3- cell structure and function how do things move in...

3- Cell Structure and FunctionHow do things move in and

out of cells?A Quick Review

Taft College Human Physiology

How do things move in and out of cells?

• Things may move through cell membranes by Passive Processes

• Passive Processes do not require energy use by the cell and include:

• 1- Diffusion• 2- Osmosis• 3- Bulk Flow• 4- Facilitated Diffusion

How do things move in and out of cells?

• Things may move through cell membranes by Active Processes

• Active Processes do require energyexpenditure by the cell and include:

• 1- Active Transport• 2- Vesicular Transport

A. Endocytosis1. Pinocytosis2. Phagocytosis3. Receptor mediated endocytosis

B. Exocytosis

Active Processes• 1. Active transport• Active transport is the movement of

molecules across a cell membrane from an area of lower concentration of those molecules to an area of higher concentration of those molecules.

• It requires energy expenditure by the cellto move molecules from a [Low] to [High] against a concentration gradient.

•Passive Processes do not require energy use by the cell as they move molecules from a [High] to [Low] with the concentration gradient.•Active Transport requires energy expenditure by the cell to move molecules from a [Low] to [High] against a concentration gradient.

[High]

[Low]

Active Processes• Active transport• The concentration of molecules within a cell is

so important to the function of the cell that that the cell uses about 40% of it’s energy (ATP) for active transport to get the molecular concentrations just right.

• Active transport uses a lot of energy because molecules are constantly “leaking” through the cell membrane from [High] to [Low] due to what process?

• Diffusion – diffusion moves molecules in the opposite direction of active transport.

Active Processes• Active transport may include transport of molecules such as

Na+ and K+.

• The text will talk in terms of the sodium-potassium pumpor Na+/K+/ATPase pump when referring to active transport.

• Some drugs and poisons affect the active transport of molecules.

• Cyanide is lethal as it turns off ATP production and shuts down active transport in cells throughout the body.

• Digitalis slows the sodium pump causing sodium to accumulate in the cardiac muscle cell, causing a stronger heart beat.

• Digitalis strengthens heart contractions, slows heart rate, and helps eliminate fluid from body tissues. Digitalis is used to treat congestive heart failure, and certain arrhythmias. (Comes from foxglove plant).

Active Transport

The sodium-potassium pump (NA+/K+ ATPase) expels sodium ions (Na+) and brings potassium ions (K+) into the cell. ATP powers pump.

1. 3 Na+ inside cell bind to pump protein

2. ATP changes the shape of the pump and 3 Na+ are expelled

3. 2 K+ bind to the open end of the pump and trigger the release of the phosphate group which changes the shape of the pump.

4. Pump goes back to original shape and releases 2 K+ inside of cell.

Active Transport of Na+

Cell

HighNa+

Low

Na+

By

Diffusion

Na+ - K+Transport

Protein

LowNa+

High Na+

Na+

By Active Transport

Active Transport of K+

Cell

Low K+

High

K+

By

Diffusion

High K+

Low K+

By Active Transport

K+Na+ - K+ Transport

Protein

Active Transport of K+ and Na+

Cell

Na+ - K+Transport

Protein

LowNa+

High Na+

Na+ - K+ Transport

Protein

High K+

Low K+

Note! Ion concentration inside and outside the cell

is crucial to the function of the cell!

K+ is pumped in, Na+ is pumped out.

Active Processes

• Vesicular transport• A vesicle is a small, membrane bound sac.• Vesicles may be used to transport a variety of

substances into or out of the cell• In endocytosis, materials move into a cell in a

vesicle formed from the cell membrane.• In exocytosis, materials move out of the cell

when a vesicle formed in the cell fuses with the cell membrane.

Active Processes-Vesicular transport

• There are 3 types of endocytosis• 1. Phagocytosis = cell eating (solids)• 2. Pinocytosis = cell drinking (liquids)• 3. Receptor mediated endocytosis

Active Processes-Vesicular transport

• In Phagocytosis (cell eating), solid particles are engulfed by the cell membrane, become enclosed in a sac (vesicle) and moved into the cell.

• The solid material “ingested” may then be digested by digestive enzymes found in the lysosomes of the cell. See fig.

• Ex. – Phagocytic cells like neutrophils and macrophages feed on and destroy bacteria and other invaders of the body.

Endocytosis/Phagocytosis

Phagocytosis is a vital defense mechanism that helps protect the body from disease.

Endocytosis-Phagocytosis

Endocytosis-Phagocytosis

Active Processes-Vesicular transport

• In Pinocytosis (cell drinking), tiny droplets of extracellular fluid are surrounded by the cell membrane and taken into the cell.

• Pinocytosis is also called bulk-phase endocytosis. See fig.

Endocytosis - Pinocytosis

Most body cells carry out pinocytosis, to take in tiny droplets of fluid.

Active Processes-Vesicular transport

• In receptor-mediated endocytosis specific molecules or particles bind to specific receptor proteins on the cell membrane and trigger the cell to engulf extracellular material.

• 1. Cholesterol, iron, and vitamins can be transported this way.

• 2. Hormones (chemical messengers) can be picked up this way.

• *3.Viruses enter the cell this way. HIV virus enters by binding to a CD4 receptor.

• What happens if you do not have this receptor?• 1 in 10,000 people do not have the CD4 receptor , so

can not get AIDS!• Don’t engage in unsafe sexual practices hoping you or

your partner are the 1 in 10,000 that can not get aids.That’s poor odds!

Receptor Mediated Endocytosis

Receptor-mediated endocytosis imports materials needed by cells.

Active Processes/ Exocytosis

• Exocytosis serves to release materials from the cell.

• All cells carry out exocytosis.• Ex. 1.Cells that secrete digestive

enzymes, hormones, mucus, or other secretions

• 2. Nerve cells (neurons) that secrete neurotransmitters.

Cell Structure and Function

• The cell structures we see using microscopes in our lab are:

• 1. Nucleus = control center of the cell. The nucleus directs cell activity

• 2. Cytoplasm = “cell soup” between the cell membrane and the nucleus with many organelles we will discuss.

• 3. Cell or Plasma Membrane

Typical structures found body cells and seen with a lab microscope.

Cell Membrane Chemistry and Anatomy

• All membranes are composed of 2 major components.

• 1. Membranes contains a Lipid Portion.• 2. Membranes contain a Protein Portion.• Not all membranes are alike, they differ in the

proportion (ratio) of lipid and protein.• Membranes have been described as proteins

floating in a sea of lipids.• Let’s take a look at how the lipids and proteins

are arranged.

Cell membrane made of lipids and proteins

The Lipid Molecule

• A lipid (phospholipid) is diagrammed below

• The head is charged and hydrophyllic = water loving.

• The tail end has no charge and is hydro phobic = water fearing.

Hydrophyllic “water-loving” head = charged

Hydrophobic “water-fearing” tail = no charge

Arrangement of lipids in a membrane

• Lipids form a bi-lipid layer in the membrane with the hydrophyllic heads to the outside and inside of the membrane

where water is present. Materials not soluble in lipids will have to pass through the protein portion of the membrane

Phospholipid bilayer with embedded proteins

Functions of Proteins in Cell Membranes

• 1. protein channel for specific ions• 2. transport proteins for specific

substances• 3. receptors for hormones or other

substances• 4. enzyme (catalyst)• 5. cell identity markers = antigen (self

recognition)

Functions of Proteins in Cell Membranes

1. protein channel for specific ions

2. transport proteins for specific substances

3. receptors for hormones or other substances

4. enzyme (catalyst)

5. cell identity markers = antigen (self recognition)

Functions of Membranes

• 1. Limit boundaries of cell• 2. Control passage of substances

(selective) –see next slide• 3. Membranes are involved in enzyme

controlled reactions• 4. Membranes contain binding sites

(receptors) for certain chemicals

Factors that determine membrane selectivity

• A. Thickness of membrane• B. Size of molecule trying to penetrate• C. Lipid solubility• D. Electrical charge – like charges repell,

opposite charges attract.• E. Presence of active transport system

Cell organelles and their function

• Nucleus• Control center of the cell

Contains DNA within your chromosomes DNA serves as your genetic “blueprints”

• 1. Contains information for the synthesis of materials (protein).

• 2. Controls cell’s ability to reproduce.• 3. Nucleus contains the nucleolus, where RNA

is manufactured. RNA is important in protein synthesis.RNA carries information from DNA to cytoplasm.

Nucleus and nuclear envelope

Cell organelles and their function

• Endoplasmic reticulum• A system of membranous channels that serves

as a system of internal transport for the cell• ER is continuous with the nuclear envelope• Smooth ER (without ribosomes) is important in

the synthesis of lipids and carbohydrates• Smooth ER stores and releases CA++ for

muscle contraction • Rough ER contains ribosomes and is important

in protein synthesis

Endoplasmic reticulum

Cell organelles and their function

• Ribosomes serve as the site of protein synthesis

• Ribosomes may be found associated with ER. If so, the ER is called rough ER.

• Rough ER produces protein to be used outside the cell.

• Free ribosomes are found in the cytoplasm and are not associated with ER. Free ribosomessynthesize protein to be used in the cell.

Ribosomes-site of protein synthesis

Cell organelles and their function

• The Golgi complex or Golgi apparatus serves as a packaging body.

• Ex. The golgi complex wraps the protein produced by the ribosome in a membrane bound package for release to the outside of the cell = exocytosis

Golgi Complex or Apparatus

Cell organelles and their function

• Mitochondria serve as the “powerhouse” of the cell.

• Mitochondria are a major source of energy for the cell

• Cellular respiration takes place in the mitochondria to produce energy in the form of ATP.

• Active cells (cardiac) contain more mitochondria than inactive (skin) cells.

• When you work out regularly, you increase the number of mitochondria.

Mitochondria

Cell organelles and their function

• Lysosomes contain digestive enzymes.• Lysosomes are nick named the “garbage

disposal of the cell”.• Why have lysosomes?• 1. Cell parts become worn out and are

disposed of by lysosomes.• 2. When phagocytes eat bacteria,

lysosomes will digest them.

Cell organelles and their function

• Coordination of cell organelles.• Understanding the process of protein

synthesis will help you to remember the function of all of the cell organelles.

• A quick review of protein synthesis (making protein).

Protein Synthesis:Coordination of cell organelles

1. Blueprint for protein synthesis in DNA of nucleus.2. mRNA carries DNA message to cytoplasm via ER to

ribosome where protein is manufactured.3. Protein moves through ER to Golgi complex where

protein is packaged in a membrane and excreted to the outside of the cell through the cell membrane = exocytosis.

4. Where does the energy come from? Mitochondriaand ATP.

5. During the process cell parts may become worn out and digested by the lysosome.(Construction site analogy)

Cell Structurew/DNA

w/RNA