Chapter 3 - Cells: The living units (part a). Just as bricks and timbers are the structural units of a house, cells are the structural units of all living things, from one-celled “generalists” like amoebas to complex multicellular organisms such as humans, dogs, and trees. The human body has 50 to 100 trillion of these tiny building blocks. This chapter focuses on structures and functions shared by all cells.
Trang 1Cells: The Living Units
Trang 2 The cell is the smallest structural and
functional living unit
Organismal functions depend on individual and collective cell functions
Biochemical activities of cells are dictated by their specific sub cellular structures called organelles
Trang 3
Over 200 different types of human cells
Types differ in size, shape, subcellular components, and functions
Trang 4Copyright © 2010 Pearson Education, Inc.
Fibroblasts
Erythrocytes
Epithelial cells
(d) Cell that fights disease
Macrophage
Figure 3.1
Trang 5 All cells have some common structures and functions
Trang 6Copyright © 2010 Pearson Education, Inc. Figure 3.2
Secretion being released from cell
by exocytosis Peroxisome
Ribosomes
Rough endoplasmic reticulum
Nucleus
Nuclear envelope Chromatin
Golgi apparatus
Nucleolus Smooth endoplasmic
Trang 7 Bimolecular layer of lipids and proteins in a constantly changing fluid mosaic
Plays a dynamic role in cellular activity
Separates intracellular fluid (ICF) from
extracellular fluid (ECF)
◦ Interstitial fluid (IF) = ECF that surrounds cells
Trang 8Copyright © 2010 Pearson Education, Inc. Figure 3.3
Integral proteins
Extracellular fluid (watery environment)
Cytoplasm (watery environment)
Polar head of phospholipid molecule Glycolipid
Cholesterol
Peripheral proteins
Bimolecular lipid layer containing proteins
Inward-facing layer of
phospholipids
facing layer of phospholipids
Outward-Carbohydrate
of glycocalyx
Glycoprotein
Filament of cytoskeleton
Nonpolar tail of phospholipid molecule
Trang 101. Transport
2. Receptors for signal transduction
3. Attachment to cytoskeleton and extracellular
matrix
Trang 11Copyright © 2010 Pearson Education, Inc. Figure 3.4a
A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a
particular solute Some transport proteins (right) hydrolyze ATP as an energy source
to actively pump substances across the membrane.
(a) Transport
Trang 12Copyright © 2010 Pearson Education, Inc. Figure 3.4b
A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such
as a hormone The external signal may cause a change in shape in the protein that initiates a chain of chemical
reactions in the cell.
(b) Receptors for signal transduction
Signal
Receptor
Trang 13Copyright © 2010 Pearson Education, Inc. Figure 3.4c
Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins Others play a role in cell movement or bind adjacent cells
together.
(c) Attachment to the cytoskeleton and extracellular matrix (ECM)
Trang 144. Enzymatic activity
5. Intercellular joining
6. Cellcell recognition
Trang 15Copyright © 2010 Pearson Education, Inc. Figure 3.4d
A protein built into the membrane may
be an enzyme with its active site exposed to substances in the adjacent solution In some cases, several
enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here.
(d) Enzymatic activity
Enzymes
Trang 16Copyright © 2010 Pearson Education, Inc. Figure 3.4e
Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other
cell-to-cell interactions.
CAMs
(e) Intercellular joining
Trang 17Copyright © 2010 Pearson Education, Inc. Figure 3.4f
Some glycoproteins (proteins bonded
to short chains of sugars) serve as identification tags that are specifically recognized by other cells.
(f) Cell-cell recognition
Glycoprotein
Trang 18 Plasma membranes are selectively permeable
Some molecules easily pass through the
membrane; others do not
Trang 21 Simple diffusion
Carriermediated facilitated diffusion
Channelmediated facilitated diffusion
Osmosis
Trang 22 Nonpolar lipidsoluble (hydrophobic) substances diffuse directly through the phospholipid bilayer
Diffusion is the movement of solutes from a
solution of higher concentration to that of a lower concentration
PLAY Animation: Diffusion
Trang 23Copyright © 2010 Pearson Education, Inc. Figure 3.7a
Extracellular fluid
soluble solutes
Lipid-Cytoplasm
(a) Simple diffusion of fat-soluble molecules
directly through the phospholipid bilayer
Trang 24 Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel
Trang 25 Transmembrane integral proteins transport
specific polar molecules (e.g., sugars and amino acids)
Binding of substrate causes shape change in
carrier
Trang 26Copyright © 2010 Pearson Education, Inc. Figure 3.7b
Lipid-insoluble solutes (such as sugars or amino acids)
(b) Carrier-mediated facilitated diffusion via a protein
carrier specific for one chemical; binding of substrate causes shape change in transport protein
Trang 27 Aqueous channels formed by transmembrane proteins selectively transport ions or water
Trang 28Copyright © 2010 Pearson Education, Inc. Figure 3.7c
Small insoluble solutes
lipid-(c) Channel-mediated facilitated diffusion
through a channel protein; mostly ions selected on basis of size and charge
Trang 29 Movement of solvent (water) from a solution of low concentration to that of a higher
Trang 30Copyright © 2010 Pearson Education, Inc. Figure 3.7d
Water molecules
Lipid billayer
Aquaporin
(d) Osmosis, diffusion of a solvent such as
water through a specific channel protein (aquaporin) or through the lipid bilayer
Trang 31 Water concentration is determined by solute
concentration because solute particles displace water molecules
Osmolarity: The measure of total concentration of solute particles
When solutions of different osmolarity are
separated by a membrane, osmosis occurs until equilibrium is reached
Trang 32Copyright © 2010 Pearson Education, Inc. Figure 3.8a
(a) Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions Fluid volume remains the same in both compartments.
Left compartment:
Solution with lower osmolarity
Right compartment:
Solution with greater osmolarity
Membrane
H 2 O Solute
Solute molecules (sugar)
Both solutions have the same osmolarity: volume unchanged
Trang 33Copyright © 2010 Pearson Education, Inc. Figure 3.8b
(b) Membrane permeable to water, impermeable to solutes
Both solutions have identical osmolarity, but volume of the solution on the right is greater because only water is
free to move
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
Left compartment
Right compartment
Membrane
Solute molecules (sugar)
H 2 O
Trang 34 When osmosis occurs, water enters or leaves a cell
Change in cell volume disrupts cell function
PLAY Animation: Osmosis
Trang 35 Tonicity: The ability of a solution to cause a cell to shrink or swell
Trang 36Copyright © 2010 Pearson Education, Inc. Figure 3.9
Cells retain their normal size and
shape in isotonic solutions (same
solute/water concentration as inside
cells; water moves in and out).
Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration
of solutes than are present inside
the cells).
Cells take on water by osmosis until they become bloated and burst (lyse)
in a hypotonic solution (contains a lower concentration of solutes than are present in cells).