Transcript Lecture 4 - A tour through the cell

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 6
A Tour of the Cell
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Cells: The Fundamental Units of Life
• first cell observed – Robert Hooke in
1665
•
•
thin slices of bottle cork
saw a network of “cells” that a monk would live
in
• first living cell (Spirogyra) observed by
Anton van Leeuwenhoek in 1674
•
also described bacteria he found in his mouth
(1676)
Anton van Leeuwenhoek
Cells: The Fundamental Units of Life
• the cell is the simplest collection of matter
that can be alive
• the Cell Theory:
• 1. all organisms are made of at least one
type of cell
• 2. all cells come from pre-existing cells
by this cell dividing in two
• 3. the cell is the basic, fundamental
unit of life
• attributed to: Theodor Schwann, Matthias
Jakob Schleiden, and Rudolf Virchow
Concept: Eukaryotic cells have internal membranes that
compartmentalize their functions
• the basic structural and functional unit of every organism is
the cell
• two types of cells: prokaryotic or eukaryotic
• protists, fungi, animals, and plants all consist of eukaryotic
cells
Cells
• Basic features of all cells
– Plasma membrane
– Semifluid substance called cytoplasm
– organized DNA in the form of Chromosomes (carry
genes)
– Ribosomes (make proteins)
Comparing Prokaryotic and Eukaryotic
Cells
• Prokaryotic cells:
– no nucleus
– DNA in a region of the
cytoplasm called the nucleoid
– no membrane-bound
organelles
– a Cytoplasm bound by the
plasma membrane
– smaller ribosomes
• Eukaryotic cells
– membrane – bound
nucleus containing DNA
– membrane-bound
organelles
– a Cytoplasm in the region
between the plasma
membrane and nucleus
– larger ribosomes
The Eukaryotic Cell
• 1. Plasma membrane
• 2. Nucleus
• 3. Cytoplasm
– a. cytosol
– b. cytoskeleton
• 4. Cytoplasmic organelles
– membrane-bound
– non-membrane bound
Plants and fungus have a Cell Wall outside of the plasma
membrane
– not the same composition
The Plasma Membrane
• the plasma membrane is a semipermeable barrier
– allows sufficient passage of oxygen,
nutrients, and waste to service the
volume of every cell
• the general structure of a
biological membrane is a double
layer of phospholipids
– known as a phospholipid bilayer
– membrane proteins embedded within
it or found attached to one layer
Outside of cell
Inside of cell
0.1 m
(a) TEM of a plasma
membrane
Carbohydrate side chains
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
The Cytoplasm
• Comprised of
– 1. The cytosol
– 2. The cytoplasm
• Cytoskeleton = a“skeleton” of
protein filaments found
prokaryotic and eukaryotic cells
• Cytosol = intracellular fluid of the
prokaryotic or eukaryotic cell
The Cytosol
• also known as the intracellular fluid or ICF
– about 55% of the cell’s volume
– about 70-90% water PLUS
•
•
•
•
•
•
ions
dissolved nutrients – e.g. glucose
soluble and insoluble proteins
waste products
macromolecules and their components - amino acids, fatty acids
ATP
• unique composition with respect to extracellular fluid (ECF)
•
fluid found outside of a cell
The Eukaryotic Nucleus: Information Central
• the nucleus contains most of the eukaryotic cell’s genes and is usually the most
conspicuous organelle
• the nuclear envelope encloses the nucleus, separating it from the cytoplasm
– not found in prokaryotic cells – so NO nucleus in prokaryotic cells
• the nuclear envelope is comprised of two phospholipid bilayers
• the nucleolus is located within the nucleus and is the site of ribosomal
synthesis
– a prominent dark region inside the nucleus
• nuclear pores exist for import and export
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Rough ER
Pore
complex
Ribosome
Close-up
of nuclear
envelope
Chromatin
Eukaryotic DNA: Chromatin & Chromosomes
histone
DNA helix
nucleosome
-
organized form of DNA in the nucleus = chromatin
described as “beads on a string” model
DNA helix is wrapped around complexes of proteins called histones
the histone-DNA complex is called a nucleosome
described by Roger Kornberg – Nobel Prize 2006
Eukaryotic DNA: Chromatin & Chromosomes
• eukaryotic DNA needs to be condensed when the cell divides
• done just after the cell “copies” its DNA before mitosis
• cell “compacts” its chromatin into a duplicated chromosome
– histones play an important role
Membranous Organelles
•surrounded by one or two phospholipid bilayers that
are similar to the plasma membrane
•major functions of the membranous organelles
•1. protein synthesis – ER and Golgi
•2. energy production – mitochondria
•3. waste management – lysosomes & peroxisomes
1. Endoplasmic reticulum (ER) = multiple membrane-bound
compartments called cisterna (plural = cisternae)
-often attached to the nucleus
-responsible for:
1. protein synthesis
2. lipid & phospholipid synthesis
3. calcium storage
-two types: Rough ER vs. Smooth ER
-Rough ER (RER) – ribosomes “docked” onto their surface  protein synthesis
-Smooth ER (SER) – no ribosomes: lipid synthesis & calcium storage
2. Golgi Apparatus = multiple stacks of cisternae next to the ER
-described by Camillo Golgi in 1897
-responsible for:
1. protein modifications – sugar addition, trimming
2. protein sorting and targeting
3. Mitochondria
-singular = mitochondrion
-surrounded by a two phospholipid
bilayers
• an outer mitochondrial
membrane
• an inner mitochondrial
membrane
• a fluid-filled space = matrix
-the inner membrane is folded into folds called cristae
-these increase the membrane surface area for the enzymes of
ATP synthesis (via Oxidative phosphorylation)
4. Lysosomes = “garbage disposals”
-dismantle debris, eat foreign invaders/viruses internalized by
the cell
-cell biologists not really sure exactly how the lysosome forms
-contain powerful enzymes to breakdown substances into their
component parts
-these enzymes are collectively known as acid hydrolases
e.g. nucleases = breakdown RNA & DNA into nucleotides
e.g. proteases = breakdown proteins into amino acids
5. Peroxisomes: found in all cells but abundant in liver and kidney
cells
-only identified in 1954
-major function is breakdown of fatty acids
- but this reaction generates hydrogen peroxide (H2O2)
- so peroxidases contain an enzyme (called catalase) that catalyzes
the breakdown of the H2O2 into H2O and O2
Non-membranous Organelles
A. Centrioles: short cylinders of a protein called tubulin
- 9 microtubule triplets called a 9+0 array (9 peripheral triplets, 0 in the
center)
-found in cells capable of division (in an area of the cell called the
centrosome)
-has a role in mitosis - spindle and chromosome alignment
-duplicate just prior to the onset of mitosis
-migrate to opposite ends of the replicating cell
-mitotic spindle grows in between
centriole
spindle
B. Cilia & Flagella
• cilia = projections off of the plasma membrane of
eukaryotic cells
• flagella = larger cilia
• made of hollow “straws” of tubulin called
microtubules
• beat rhythmically to transport material – power &
recovery strokes
• found in linings of several major organs covered with
mucus where they function in cleaning
• e.g. trachea, lungs
Trachea
Tubulin in a microtubule
B. Cilia & Flagella
• cilia and flagella = 9+2 array  9 doublets around the
periphery + 2 singlets in the center of the cilia
C. Ribosomes: Protein Factories
• Ribosomes are particles made of ribosomal RNA (rRNA) and
protein
• comprised of two subunits
– large
– small
• ribosomes carry out protein synthesis
0.25 m
Free ribosomes in cytosol
Endoplasmic reticulum (ER)
Ribosomes bound to ER
Large
subunit
Small
subunit
TEM showing ER and
ribosomes
Diagram of a ribosome