Download Chapter 3 Cells

The Cellular Level
of Organization
General Cell Structures
• Plasma membrane or cell membrane
- forms the cell’s outer boundary
- separates the cell’s internal environment from the outside
environment
- is a selective barrier (selective permeability)
- plays a role in cellular communication
• Cytoplasm
- everything between the plasma membrane and the nucleus
- cytosol: fluid portion
- organelles: subcellular structures with specific functions
• Nucleus
- large organelle that chromosomes, each of which consists of
a single molecule of DNA and associated proteins
- a chromosome contains thousands of hereditary units
called genes
Typical Cell
Plasma Membrane
Animation: Membrane Functions
Selective Permeability of Membrane
• Lipid bilayer
– permeable to nonpolar, uncharged molecules
• oxygen, CO2, steroids
– permeable to water which flows through gaps that
form in hydrophobic core of membrane as
phospholipids move about
• Transmembrane proteins act as specific channels
– small and medium polar & charged particles
• Macromolecules unable to pass through the
membrane
– vesicular transport
Membrane Proteins
Membrane
Proteins
Ion channels
Carriers
Receptors
Membrane
Proteins
Enzymes
Linkers
Cell identity markers
Transport Across the Membrane
Diffusion
Transport Across the Membrane
Diffusion
Transport Across the Membrane
Channel-Mediated Diffusion
Facilitated Diffusion
Transport Across the Membrane
Carrier-Mediated Diffusion
Transport Across the Membrane
Osmosis
Effects of Tonicity
Active Transport
Secondary Active Transport
Antiporters and Symporters
Transport in Vesicles




Vesicle - a small spherical sac formed by budding off from a
membrane
Endocytosis - materials move into a cell in a vesicle formed
from the plasma membrane
three types: receptor-mediated endocytosis
phagocytosis
bulk-phase endocytosis (pinocytosis)
Exocytosis - vesicles fuse with the plasma membrane, releasing
their contents into the extracellular fluid
Transcytosis - a combination of endocytosis and exocytosis
Copyright © John Wiley & Sons, Inc. All rights reserved.
ReceptorMediated
Endocytosis
Phagocytosis
Endocytosis
Bulk-phase endocytosis
Transport

Transport Across the Plasma Membrane
Animation
Copyright © John Wiley & Sons, Inc. All rights reserved.
Transport
of
Materials
Cytoplasm
Cytoplasm - 2 Components
1. Cytosol - intracellular fluid, surrounding the organelles
- The site of many chemical reactions
- Energy is usually released by these reactions.
- Reactions provide the building blocks for cell maintenance,
structure, function and growth.
2. Organelles
- Specialized structures within the cell
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cytoskeleton
• Network of protein filaments
throughout the cytosol
• Provides structural support for
the cell
• Microfilaments
– thinnest filaments (actin)
– locomotion & division
– support microvilli
• Intermediate filaments
– several different proteins
– anchor organelles
• Microtubules
– large cylindrical structures
(tubulin)
– flagella, cilia &
centrosomes
Centrosome

located near the nucleus, consists of two centrioles and
pericentriolar material
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cilia and Flagella
• Structure
– pairs of microtubules
– covered by cell
membrane
– basal body is centriole
responsible for initiating
its assembly
• Differences
– cilia
• short and multiple
– flagella
• longer and single
Cilia and Flagella
Copyright © John Wiley & Sons, Inc. All rights reserved.
Ribosomes
sites of protein synthesis
Endoplasmic
Reticulum
- network of membranes in the
shape of flattened sacs or
tubules
- Rough ER - connected to the
nuclear envelope, a series of
flattened sacs, surface is
studded with ribosomes,
produces various proteins
-Smooth ER - a network of
membrane tubules, does not
have ribosomes, synthesizes
fatty acids and steroids,
detoxifies certain drugs
Golgi Complex
• 3-20 flattened, curved membranous sacs called
cisterns
• Convex side faces ER & concave side faces
cell membrane
• Processes & packages proteins produced by
rough ER
Packaging by Golgi Complex
Lysosomes
•
•
•
•
Membranous vesicles
formed in Golgi complex
filled with digestive enzymes
digest foreign substances
Peroxisomes
–
–
–
–
smaller than lysosomes
form by division of preexisting peroxisomes
contain enzymes that oxidize organic material
part of normal metabolic breakdown of amino acids and fatty
acids
– oxidizes toxic substances such as alcohol and formaldehyde
– contains catalase which decomposes H2O2
Proteasomes
–continuously destroy unneeded, damaged, or faulty proteins,
found in the cytosol and the nucleus
Mitochondria
• Double membrane organelle
– central cavity known as
matrix
– inner membrane folds known
as crista
• surface area for chemical
reactions of cellular respiration
• Function
– generation of ATP
– “powerhouse of cell”
Nucleus
• Large organelle with
double membrane nuclear
envelope
• outer membrane
continuous with
rough ER
• perforated by waterfilled nuclear pores
(10X channel pore
size)
• Nucleolus
–spherical, dark bodies within the
nucleus (no membrane)
–site of ribosome assembly
Cell Parts
and Their
Functions
Protein Synthesis
Transcription
Translation
Protein
Elongation
Cell Cycle
DNA Replication
Mitosis and
Cytokinesis
Somatic Cell
Cycle
Meiosis
Mitosis
vs.
Meiosis
Cellular Diversity
•
The average adult has
nearly 100 trillion cells.
•
There are about 200
different types of cells.
•
Cells come in a variety of
shapes and sizes.
•
Cellular diversity permits
organization of cells into
more complex tissues
and organs.