Introduction to Cell Biology

Structure and FunctionCraig Simpson

Resources

Molecular Biology of the Cell, 4th edition

Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.

New York: Garland Science; 2002.ISBN-10: 0-8153-3218-1ISBN-10: 0-8153-4072-9

Open Source at: http://www.ncbi.nlm.nih.gov/books/NBK21054/

A human body consists of:

1. Watera. 75% of total mass

2. Organsa. Brain, bones, muscles,

lungs, liver, etc3. Small Molecules

a. DNA, RNA, Proteins, sugars, fats, etc

Organs contain specialized cell types

All species originate from a single cell

• Embryonic Stem Cell– Fusion of sperm and ovum

• Human body estimated 1013 cells• Each cell has a specified function• From 1 to 1013…– Cells divide and differentiate

Figure 1-1

Cellular Differentiation

• Defn: when a less specialized cells divides into cells of more defined cellular species

• Best example: Hematopoiesis

Take home message

• Human body is complex – made up of multiple organ systems

• Organs are specialized collections of cells that have a set physiological role in the body

• All this complexity came from 1 cell– All cells contain the same genetic information…

What is a cell?

Plasma Membrane Function

• Gives cell its structure• Segregates the extracellular environment from

the cytosol (inside cell)• Gives structure to organelles• Contains molecules (lipids and proteins)

important for cellular signaling

Plasma Membrane Structure

• Lipid bilayer– Consists of phospholipids, cholesterol and

glycolipids– Hydrophilic and hydrophobic regions

• Membrane bound proteins

Phospholipids are amphiphylic

Figure 10-2

Four types of phospholipids in plasma membrane

Figure 10-12

Amphiphylic nature of phospholipids allow for formation of lipid bilayer

Figure 10-4

Cholesterol helps maintain bilayer structure

• In Eukaryotes 1 molecule cholesterol for every 4 phospholipids

• Makes bilayer more rigid• Decreases permeability of bilayer to small

water-soluble molecules• Prevents hydrocarbon chains from closely

packing and forming a solid

Cholesterol orientation amongst phospholipids

Figure 10-11

Glycolipids

• Modified through addition of sugar groups to the phosphate groups of the phospholipid

• Found exclusively on the extracellular side of the cell

• Important for interaction of the cell with its environment

Glycolipid Structure

Figure 10-16

Membrane Proteins

• 50% of mass of plasma membrane• Multiple types of interactions with lipid bilayer• Highly glycosylated• Work horse of the plasma membrane– Transport of molecules across membrane– Transport of signals from extracellular

environment/other cells (receptors)– Enzymatic reactions– Energy production

Membrane Protein IntegrationTransmembrane

a-Helix b-barrel

Figure 10-17

The Cell

Figure 12-1

Figure 12-2

Cytoplasm

• Contains:– Cytosol (aqueous environment)– All organelles

• Half the volume of the cell• Location of large amount of bioorganic

reactions– Protein synthesis and degradation– Intermediary metabolism (building and breakdown

of small molecules)

Nucleus

• Contains the Chromosome (genomic DNA)• Site of DNA replication• Site of RNA transcription

Nucleus Structure

• Two concentric membranes– Nuclear pores

• Inner membrane contains proteins that give structure to nucleus and support for chromatin

• Outer membrane is connected to the ER

Figure 12-9

Nuclear Pores

• Allow for transport of proteins into the nucleus and RNA out of the nucleus

• Multi protein complexes, highly regulated

Figure 12-10

Ribosomes• Protein synthesizing

machines– Add 2 amino acids to peptide

sequence each second• Consist of 2 subunits (50

different proteins)– 2/3 RNA, 1/3 protein

• Located in cytosol, on ER– Ie protein synthesis happens

in both ER and cytosol– Functionally and structurally

identical

Figure 6-62

Endoplasmic Reticulum (ER)

• Extends throughout the cell• Complex structure of continuous tube and

flatten sacs– Double membrane surrounding the ER lumen

(aqueous environment)• Two types– Rough ER (contains ribosomes)– Smooth ER

Endoplasmic Reticulum

Figure 12-36

Rough ER

• Protein and lipid biosynthesis– Site of protein glycosylation

• Contain ribosomes• Membrane is the site of production for all

transmembrane proteins, and lipids for the plasma membrane and other organelles

• Also produces all proteins used in intermembrane spaces (lumens of different organelles)

Smooth ER

• Don’t contain ribosomes• Exit site of synthesized proteins being

exported to the Golgi apparatus• Important in lipid synthesis• Important in steroid synthesis from

choloesterol

Golgi Apparatus

• Consists of stacks of membrane bound cisternae

• Pancake like shape

Figure 13-22

Function of Golgi

• Further modification of proteins and lipids– N and O glycosylation (important for function)

• Transport of finished proteins and lipids to plasma membrane, lysosomes and secretory vesicles (ie out of the cell)

Lysosomes and Peroxisomes

• Membrane bound vesicles• Contain enzymes• Some have lower pH• Lysosomes aid in the breakdown of proteins• Peroxisomes aid in the oxidation of small

molecules

Mitochondria

• Two highly specialized membranes that create two compartments– Internal matrix– Intermembrane space

• Inner membrane forms cristae

Figure 14-8

Mitochondria produce ATP

• The source of all energy for the cell

• Site of the citric acid cycle where glucose is broken down to NADH and ATP

• NADH is converted to ATP through the electron transport chain

Figure 14-10

Summary

• Nucleus contains information to make proteins

• Ribosome read information from nucleus to make protein

• ER and Golgi sites of protein synthesis and modification

• Mitochondria supply all the engery