Cell Structure and Function
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
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
An Idealized Animal Cell
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.
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.
Two Other Unique Features of Plant Cells
The central
vacuole may
occupy 90%
of a plant
cell.
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
Many Diseases are Caused by Lysosome Malfunction
Vacuoles
• Vacuole – saclike
structure that stores
materials such as
proteins, salts, water,
and carbohydrates
• Many plants have a
single, large vacuole
filled with liquid,
allowing for turgor
The Central Vacuole Controls Turgor Pressure
flaccid
turgid
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)
Cells In a Leaf
The Chloroplast
Think of the chloroplast as the solar panel of the plant cell.
Only plants have chloroplasts, but animals reap the benefits too.
Chloroplast
• Chloroplasts –
organelles that capture
the energy from
sunlight and convert it
into chemical energy in
a process called
photosynthesis
• Two membranes
• Plants and a few other
organisms contain
chloroplasts
Two Other Unique Features of Plant Cells
The central
vacuole may
occupy 90%
of a plant
cell.
A Consequence of Cell
Walls – the Great
Strength of Woody
Plants
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.
The cytoskeleton is a network of protein filaments that helps
the cell maintain it’s shape and aids in cell movement.
Type of filament
1. Microtubules
Shape
hollow tubes
2. Microfilaments
long, thin fibers
support/movement
Purpose
maintain shape and
act as railroad tracks
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
• Biologists use levels of organization to make it
easier to identify and classify the cells in a
particular organism.
• Levels of Organization
• 1 . Cells - division of labor for organism
• 2. Tissues- similar cells performing a particular
function
• 3. Organs- multiple tissues working together;
• 4. Organ systems- multiple organs working
together
• 5. Organism – living individual
Cells
Tissues
Organ
Organ System
Organism