ch 2 - cells, enzymes, cell signaling - vertebrate...

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Chapter 2: Cells and Cell Processes

I. Cells A. Membranes B. Epithelia

II.  Metabolism III.  Enzymes IV.  Cell Signaling

I. Cells A. Membranes:

Control and regulate movement of substances across and between body regions, organs, etc.


Cell membrane structure 1.   Phospolipids 2.  Proteins 3.  Carbohydrates

Phospholipids •  Primary component of cell membrane –  Made up of lipids (fats) and phosphates –  Provides barrier at cell membrane

Phospholipids •  Bilayer structure is due to polarity and

hydrophilic properKes of phospolipid structure

Phospholipids •  Bilayer chemical composiKon is highly diverse –  Affects cell membrane properKes

•  Membrane fluidity (rigidity) •  Saturated tails have NO

double bonds •  Unsaturated tails have

one or more double bonds

Double bonds = Fluidity

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Phospholipids •  Bilayer chemical composiKon is highly diverse –  Affects cell membrane properKes

•  Membrane fluidity (rigidity)

•  Phospoholipids become sKffer at lower temps •  Animals living in low

temperatures have evolved more unsaturated tails

Cell membrane structure 1.  Phospolipids 2.   Proteins 3.  Carbohydrates

Proteins •  Interspersed among the phospholipid bilayer

Proteins 1.  Transmembrane proteins (span the bilayer)

have hydrophobic and hydrophilic parts 2.  Integral proteins are associated with one side

Proteins •  5 funcKonal protein types define what cell

membrane can do –  Not mutually exclusive

Cell membrane structure 1.  Phospolipids 2.  Proteins 3.   Carbohydrates

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Carbohydrates 1.  AVachment sites for proteins –  Usually occur in combinaKon with proteins

2.  Cell recogniKon sites used in cell signaling –  Hydrophillic – located on membrane surface


II.  Metabolism III.  Enzymes IV.  Cell Signaling


Epithelia Epithelia: Sheet of cells that covers body surface or organ or lines a cavity

•  Separates internal and external environments or regions of the body

Epithelia

•  FUNCTION: Control and/or mediate movement of substances across membrane

Epithelia: Sheet of cells that covers body surface or organ or lines a cavity

Epithelia structure 1. IntesBnal epithelia •  Microvilli: Increase absorpKon/secreKon

•  Can have mulKple cell types

2. Tubules/Follicles •  Blood vessels, kidneys •  Apical surface faces in; basal membrane out

Epithelial juncKons

1.  Tight juncKons 2.  Septate juncKons 3.  Desmosome 4.  Gap juncKons

•  Epithelial cells not bonded to one another •  JuncKons between cells regulate transport of

soluKons across membrane •  Permeability largely due to size of solute

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Epithelia •  Ions, nutrients, water, etc. pass through

epithelia using one of two paths I. Cells A. Membranes B. Epithelia

II.   Metabolism III.  Enzymes IV.  Cell Signaling


“Set of processes by which cells and organisms acquire, rearrange, and release energy in ways that sustain life”

Metabolism Metabolism

Nitrogen metabolism: Conversion of Nitrogen

from food into proteins and waste products (urea)

Energy metabolism: How energy is acquired, used, and transformed in the body

Two types of metabolic reacKons:

Metabolism

Nitrogen metabolism: Conversion of Nitrogen

from food into proteins and waste products (urea)

Energy metabolism: How energy is acquired, used, and transformed in the body

Two types of metabolic reacKons:

1.  Catabolic: Energy is RELEASED as chemicals broken down •  DestrucKve process

2.  Anabolic: Energy is USED to synthesize chemicals •  ConstrucKve process

Chapter 2: Cells, Enzymes, and Cell Signaling


II.  Metabolism III.   Enzymes IV.  Cell Signaling

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Enzymes •  Proteins that control metabolic reacKons

1.  Catalyze (speed up) reacKons 2.  Regulate reacKons (alters physiological

capabiliKes)

•  Most physiological processes will NOT proceed without appropriate enzymes –  Cells must

synthesize their own enzymes

Enzymes •  Only catalyzes or regulates reacKons with

substances to which it is bonded: enzyme-‐substrate complex

Enzymes as catalysts •  CATALYST: Molecule that accelerates a

reacKon, without being altered itself •  Note that Enzyme emerges unaltered!

Enzymes as catalysts •  ReacKon rate determined by:

1.  Amount of enzyme and substrate available

•  ReacBon rate/velocity: Amount of substrate converted to product per unit Kme


1.  Amount of enzyme and substrate available 1.  Substrate concentraKon low, relaKve to enzyme

2.  As E-‐S complexes form, rate slows •  Fewer free

substrate molecules 3.  When all enzymes

“used”, reacKon reaches Vmax OR Maximum Velocity

•  CatalyBc effecBveness: Extent to which enzyme lowers the acKvaKon energy required for reacKon


1.  Amount of enzyme and substrate available 2.  Enzyme’s catalyKc effecKveness

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•  Enzymes and substrates don’t always bond when come into contact


1.  Amount of enzyme and substrate available 2.  Enzyme’s catalyKc effecKveness 3.  Enzyme-‐substrate affinity

Enzymes as regulators 1.  Speed chemical reacKons 2.   Regulate chemical reacBons •  Synthesizing specific (new and/or different)

enzymes

Denaturing of enzyme and proteins •  Physiological stressors can denature proteins –  Can disrupt and/or halt their funcKon –  High temperature, low O2, toxic chemical

exposure

•  Molecular chaperones correct this damage –  Heat-‐shock

proteins in snails and mussels on clear days at low Kdes


•  Take aVendance!!

Enzymes as regulators 1.  Speed chemical reacKons 2.   Regulate chemical reacBons •  Synthesizing specific (new and/or different)

enzymes •  Changing catalyKc properKes of exisKng

enzymes

Enzymes operate at all Kme scales

Mediated by exisKng enzymes Mediated by synthesizing new enzymes Genes coding for specific enzymes adapt

to changing environment

Enzymes synthesized at different Kme intervals during development

CatalyKc acKvity of some enzymes

fluctuate throughout the day

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II.  Metabolism III.  Enzymes IV. Cell Signaling

Cell signaling

•  Coordinate cell funcKons throughout the body •  CommunicaKon

between cells necessary for all cellular funcKons

This looks complicated....

Cell signaling •  Receptor proteins in cell membrane control transfer of specific molecules

Cell signaling: Receiving signals •  Starts when ligand binds with receptor protein – Ligand: any molecule that bonds with a receptor protein

– Receptor site: where that bond occurs •  Four types of receptors

1.  Ligand-‐gated channels 2.  G protein-‐coupled 3.  Enzyme/enzyme-‐linked 4.  Intracellular

1. Ligand-‐gated channel •  Protein is both receptor and channel

Video

1. Ligand-‐gated channel •  Protein is both receptor and channel •  Channel opens in presence of ligand

Video

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2. G-‐protein coupled receptors 1.  Protein receptor ac/vates a G-‐protein aner

binding to ligand (1st messenger) 2.  G-‐protein + enzyme (or other membrane

protein) à disKnct signaling compound (2nd messenger)

Molecules DO NOT pass through cell membrane

video

3. Enzyme/enzyme-‐linked receptors •  Cell membrane proteins are also enzymes

•  Molecules DO NOT pass through cell membrane

•  Binding with ligand triggers acKvaKon of catalyKc site – Produces 2nd messenger

4. Intracellular receptor •  Receptor proteins inside the cell

•  Only small ligands that can diffuse through membrane

•  Intracellular process proceeds normally – E-‐S complexes formed

ch 2 - cells, enzymes, cell signaling - vertebrate...

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