Class notes
Biol 1103 Chapter 5-8 Notes
- Course
- BIOL 1013
- Institution
- Baton Rouge Community College
Detailed and comprehensive notes Chapter 5-8. *Essential Study Material!!
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Chapters 5-8 study guidesChapter 5 Membrane Structure, Synthesis, and Transport
5.1 Membrane Structure.
Describe the Fluid-Mosaic Model of Membrane Structure.
o Phospholipid Bilayer Components
Cell membrane is a fundamental and defining feature of cells, with the
hydrophilic phosphate head groups facing the aqueous environment on
the other side and the hydrophobic tails in the middle.
Amphipathic
Phospholipid molecules
Hydrophobic
(Water fearing) regions face in
Hydrophilic
(Water loving) regions face out
o Fluid-Mosaic Model
Mosaic of phospholipid, protein, and carbohydrate molecules
Fluid lipids and proteins move more relative to each other within
membrane
Two leaflets (halves of bilayer) asymmetrical
Identify the Three Different Types of Membrane Proteins.
o Transmembrane Proteins
Physically embedded in hydrophobic region of phospholipid bilayer
Integral membrane protein
o Lipid-Anchored Protein
Covalent attachment of lipid to amino acid within protein
Integral membrane protein
o Peripheral Protein
Non-covalently bound to
Integral membrane protein
Polar head groups of phospholipids
5.2 Fluidity Of Membranes.
Describe the Fluidity of Membranes.
o Semi-Fluid
Movement occurs in two directions
Lipids rotate
Phospholipids
Cholesterol
Proteins move
Typical phospholipid exchanges places with its neighbor 10 ^7 s^-1
CoreSKILL-> Predict How Changes in Lipid Composition Affect Membrane Fluidity.
o Lipid Composition Affects Fluidity by…
Length of phospholipid tails
Short = more fluid
Number of double bonds
More = more fluid
Unsaturated
Cholesterol for stabilization
Warm temp. – makes more rigid
Cold temp. - makes more fluid
, Proteins may be anchored
5.3 Synthesis Of Membrane Components In Eukaryotic Cells.
Outline the Synthesis of Lipids at the ER Membrane.
o 1
In the cytosol, fatty acids are activated by the attachment of a CoA
molecule
o 2
The fatty acids bond to glycerol-phosphate and are inserted into the
cytosol Inc. leaflet of the ER membrane via acyl transferase
o 3
The phosphate is removed by a phosphate enzyme.
o 4
A choline already linked to the phosphate its attached via choline
phosphatransferase.
o 5
Flippases transfer some of the phospholipids to the other leaflet
Explain How Transmembrane Proteins are Inserted into the ER Membrane.
o 1
A protein begins synthesis into the ER, and the ER signal sequence is
cleaved.
o 2
Polypeptide synthesis continues, a hydrophobic transmembrane
segment is made as the polypeptide is being threaded through the
channel
o 3
Polypeptide synthesis is completed and the transmembrane sequence
remains in the membrane
Describe the Process of Glycosylation and its Functional Consequences.
o Glycosylation
Process of covalently attaching a carbohydrate to a protein or lipid
Glycolipid
Carbohydrate to lipid
Glycoprotein
Carbohydrate to protein
N-Linked Glycosylation
Attachment of carbohydrate to nitrogen atom of asparagine side
chain
O-Linked Glycosylation
Addition of sugars to oxygen atom of serine or threonine side chains
Only in Golgi
o Process of Glycosylation
1
Prior to Glycosylation of a polypeptide, a group of 14 sugars is built
onto a lipid in the ER membrane
2
Oligosaccaride transferase moves the carbohydrate tree from the
lipid and transfers it to an asparagine in the polypeptide
3
Polypeptide synthesis is completed
5.4 Overview of Membrane Transport.
, Compare and Contrast Simple Diffusion , Facilitated Diffusion , Passive
Transport , And Active Transport.
o Passive Transport
Does not require energy
Solutes moves down or with [] gradient
Movement of bio chemicals and other atomic or molecular substances
across cell membrane via specific transmembrane integral proteins
Simple Diffusion
Diffusion of a solute through membrane without transport
protein
Substance moves from area of [high] to [low]
No energy required
Facilitated Diffusion
Movement of biochemical and other atomic or molecular
substances across cell membranes without the need of energy
input
Substance moves from area of [high] to [low]
o Active Transport
Requires energy to move substances across cell membranes
Substance moves from area of [low] to [high]
o Selectively Permeable
When a cell lets some things across the cell membrane but excludes
others
o Membrane Transport
The movement of particles of any substance so that they spread out
evenly into the available space
o Transmembrane Gradient
Protein channels and carrier proteins
Concentration Gradient
Amount of gradient difference in concentration from one area to
another
o Electrochemical Gradient
Usually for an ion that can move across a membrane
Describe the Process of Osmosis and how it Affects Cell Structure.
o Osmosis
Diffusion of water
Moves water from a higher concentration to a lower concentration
o Isotonic
Solute concentration outside equals the inside, no net movement,
animals like this
_[solute]=[solute] on either side of the membrane
o Hypertonic
Solute concentration is greater outside then inside
Cell shrinks or shrivels
Water becomes plasmolyze
3.5% solute
o Hypotonic
Solute concentration is greater inside than outside
Water enters the cell and it gets larger
Plants like this and animals don’t because they’ll explode
0.1% solute
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