Chapter 3

SIMILARITIES AND DIFFERENCES BETWEEN

CELLS

Life Must Be Dynamic

Selectivity

• We are a community of living creatures (cells) in a “pond of water”– Specialized members of the community– Outlaw cells (cancer)– Invaders

The Cell, The Smallest Living Unit

Specialization in the Society

Blood Stream

Each group of cells have unique barriers (capillaries) for exchange with the blood which allows them to create a special environment for that group of cells

Different Cell Types

• Common Processes: Processes all cells must do.

• Qualitative Differences: Unique processes that all types of cells do not do

• Quantitative differences: Some cells do more or less of some processes

Energy

• The production of high potential energy molecules such as ATP

• All cells need to do this

Cell Types Differ in their use of Energy

Glucose + 2 ADP + 2 Pi + 2 NAD+ ---> 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

Small amount of energy (ATP)

Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 3 H2O ---> 3 NADH + FADH2 + CoA-SH + GTP + 3 CO2

Large amount of energy

Without Oxygen

With OxygenUse of Fat and pyruvate

Use of Sugar

Variation in energy

Extremes in energy use

Skeletal muscle

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Brain

Reproduction (Stem Cells)

• Skin and lining of digestive system (replacement)

• Liver and muscle (damage)• Immune system (replacement

and attack)• Nervous system ???

Cell Division (proliferation)

• A complex process involving many reactions (proteins)

• Signals for and against– Inhibition– Stimulation

Copy DNA (check for mistakes: repair or apoptosis)

Mutations: mistakes that escape

Separate into two cells

Protein Synthesis and Degradation

• Both Carried out by proteins

• Synthesis depends on mRNA

• Degradation depends on proteins

• Highly controlled and selective

Turnover

The Cell Membrane

• Charge barrier

• Molecular ports (channels)

• Information ports (receptors)

• They often work together

The cell

Channels

Ion channel

Glucose channel

Relationships between Cells

• Communications: a language of chemical messages

• Coordinates functions involving many cells

• Signals and Receptors: A cell can’t respond to a signal that it can’t see

Signals

• Chemical messages made by one cell that gives directions to another cell or cells

• Two types: water soluble and fat soluble– Insulin – Glucocorticoids

Frequency and intensity modulated signals

Every hormone is a different “voice” talking to

those cells in the community that can listen

Receptors

• A cell can only respond to the “voices” that it can hear

• Receptors mediate many things– Open channels through the membrane– Alter gene expression– Signals often cascade and feedback

Receptors

Receptors

• Respond to the signal

• Adjust and remember

• Tolerance

• Dependence

Other Forms of Life in the Community

• Viruses

• Bacteria

• Fungi

• Parasites