The working cell

1
Chapter 5

• The working cell

2
Cellular energy

• Forms
• Kinetic
• Potential
• Energy of cells is ATP
• Energy lies in covalent bonds between P groups

3
Energy

• Exergonic
• Releases energy
• Endergonic
• Intakes energy (required energy)
• These reactions are coupled in energy coupling
  where exergonic reactions drive endergonic
  reactions

4
ATP

• Drives reactions via phosphorylation
• Transfer of a phosphate group to make molecules
  more reactive

Figure 5.4B
5
ATP

• P groups are negatively charged and crowded
  together
• Repulsion creates unstable bonds
• Broken via hydrolysis reaction
• As bonds break, 1 P leaves and ATP becomes ADP
  energy is released
• Released P goes to another molecule
• Transfer of P phosphorylation

6
Begin a chemical reaction

• Reactants must absorb some energy
• Energy of activation (EA)
• Enzymes can lower EA

7
Enzymes help begin chemical reactions

• Enzymes that lower EA are catalysts
• Decrease the EA needed to begin a reaction

8
Specificity

• Specific enzymes catalyze specific reactions
• Shape determines which chemical reaction an
  enzyme catalyzes
• Substrate
• Specific reactant an enzyme acts upon
• Active site
• Region of enzyme where substrate fits
• Active sites fit only specific substrates

9
How Enzymes Catalyze Reactions
Substrate(sucrose)
Active site
Substrate binds to enzyme with induced fit
Enzyme(sucrase)
Glucose
Fructose
H2O
Figure 5.6
10
Factors Influence Enzymes

• Temperature, pH, salinity
• Affect shape of the enzyme
• Optimal temperature
• Cofactors
• Non-protein helper
• Inorganic
• Ex zinc, iron, copper
• Coenzyme
• Organic
• Ex vitamin

11
Inhibitors Interfere with an Enzymes Activity

• Competitive inhibitor
• Noncompetitive inhibitor
• Feedback inhibition

12
Phospholipid bilayer

• Selectively permeable
• Imbedded proteins
• Fluid mosaic of phospholipids and proteins

13
Membrane Proteins

• Structural
• Cell-cell recognition
• Junction forming
• Receptors
• Enzymes
• Signal transduction
• Transport

14
Functions of membrane proteins
Enzymes Receptors for messages Transport
of substances
15

• The membrane is a fluid mosaic of phospholipids
  and proteins

Figure 5.12
16
In and Out of Cells

• Diffusion
• Passive transport
• Concentration gradient

17
Lipids
Plasma membrane (lipid bilayer)
18
In and Out of Cells

• Facilitated diffusion
• Small nonpolar molecules diffuse easily across
  the membrane
• Larger or polar molecules do not easily diffuse
• Transport proteins provide passage across
  membranes

19
Fructose
Plasma membrane
Transport protein
20
In and Out of Cells

• Osmosis
• Diffusion of water across a membrane
• Water travels from a solution of lower solute
  concentration to one of higher solute
  concentration

Solutemolecule
H2O
Selectivelypermeablemembrane
Watermolecule
Solute molecule with cluster of water molecules
Net flow of water
21
Plasma membrane
Transport protein
Water molecules
22
Balance

• Water balance between cells and their
  surroundings is crucial to organisms
• Osmosis causes cells to shrink in hypertonic
  solutions and swell in hypotonic solutions

Figure 5.17
23
In and Out of Cells

• Cells expend energy for active transport
• Transport proteins can move solutes against
  concentration gradient

Figure 5.18
24
In and Out of Cells

• Exocytosis and endocytosis transport large
  molecules
• Exocytosis
• Export material from cell
• Endocytosis
• Take into cell

Figure 5.19A
25
Types of Endocytosis

• Phagosytosis
• Cellular eating
• Pinocytosis
• Cellular drinking
• Receptor-mediated endocytosis
• Specific molecules

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