Download 3- Cell Structure and Function How do things move in

3- Cell Structure and Function
How 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 energy
expenditure by the cell and include:
1- Active Transport
2- Vesicular Transport
A. Endocytosis
1. Pinocytosis
2. Phagocytosis
3. 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 cell
to move molecules from a [Low] to [High]
against a concentration gradient.
[High]
[Low]
•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.
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 pump
or 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+
By Active Transport
By
High Na+
Diffusion
High
Na+
Na+
Na+ - K+
Transport
Protein
Low
Low
Na+
Na+
Cell
Active Transport of K+
By Active Transport
By
Diffusion
Low
K+
Low K+
K+
Na+ - K+
Transport
Protein
High
High K+
K+
Cell
Active Transport of K+ and Na+
Low K+
High Na+
Na+ - K+
Transport
Na+ - K+
Transport
Protein
Protein
Low
Na+
High K+
Cell
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 ProcessesVesicular transport
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•
•
•
There are 3 types of endocytosis
1. Phagocytosis = cell eating (solids)
2. Pinocytosis = cell drinking (liquids)
3. Receptor mediated endocytosis
Active ProcessesVesicular 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 ProcessesVesicular 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 ProcessesVesicular 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
Hydrophobic “water-fearing” tail
= charged
= 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
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•
•
•
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 ribosomes
synthesize protein to be used in the cell.
Ribosomessite 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.
2.
3.
4.
5.
Blueprint for protein synthesis in DNA of nucleus.
mRNA carries DNA message to cytoplasm via ER to
ribosome where protein is manufactured.
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.
Where does the energy come from? Mitochondria
and ATP.
During the process cell parts may become worn out
and digested by the lysosome.
(Construction site analogy)
Cell Structure
w/DNA
w/RNA