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Cell Structure and Function
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Why Study Cell
Biology?
The key to every
biological
problem must
finally be sought
in the cell, for
every living
organism is, or at
some time has
been, a cell. E.B.
Wilson, 1925
Cells are Us
Cells are Us
Cilia on a protozoan
Sperm meets egg
Cells are Us
A person contains about 100 trillion cells.
That’s 100,000,000,000,000 or 1 x 1014
cells.
There are about 200 different cell types in
mammals (one of us).
Cells are tiny, measuring on average about
0.002 cm (20 um) across. That’s about
1250 cells, “shoulder-to-shoulder” per
inch.
Red and
white blood
cells above
vesselforming cells.
nerve cell
Discovery of the Cell
• Englishman Robert Hooke in 1665 used an
early compound microscope to look at cork
• What is cork?
– Plant material – therefore has plant cells
• Called them “cells” because they reminded
him of a monastery’s rooms, called cells
• Anton van Leeuwenhoek in 1674 observed
pond life in a microscope
The Cell Theory
The cell theory (proposed independently in 1838 and
1839) is a cornerstone of biology.
All organisms are composed of one or more cells.
Schleiden
Cells are the smallest living things.
Cells arise only by division of previously existing cells.
All organisms living today are descendents of an
ancestral cell.
Schwann
A Sense of Scale and Abundance – Bacteria on the Head of a Pin
Two Fundamentally Different Types of Cells
A prokaryotic cell
A eukaryotic cell
Us vs.
Them Eukaryotes
and
Prokaryotes
The Nucleus
• The nucleus (plural: nuclei) is a large
membrane-enclosed structure that contains
the cell’s genetic material in the form of
DNA.
• The nucleus controls many of the cell’s
activities.
• Eukaryotes are cells that contain nuclei.
• Prokaryotes are cells that do not contain
nuclei.
An Idealized Animal Cell
Eukaryotic Cells
• Eukaryotic cell can be likened to a factory
• There are many structure in eukaryotic
cells.
• These are called organelles – “little organs”
• Two major parts of cell:
– Nucleus
– Cytoplasm – portion of cell outside nucleus
Major Divisions of the Eukaryotic Cell
A rat liver cell (with color enhancement to show organelles)
It’s Crowded In There
An artist’s conception of the cytoplasm - the region of a cell
that’s not in the nucleus or within an organelle.
It’s Crowded
In There
A micrograph
showing
cytoskeleton
(red), ribosomes
(green), and
membrane (blue)
Animal and Plant Cells Have More
Similarities Than Differences
Cellular Anatomy
We’ll start by seeing what role these parts play in making and
moving proteins.
The Nucleus
• Contains nearly
all of cell’s DNA
– the instructions
for making
proteins
• Surrounded by
nuclear envelope
• Most cells have
one nucleus
• RBCs have 0
• Skeletal muscle
cells have many
Think of the nucleus as the cell’s
control center.
Two meters of
human DNA fits
into a nucleus
that’s 0.000005
meters across.
The Nucleus
• Granular material is called
chromatin – DNA bound
to protein
• When cell divides,
chromatin condenses to
form chromosomes which
pass genetic information
on to new cells
• Nucleolus - Dense region
of nucleus where
ribosomes are assembled
Ribosomes and the Endoplasmic Reticulum
Ribosomes
• Ribosomes – sites of protein assemblage
• Follow instructions from nucleus
The Rough Endoplasmic Reticulum
Functions:
Protein synthesis
(about half the cell’s
proteins are made
here).
Protein movement
(trafficking)
Protein
“proofreading”
Golgi Apparatus
• Proteins produced in
ER then move into
Golgi Apparatus.
• Function – modify,
sort, package proteins
• Proteins then
transported to
elsewhere in the cell
or outside the cell
The Lysosome
Functions:
Digesting food or
cellular invaders
Recycling cellular
components
Cell suicide –
programmed cell death
(The lysosome is not
found in plant cells)
Many Diseases are Caused by Lysosome Malfunction
The Mitochondrion
Think of the mitochondrion as the
powerhouse of the cell.
Both plant and animal cells contain
many mitochondria.
(Mitochondria is the
plural of mitochondrion)
Mitochondria
• Mitochondria – convert
chemical energy stored in
food into compounds the
cell can use
• Inner and outer membrane
• Inherited from mother
• Cells that need more
energy will have more
mitochondria (white meat
vs. dark meat)
The Cytoskeleton
The name is
misleading. The
cytoskeleton is the
skeleton of the cell, but
it’s also like the
muscular system, able
to change the shape of
cells in a flash.
An animal cell cytoskeleton
A Cytoskeleton Gallery
The
Cytoskeleton
in Action
A white
blood cell
using the
cytoskeleton
to “reach
out” for a
hapless
bacterium.
The Cytoskeleton in Action
Cilia on a protozoan
Beating sperm tail at fertilization
Smoker’s cough is due to destruction of cilia linking the airways.
Cell Membrane
• Forms outer boundary
of cell
• Separates contents from
environment
• Made mainly of lipids
and proteins
• Regulates movement
into and out of the cell
Membrane Structure
• Lipids consist of
phosphate heads that are
hydrophilic
• Tails consist of fatty acids
that are hydrophobic
• Two layers in all
• Proteins imbedded in and
on membrane
• Together they are called
the “Fluid Mosaic Model”
Membrane Proteins
• Channel proteins – go through membrane
and allow for passage into and out of cell
• Receptor proteins – receive information
from other cells (hormones)
• I.D. proteins – identify whose cells and
what type of cells
• Carrier protein – transmit material that is
too large into and out of cell (facilitated
diffusion)
Membrane Movements
• Equilibrium – when the
concentration of a solute is the
same throughout the system
• Diffusion – movement of solute
from high to low concentration
• Heat, size, concentration,
solubility all affect rate
• Osmosis – water diffusion
through a selectively permeable
membrane
Cellular Movements
• Facilitated Diffusion
– still diffusion (w/o
energy input) but must
have a carrier protein
to get through
• Think of needing to
have a ticket to go to a
concert
Cellular Movements
• Active Transport –
carrier-mediated
facilitated diffusion that
requires ATP
• Goes against the conc.
Gradient or from lo – hi
• Because particles are
going the “wrong way”
energy is required in the
form of ATP
Sodium – Potassium Pump
• Simultaneously carries
Na+ ions out of and K+
ions into the cell
• ATP provides energy to
move 3 sodium ions out
and 2 potassium ions in
against gradients
• Allows for normal
transmission of impulses
by nerve cells
Membrane Movements
• Endocytosis – engulf particle
into cell; nutrient acquistion
• Phagocytosis – “cell eating”;
endocytosis of large particles
such as bacteria; protective
mechanism
• Pinocytosis – “cell drinking”
gulping droplets of
extracellular fluid; routine
absorption
• Exocytosis – cell products
and waste released from cell
Variations of Cells
Largest Cell
Longest Cell
Cell Size Limitations
• Diffusion limits cell size
– Slow and inefficient over large areas
• DNA limits cell size
– Limit to how quickly DNA can be read
– Limit to # of proteins built/period of time
• Surface area to volume ratio limits cell size
– Volume increases faster than surface area
– Requires more nutrients, produces more waste, but
with relatively smaller surface area
Question
• Which one of these has the best ratio of surface area to cell
volume?
Cell Reproduction
• All cells in the world
today came from
preexisting cells (Cell
Theory)
• How does this happen?
• The cell cycle
Cell Life Cycle
• The cell life cycle is the
series of changes a cell goes
through from the time it
forms until it divides.
• Two major periods:
– Interphase – cell grows
and carries on metabolic
activities
– Cell Division – cell
reproduces itself
The Cell Cycle
• Interphase
– G1: Growth…
– S: Copy the DNA...
– G2: Growth…
• Mitosis
– Process which forms two
daughter cells.
Interphase
• Longest phase in cell cycle (90+% of time)
• Cell is very active
Plant Cell
Animal Cell
Mitosis
Step 1: Prophase
Chromosomes form
Chromosomes
• DNA when it is tightly packed.
Chromosomes appear just before a cell
reproduces.
– Formed from condensed chromatin
Prophase
•
•
•
•
•
Two halves called sister chromatids
Center region called centromere
Nucleus disappears
Centrioles migrate to opposite poles
Spindle fibers made of microtubules form between
centrioles
Chromosomes line up
Metaphase
• Chromosomes attached to spindle fibers at centromeres
• Pulled to middle (equator) by spindle fibers
• Each sister chromatid has own fiber
Chromosomes begin to pull apart
Chromosomes at opposite ends
Telophase
• Nucleus reforms
• Chromosomes unwind
into Chromatin
• Spindle breaks down
• Nucleolus reappears
Cell splits into two cells.
Control of the Cell Cycle
• Proteins called Cyclins interact with enzymes to
become activated
• These proteins control the cell cycle
Cancer: Uncontrolled Cell Growth
• Cancer – malignant growth
resulting from uncontrolled
cell division.
• Change in one or more genes
that produce Cyclin
• Cancerous cells form masses
of called tumors
• 2nd leading cause of death in
US
• Affects any tissue in body
Causes of Cancer
– Environmental Conditions (carcinogens)
• Affect Genes: segment of DNA responsible for production of a protein
• Failure to produce enzymes
• Overproduction of enzymes
– Viral Infection
Some of the many cancers caused by
smoking
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Some cancers associated with
smoking
Lung Cancer
Head and Neck Cancer
Mouth Cancer
Esophageal Cancer and Throat Cancer
Pancreatic Cancer
Colorectal Cancer
Stomach Cancer
Bladder Cancer
Cervical Cancer
Breast Cancer
Colorectal Cancer
Kidney Cancer
Myeloid Leukemia
Liver cancer
Encyclopedia of Cancer by R.N. Tamara L. Brown
http://www.ash.org.uk/html/factsheets/html/fact04.html
Chemicals included in cigarettes
Cancer Prevention
• Diets low in fat and high in fiber content
• Vitamins and minerals may also prevent cancer
• Daily exercise and controlling environmental
conditions help as well.
• DON’T
SMOKE!