Structure Leads to Function;The Cell Membrane

The Words…• STRUCTURE: the shape, organization,

and/or chemical makeup of an object• FUNCTION: what something does, its role• STRUCTURE always leads to FUNCTION!

Familiar Examples…• Eating Utensils: Fork, Spoon, & Knife

– These have distinct shapes that determine their use

A few microscopic examples…

• Microtubules

A few microscopic examples…

• Proteins… in all their variety

Take Home Message?

STRUCTURE LEADS

TO FUNCTION!!!!!

The Plasma (cell) Membrane• Structure: Made up of a lipid bilayer, proteins, &

cholesterol

Plasma Membrane

• Functions:– Forms the principle barrier between the inside of

the cell and its environment– Protect the cell– Regulate traffic into and out of the cell– Support the creation of multiple concentration

gradients and an electrostatic gradient between the inside and outside of the cell

– Maintain the overall integrity of the cell, particularly in cold temperatures

Structure of a Phospholipid

Chemical Structure• The chemical makeup of a phospholipid causes

multiple phospholipids to naturally align themselves in a characteristic bilayer shape (structure).– This is due to the chemical properties of the

phospholipid: the polar, hydrophilic head and the hydrophobic tail

• Function: hydrophilic region allows the plasma membrane to associate with water, other polar molecules, & hydrophilic proteins on the inside and outside of the cell

• Function: hydrophobic region creates a hydrophobic barrier to keep out large and/or polar/hydrophilic molecules

The Polar Head

• Structure: The “head” has a positively charged nitrogen atom and a negatively charged oxygen

• Function: The polarity of the head allows the membrane to associate easily with other polar molecules, such as H2O

Cholesterol Functions

• Function 1: Easily inserts into the plasma membrane between the tails of different phospholipids, thus filling in the gaps between phospholipids and helping to keep out other small molecules

• Function 2: Pay attention… it stiffens the membrane at “normal” temperatures, but keeps the membrane fluid at cold temperatures

Membrane Proteins

• Have both hydrophilic and hydrophobic regions, allowing them to associate with the plasma membrane in a variety of ways

• Come in all different shapes and thus, perform many different functions

• Specifically, help regulate traffic across the plasma membrane

Types of Transport

• There are 2 main categories of transport:– Passive– Active

PASSIVE TRANSPORT

• Does NOT require Energy• Gradient = “change in the value of a quantity

(as temperature, pressure,or concentration) with change in a given variable and especially per unit on a linear scale”

Facilitated Diffusion

• A form of Passive Transport… • Facilitated: to help or allow• Channel proteins, • Along their concentration gradient

Active Transport

• Necessary when transporting a particle against (up) its concentration gradient

• REQUIRES ENERGY– ATP

5 levels of organization

• 1.) Protoplasmic organization – Unicellular organisms: protozoa

• 2.) Cellular Organization – Sponges – Cells that are functionally differentiated and exhibit

a division of labor

• 3.) Tissue Level– Cells organized into layers which form tissue

• 4.) Organs – Composed of one or more tissues.– Have more specialized funtion than tissue– Flatworms: reproductive organs, eyespots, feeding

structures

• 5.) System level – Organs work together to form systems: circulatory,

digestive, reproductive, respiratory

Types of tissue

• Tissue: a group of similar cells specialized for the performance of a common function

Epithelial tissue

• Epithelial– Absorb: lining of small

intestine – Transport: kidney tubules– Excrete: sweat glands– Protect: skin– Contain nerve cells for

sensory info• Tastebuds

• The structure relates to their function.

Connective tissue

• Connective – Support and bind – Distributed throughout an

extracellular matrix – Loose connective tissue

• Elastic • Binds skin to muscle

– Fibrous connective tissue • Tendons (muscle to bone

or other muscle)• Ligaments (bones to

bones) – Adipose tissue:

• Store lipids • Form fat

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Muscle tissue • Muscle Tissue

– Allows movement • Skeletal• Smooth• Cardiac QuickTime™ and a

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Nervous Tissue

• Nervous Tissue – Impulse-conducting

cells• Neurons

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Organs

• Functional units of the body that are made up of more than one tissue – Heart– Lungs– Liver – Spleen – kidney

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Organ Systems

• Group of organs that complete a function – Work together

• Integumentary• Skeletal• Muscular• Nervous• Endocrine• Circulatory• Respiratory• Digestive• Reproductive

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