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Biochem Chapter 5 notes, Summaries of Biochemistry

University of California - San DiegoBiochemistry
Prof. Nancy Guy

Notes for BIOCHEM classes for UCSD

Typology: Summaries

2025/2026

Uploaded on 05/10/2026

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Created by Brett Barbaro
Biochemistry: A
Short Course
Fourth Edition
CHAPTER 12
Membrane
Structure and
Function
Tym oc z ko • Berg • Gatto • Stryer
© 2019 Macmillan Learning
1
Created by Brett Barbaro
Chapter 12: Outline
12.1 Phospholipids and Glycolipids Form Bimolecular
Sheets
12.2 Membrane Fluidity Is Controlled by Fatty Acid
Composition and Cholesterol Content
12.3 Proteins Carry Out Most Membrane Processes
12.4 Lipids and Many Membrane Proteins Diffuse
Laterally in the Membrane
12.5 A Major Role of Membrane Proteins Is to Function as
Tran sp ort er s
THIS SECTION IS NOT DISCUSSED IN
DETAIL IN THE LECTURE
2
Created by Brett Barbaro
Characteristics of Membranes
1. Membranes are sheetlike structures, two molecules thick, that form
closed boundaries.
2. Membranes are composed of lipi ds and prot eins, ei ther of whi ch can
be decorated with carbohydrates.
3. Membrane lipids ar e small amphipathi c molecules that for m closed
bimolecular sheets that pr event the movement of polar or charged
molecul es.
4. Proteins serve to mitigate the impermeabi lity of membranes and
allow movement of molecules and inf ormation across the cell
membrane.
5. Membranes are flui d, noncoval ent assembl ies.
3
Created by Brett Barbaro
Section 12.1 Phospholipids and
Glycolipids Form Bimolecular Sheets
Learning objective 1: Identify the energetic force that
powers the formation of membranes.
•Phospholipids and glycolipids form lipid bilayers in
aqueous solutions.
•The formation of membranes is powered by the
hydrophobic effect.
4
pf3
pf4
pf5
pf8

Partial preview of the text

Download Biochem Chapter 5 notes and more Summaries Biochemistry in PDF only on Docsity!

Created by Brett Barbaro

Biochemistry: A

Short Course

Fourth Edition

CHAPTER 12

Membrane

Structure and

Function

Tymoczko • Berg • Gatto • Stryer

© 2019 Macmillan Learning

Created by Brett Barbaro

Chapter 12: Outline

12.1 Phospholipids and Glycolipids Form Bimolecular Sheets 12.2 Membrane Fluidity Is Controlled by Fatty Acid Composition and Cholesterol Content 12.3 Proteins Carry Out Most Membrane Processes 12.4 Lipids and Many Membrane Proteins Diffuse Laterally in the Membrane 12.5 A Major Role of Membrane Proteins Is to Function as Transporters THIS SECTION IS NOT DISCUSSED IN DETAIL IN THE LECTURE

Created by Brett Barbaro

Characteristics of Membranes

  1. Membranes are sheetlike structures, two molecules thick, that form closed boundaries.
  2. Membranes are composed of lipids and proteins, either of which can be decorated with carbohydrates.
  3. Membrane lipids are small amphipathic molecules that form closed bimolecular sheets that prevent the movement of polar or charged molecules.
  4. Proteins serve to mitigate the impermeability of membranes and allow movement of molecules and information across the cell membrane.
  5. Membranes are fluid, noncovalent assemblies.

Created by Brett Barbaro

Section 12.1 Phospholipids and

Glycolipids Form Bimolecular Sheets

Learning objective 1: Identify the energetic force that powers the formation of membranes.

  • Phospholipids and glycolipids form lipid bilayers in aqueous solutions.
  • The formation of membranes is powered by the hydrophobic effect.

Created by Brett Barbaro Electron Micrograph and Space-filling Model of a Phospholipid Bilayer Membrane 5 Created by Brett Barbaro Diagram of the Preparation of Glycine- Containing Liposomes 6 Created by Brett Barbaro Lipid Bilayers Are Highly Impermeable to Ions and Most Polar Molecules Learning objective 2: Explain why membranes are impermeable to most substances.

  • The ability of small molecules to cross a membrane is a function of its hydrophobicity.
  • Indole is more soluble than tryptophan in membranes because it is uncharged. Ions cannot cross membranes because of the energy cost of shedding their associated water molecules. 7 Created by Brett Barbaro Permeability Coefficients of Ions and Molecules in a Lipid Bilayer N 2 O 2 CO 2 NO some steroids 8

Created by Brett Barbaro Proteins Associate with the Lipid Bilayer in a Variety of Ways Proteins associate with the lipid bilayer in a variety of ways.

  • Integral membrane proteins are embedded in the hydrocarbon core of the membrane.
  • Peripheral membrane proteins are bound to the polar head groups of membrane lipids or to the exposed surfaces of integral membrane proteins.
  • Some proteins are associated with membranes by attachment to a hydrophobic moiety that is inserted into the membrane. 13 Created by Brett Barbaro Diagram of Integral and Peripheral Membrane Proteins 14 Created by Brett Barbaro Structure of Bacteriorhodopsin
  • Membrane-spanning α helices are a common structural feature of integral membrane proteins. hydrophobic residues in here hydrophilic residues out here hydrophilic residues out here 15 Created by Brett Barbaro Structure of Bacterial Porin
  • Other means of embedding integral membrane proteins is by using β strands to form a pore in the membrane or by embedding part of the protein into the membrane. Hydrophobic residues out here SIDE VIEW TOP VIEW Hydrophilic residues in here 16

Created by Brett Barbaro Diagram of the Attachment of Prostaglandin H 2 synthase-1 to the Membrane 17 Created by Brett Barbaro Section 12.5 A Major Role of Membrane Proteins Is to Function as Transporters

  • Transport proteins function as pumps or channels to facilitate the flow of small molecules across the cell membrane.
  • Passive transport or facilitated diffusion occurs when a molecule moves down its concentration gradient through a transport protein.
  • Protein pumps use energy to move a molecule against its concentration gradient in the process of active transport. 18 Created by Brett Barbaro The Na + – K +^ ATPase Is an Important Pump in Many Cells
  • The Na+–K+^ ATPase or Na+–K+^ pump uses the energy of ATP hydrolysis to simultaneously pump three Na+^ ions out of the cell and two K+^ ions into the cell against their concentration gradients. 19 Created by Brett Barbaro Diagram of Energy Transduction by Membrane Proteins 20

Created by Brett Barbaro The Structure of the Potassium Ion Channel Reveals the Basis of Ion Specificity

  • The potassium channel selectively and rapidly transports K+^ across the cell membrane. Larger ions are not transported because they are too big to enter the channel.
  • Smaller ions are excluded because they cannot interact with the selectivity filter. Such ions are small enough that the energy of desolvation cannot be compensated for by interactions with the selectivity filter. 25 Created by Brett Barbaro Diagram of a Path Through a Channel 26 Created by Brett Barbaro Diagram of the Selectivity Filter of the Potassium Ion Channel 27 Created by Brett Barbaro Diagram of the Energetic Basis of Ion Selectivity (Postassium) 28

Created by Brett Barbaro Diagram of the Energetic Basis of Ion Selectivity (Sodium) 29 Created by Brett Barbaro Quick Quiz 2 QUICK QUIZ 2 What determines the direction of flow through an ion channel? 30