma membrane, but not including nucleus. Also contains many important organelles.

D. Nucleus - large structure containing cell’s genetic material- controls cell’s activities (“brain”)

1. Controls most of cell processes and contains hereditary information (DNA) (controls activities by making proteins)

2. Found in eukaryotic cells

b. Chromosomes - chromatin condenses when cell gets ready to divide. Contains genetic material passed from one generation to the next.

3. Chromatin and Chromosomes - granular material visible inside the nucleus.

a. Chromatin - DNA bound to protein.

c. Nucleolus - small dense region in nucleus where ribosomes are made.

d. Nuclear envelope - double membrane layer surrounding the nucleus containing tiny nuclear pores (allows materials to move into and out of nucleus. i.e. RNA).

1. Network of protein filaments that help the cell to maintain its shape and involved in many forms of cell movement

2. Made up of microtubules and microfilaments

E. Cytoskeleton -

a. Microtubules- serve as “tracks” along which organelles are moved. Important in cell division- help to separate chromosomes. Also form cilia and flagella which allow cells to move

b. Microfilaments - long, thin fibers function in movement and support the cell

F. Organelles in the Cytoplasm- (act like specialized “organs” in the cell)

1. Ribosomes - makes proteins.

2. Endoplasmic Reticulum - cell’s internal transport system.

a. Connects nucleus to the cell membrane and acts as a transportation network in the cell.

b. Rough ER - (has ribosomes attached – makes proteins) and Smooth ER (no ribosomes) breaks down toxins and organics.

3. Golgi Apparatus - “post office” of the cell

a. Carbohydrates and lipids attached to proteins are “packaged”.

b. Then sent to final destination.

Golgi Apparatus

4. Lysosomes - “clean-up” crew of the cell.

a. Break down lipids, carbohydrates, proteins from food particles (little “digestive sacs”).

b. Break down ‘old’ cell parts, removing debris.

Lysosomes

5. Vacuoles - storage “sacs”- store water, salts, proteins, carbohydrates

a. Large in plant cells (single large vacuole)

b. In animals, smaller vacuoles called vesicles. They transport substances within the cell

6. Chloroplasts - found in plants and some other organisms (none found in animals and fungi).

a. Produce energy-rich food molecules from sunlight by photosynthesis.

b. Green pigment- chlorophyll found in photosynthetic membranes.

7. Mitochondria - found in nearly all eukaryotic cells.

a. Use energy from food to power growth, development and movement.

b. Cells that require more energy- have more mitochondria.

D. Mitochondrial DNA - DNA is also found in the mitochondria. Essential for normal function of both organelles.

1. This DNA is inherited from the mother only.

CELL Movement

I. Homeostasis – Keeping it balancedA. Homeostasis – Every living organism regulates its

internal environment to maintain a stable condition. Homeostasis exists at the cellular and the organism level.

1. Cellular examples: Cells maintain a stable internal acidity (pH), blood sugar (glucose) levels keep balanced, and water concentrations keep balanced.

2. Organism examples: Warm-blooded animals maintain a constant internal body temperature.

Click on link to see how blood glucose is regulated.http://www.bbc.co.uk/schools/gcsebitesize/biology/humansasorganisms/6homeostasisrev4.shtml

The next section will show how water and other molecule levels are regulated inside the cell.

II. Movement Through the Membrane

A. Cell Membrane - regulates what enters and exits the cell and provides support and protection

1. Lipid Bilayer- Double layered sheet (not soluble in water)

a. Contains protein molecules that form chemical “pumps” and channels to move material across membrane

b. Carbohydrate molecules act like “ID cards” allowing cells to identify each other

B. Diffusion- Movement of materials from areas of high concentration to areas of low concentration1. All living cells have a liquid interior

(cytoplasm) and are surrounded by liquid.2. Diffusion causes many

substances to move across cell membrane but does not require the cell to use energy (called passive transport).

3. Equilibrium- when the concentration of molecules are equal on both sides of membrane.

Why is it important not to put saltwater animals into freshwater

and freshwater animals into saltwater?

C. Osmosis- Diffusion of water molecules through selectively permeable membrane

1. Most membranes are selectively permeable (some materials can pass across membrane and others cannot) like “sieve”

2. Effects of osmosis on cell (i.e. Red blood)

a. Isotonic- “same strength”

These all refer to concentration of solute molecules

Isotonic solution

Water moves in and out of cell at the same speed. Cell stays the normal shape.

Isotonic solution

hypotonic solution

b. Hypotonic- “below strength”More dissolved particles inside the cell, so there is more water outside than inside. Water enters a cell by osmosis, causing the cell to swell and burst.

Isotonic solution

hypotonic solution

hypertonic solution

c. Hypertonic- “above strength”

Concentration of dissolved molecules is higher outside of cell, so lower water concentration outside. Water flows out of cell. Causes the cell to shrink.

Why are snails afraid of salt?

3. Osmotic Pressure- osmosis exerts pressure on hypertonic side of selectively permeable membranea. Cells filled with salts, sugars, proteins and

other molecules- always hypertonic to fresh water

b. Osmotic pressure produces movement of water into cell that is surrounded by fresh water.

c. Fortunately cells don’t come into contact with fresh water. Usually bathed in isotonic solutions (e.g. blood) or protected by cell wall (e.g. bacteria) or mechanism to pump out excess water (contractile vacuole)

D. Facilitated Diffusion- membrane proteins help (faciliate) the movement of certain molecules across the cell membrane by diffusion (from high conc. To low conc.) that can’t diffuse through lipid bilayer directly.

1. Many different protein channels for ions, sugars, salts.

2. Does not require addition of energy (passive transport)

Facilitated Diffusion

E. Active Transport- movement of molecules and ions against a concentration difference (from low to high)

1. Requires input of energy

2. Small molecules “pumped” across membrane (e.g. Na+ and K+ ions)

3. Large amounts of material transported through movements of the cell membrane

Sodium-Potassium Pump

Endocytosis vs. Exocytosis

• Endocytosis and exocytosis are active transport mechanisms in which large substances cross the membrane inside vesicles

Endocytosis

• In endocytosis, the cell membrane folds around something in the external environment and forms a pouch

• The pouch then pinches off and becomes a vesicle in the cytoplasm

• Endocytosis includes pinocytosis, in which the vesicle contains solutes or fluids, and phagocytosis, in which the vesicle contains large particles or cells

Endocytosis

Exocytosis

• In exocytosis, vesicles made by the cell fuse with the cell membrane, releasing their contents into the external environment

Exocytosis

UNIT III- CELLS

Cell Structure and Function

Which cell structure contains the cell's genetic material and controls the cell's activities?

a. organelle

b. nucleus

c. cell envelope

d. cytoplasm

Which cell structure contains the cell's genetic material and controls the cell's activities?

a. organelle

b. nucleus

c. cell envelope

d. cytoplasm

Prokaryotes lack

a. cytoplasm.

b. a cell membrane.

c. a nucleus.

d. genetic material.

Prokaryotes lack

a. cytoplasm.

b. a cell membrane.

c. a nucleus.

d. genetic material.

Eukaryotes usually contain

a. a nucleus.

b. specialized organelles.

c. genetic material.

d. all of the above.

Eukaryotes usually contain

a. a nucleus.

b. specialized organelles.

c. genetic material.

d. all of the above.

The main function of the cell wall is to

a. support and protect the cell.

b. store DNA.

c. direct the activities of the cell.

d. help the cell move.

The main function of the cell wall is to

a. support and protect the cell

b. store DNA.

c. direct the activities of the cell.

d. help the cell move.

Which organelle makes proteins using coded instructions that come from the nucleus?

a. Golgi apparatus

b. mitochondrion

c. vacuole

d. ribosome

Which organelle makes proteins using coded instructions that come from the nucleus?

a. Golgi apparatus

b. mitochondrion

c. vacuole

d. ribosome

Which organelle converts food into energy that the cell uses for growth, development, and movement?

a. chloroplast

b. Golgi apparatus

c. endoplasmic reticulum

d. mitochondrion

Which organelle converts food into energy that the cell uses for growth, development, and movement?

a. chloroplast

b. Golgi apparatus

c. endoplasmic reticulum

d. mitochondrion

The cell membrane contains channels and pumps that help move materials from one side to the other. What are these channels and pumps made of?

a. carbohydrates

b. lipids

c. bilipids

d. proteins

The cell membrane contains channels and pumps that help move materials from one side to the other. What are these channels and pumps made of?

a. carbohydrates

b. lipids

c. bilipids

d. proteins

Diffusion is the movement of molecules from

a. an area of low concentration to an area of high concentration.

b. an area of high concentration to an area of low concentration.

c. an area of equilibrium to an area of high concentration.

d. all of the above

Diffusion is the movement of molecules from

a. an area of low concentration to an area of high concentration.

b. an area of high concentration to an area of low concentration.

c. an area of equilibrium to an area of high concentration.

d. all of the above

Which means of particle transport requires input of energy from the cell?

a. diffusion

b. osmosis

c. facilitated diffusion

d. active transport

Which means of particle transport requires input of energy from the cell?

a. diffusion

b. osmosis

c. facilitated diffusion

d. active transport

The diffusion of water across a selectively permeable membrane is called

a. osmotic pressure.

b. osmosis.

c. facilitated diffusion.

d. active transport.

The diffusion of water across a selectively permeable membrane is called

a. osmotic pressure.

b. osmosis.

c. facilitated diffusion.

d. active transport.

An animal cell that is surrounded by fresh water will burst because the osmotic pressure causes

a. water to move into the cell.

b. water to move out of the cell.

c. solutes to move into the cell.

d. solutes to move out of the cell.

An animal cell that is surrounded by fresh water will burst because the osmotic pressure causes

a. water to move into the cell.

b. water to move out of the cell.

c. solutes to move into the cell.

d. solutes to move out of the cell.

Which term refers to cells having different jobs in an organism?

a. multicellular

b. cell specialization

c. levels of organization

d. unicellular

Which term refers to cells having different jobs in an organism?

a. multicellular

b. cell specialization

c. levels of organization

d. unicellular

What is the name of structure (a.)?

Rough Endoplasmic reticulum

What is the name of structure (b.)?

ribosome

Is this cell an animal or plant cell?

Animal cell

What is the name of structure (c.)?

Cell membrane

What is the name of structure (k.)?

nucleolus

What is the name of structure (g.)?

Golgi bodies

What is the name of structure (e.)?

Smooth endoplasmic reticulum

What is the name of structure (d.)?

mitochondria

What is the name of structure (m.)?

vacuole

What is the name of structure (k.)?

Cell membrane

What is the name of structure (j.)?

Cell wall

What is the name of structure (l.)?

chloroplast

What is the name of structure (f.)?

nucleus

What cell structures found in the organism below is responsible for removing excess water from the inside of the cell?Contractile vacuole

What cell process is taking place below?

osmosis