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Cell Biology - Class 02
The in-depth study of human cells
By: David Botton

Cell Membrane Proteins


Cell Membrane Proteins

general

not needed where simple diffusion possible (e.g. O2)

types of passive cross membrane activity

simple diffusion

diffusion through membrane

osmosis

water passing through a thin protein channel

facilitated difusion

large protein channel allows diffusion

types of active cross membrane activity

active transport

uses ATP via ATP Hydrolosis

energy sources

ATP

created through oxidative phosphorylation

oxidation-reduction reactions

in mitochondria

process

food

glycolysis, etc

krebs cycle

product of above 2 substrates

oxidative phosphorylation

ADP -> ATP

membrane pumps

use energy to move substances against the concentration gradient

move things in a low concentration to a high concentration

enzymatic activity that consumes energy (ATP)

primary active transport

can cause secondary active transport

example - leaking back in of same ion pumped out

most ATP in body is used as supply for pumps

most pumps move cations (positive ions, like NA+ K+ CA++)

types

ATP driven transport - ATPase pump

ATP -> via ATPase release phosphor -> ADP

subtypes

F0F1

made of 8 subunits

in mitochondria

used for moving H+

V0V1

made of 8 subunits

in lysosomes

used for moving H+

P-Type

subtypes

NA+K+  ATPase

exchanges NA for K

muscle and nerve cells

H+K+  ATPase

exchanges H for K

stomach and kidney membranes

SERCA CA++ ATPase

SERCA = smooth endoplasmic reticulum CA Pump

in sarcoplasmic reticulum (muscle cells)

actively remove calcium from cell

ABC-Transporters

as a family most diverse

subtypes

MDR

transports chemotherapy drugs in to cell

CFTR

found in respiratory and pancreatic cells

Cystic-fibrosis transporter

transports chloride

MDR2

in liver cell

bile secretion

membrane channels

integral membrane proteins

contain pores

sometimes open, some times closed

some cooperate with pumps

participate in regulating electrical potential of cell

main channels

sodium

potasium

calcium

some can be gated

can be one sided or two

active (all open) or inactive (all closed)  state

stimulus to open can be

electrical

chemical

called ligans

channel then called receptors

photo

mechanical

memrane carriers

qualities

made of singe polypeptides

usually alpha helix shape

spiral

called a secondary structure

some beta sheet

flat squigal

called a secondary structure

if you combine 2 structures - tertiary structure

if you combine 2 tertiary structures you get a quatenary structure

these are "integral proteins" since they cross membrane

they do not change substrates in process

types

uniporter

facilitatated diffusion of one substrate

example Glucose Transporter (GLUT)

GLUT 1

most cells

in particular red blood celss

GLUT 2

liver cells

pancreas beta cells

hypothalmus

small intestine

GLUT 3

placenta

nerve cells

testies

GLUT 4

heart cells

skeleton

muscles

GLUT 5

small intestine

sperm

symporters

facilitates a primary and secondary substrate together 

SGLT1

Sodium + Glucose transporter

small intestines

NKC1

Sodium Potassium 2-Chlorides transporter

in kidney, intestines and lungs

antiporter

one substrate in one direction the other in the opposite direction

NHE1

NA+ / H+

acid base (PH) balance

kidney and intestines

Band 3

in red blood cells

HCO3- / CL-

acid base (PH) balance

(c) 2005 All Rights Reserved - David Botton