Cell Structure and Function

A & P

The key to every biological problem must finally be sought in the cell, for every living organism is, or at some time has been, a cell. E.B. Wilson, 1925

Why Study Cell Biology?

Cells are Us

Cells are Us

Cilia on a protozoan Sperm meets egg

Cells are Us

A person contains about 100 trillion cells. That’s 100,000,000,000,000 or 1 x 1014 cells.

There are about 200 different cell types in mammals (one of us).

Cells are tiny, measuring on average about 0.002 cm (20 um) across. That’s about 1250 cells, “shoulder-to-shoulder” per inch.

nerve cell

Red and white blood cells above vessel-forming cells.

Discovery of the Cell

• Englishman Robert Hooke in 1665 used an early compound microscope to look at cork

• What is cork?– Plant material – therefore has plant cells

• Called them “cells” because they reminded him of a monastery’s rooms, called cells

• Anton van Leeuwenhoek in 1674 observed pond life in a microscope

The Cell Theory

All organisms are composed of one or more cells.

Cells are the smallest living things.

All organisms living today are descendents of an ancestral cell.

Cells arise only by division of previously existing cells.

The cell theory (proposed independently in 1838 and 1839) is a cornerstone of biology.

Schleiden

Schwann

A Sense of Scale and Abundance – Bacteria on the Head of a Pin

Two Fundamentally Different Types of Cells

A prokaryotic cell

A eukaryotic cell

Us vs. Them -Eukaryotes and Prokaryotes

The Nucleus

• The nucleus (plural: nuclei) is a large membrane-enclosed structure that contains the cell’s genetic material in the form of DNA.

• The nucleus controls many of the cell’s activities.

• Eukaryotes are cells that contain nuclei.

• Prokaryotes are cells that do not contain nuclei.

An Idealized Animal Cell

Eukaryotic Cells

• Eukaryotic cell can be likened to a factory

• There are many structure in eukaryotic cells.

• These are called organelles – “little organs”

• Two major parts of cell:– Nucleus– Cytoplasm – portion of cell outside nucleus

Major Divisions of the Eukaryotic Cell

A rat liver cell (with color enhancement to show organelles)

It’s Crowded In There

An artist’s conception of the cytoplasm - the region of a cell that’s not in the nucleus or within an organelle.

A micrograph showing cytoskeleton (red), ribosomes (green), and membrane (blue)

It’s Crowded In There

Animal and Plant Cells Have More Similarities Than Differences

Cellular Anatomy

We’ll start by seeing what role these parts play in making and moving proteins.

The Nucleus Think of the nucleus as the cell’s control center.

Two meters of human DNA fits into a nucleus that’s 0.000005 meters across.

• Contains nearly all of cell’s DNA – the instructions for making proteins• Surrounded by nuclear envelope• Most cells have one nucleus• RBCs have 0• Skeletal muscle cells have many

The Nucleus• Granular material is called

chromatin – DNA bound to protein

• When cell divides, chromatin condenses to form chromosomes which pass genetic information on to new cells

• Nucleolus - Dense region of nucleus where ribosomes are assembled

Ribosomes and the Endoplasmic Reticulum

Ribosomes

• Ribosomes – sites of protein assemblage

• Follow instructions from nucleus

The Rough Endoplasmic Reticulum

Protein movement (trafficking)

Protein synthesis (about half the cell’s proteins are made here).

Protein “proofreading”

Functions:

Golgi Apparatus

• Proteins produced in ER then move into Golgi Apparatus.

• Function – modify, sort, package proteins

• Proteins then transported to elsewhere in the cell or outside the cell

The Lysosome

Cell suicide – programmed cell death

Recycling cellular components

Functions:

Digesting food or cellular invaders

(The lysosome is not found in plant cells)

Many Diseases are Caused by Lysosome Malfunction

The Mitochondrion

Think of the mitochondrion as the powerhouse of the cell.

Both plant and animal cells contain many mitochondria.

(Mitochondria is the plural of mitochondrion)

Mitochondria• Mitochondria – convert

chemical energy stored in food into compounds the cell can use

• Inner and outer membrane• Inherited from mother• Cells that need more

energy will have more mitochondria (white meat vs. dark meat)

The name is misleading. The cytoskeleton is the skeleton of the cell, but it’s also like the muscular system, able to change the shape of cells in a flash.

The Cytoskeleton

An animal cell cytoskeleton

A Cytoskeleton Gallery

A white blood cell using the cytoskeleton to “reach out” for a hapless bacterium.

The Cytoskeleton in Action

The Cytoskeleton in Action

Cilia on a protozoan Beating sperm tail at fertilization

Smoker’s cough is due to destruction of cilia linking the airways.

Cell Membrane• Forms outer boundary

of cell• Separates contents from

environment• Made mainly of lipids

and proteins• Regulates movement

into and out of the cell

Membrane Structure• Lipids consist of

phosphate heads that are hydrophilic

• Tails consist of fatty acids that are hydrophobic

• Two layers in all

• Proteins imbedded in and on membrane

• Together they are called the “Fluid Mosaic Model”

Membrane Proteins

• Channel proteins – go through membrane and allow for passage into and out of cell

• Receptor proteins – receive information from other cells (hormones)

• I.D. proteins – identify whose cells and what type of cells

• Carrier protein – transmit material that is too large into and out of cell (facilitated diffusion)

Membrane Movements

• Equilibrium – when the concentration of a solute is the same throughout the system

• Diffusion – movement of solute from high to low concentration

• Heat, size, concentration, solubility all affect rate

• Osmosis – water diffusion through a selectively permeable membrane

Cellular Movements

• Facilitated Diffusion – still diffusion (w/o energy input) but must have a carrier protein to get through

• Think of needing to have a ticket to go to a concert

Cellular Movements• Active Transport –

carrier-mediated facilitated diffusion that requires ATP

• Goes against the conc. Gradient or from lo – hi

• Because particles are going the “wrong way” energy is required in the form of ATP

Sodium – Potassium Pump

• Simultaneously carries Na+ ions out of and K+ ions into the cell

• ATP provides energy to move 3 sodium ions out and 2 potassium ions in against gradients

• Allows for normal transmission of impulses by nerve cells

Membrane Movements• Endocytosis – engulf particle

into cell; nutrient acquistion• Phagocytosis – “cell eating”;

endocytosis of large particles such as bacteria; protective mechanism

• Pinocytosis – “cell drinking” gulping droplets of extracellular fluid; routine absorption

• Exocytosis – cell products and waste released from cell

Variations of Cells

Largest Cell Longest Cell

Cell Size Limitations

• Diffusion limits cell size– Slow and inefficient over large areas

• DNA limits cell size– Limit to how quickly DNA can be read– Limit to # of proteins built/period of time

• Surface area to volume ratio limits cell size– Volume increases faster than surface area– Requires more nutrients, produces more waste, but

with relatively smaller surface area

Question

• Which one of these has the best ratio of surface area to cell volume?

Cell Reproduction• All cells in the world

today came from preexisting cells (Cell Theory)

• How does this happen?

• The cell cycle

Cell Life Cycle• The The cell life cycle cell life cycle is the is the

series of changes a cell goes series of changes a cell goes through from the time it through from the time it forms until it divides.forms until it divides.

• Two major periods:Two major periods:– Interphase Interphase – cell grows – cell grows

and carries on metabolic and carries on metabolic activitiesactivities

– Cell Division Cell Division – cell – cell reproduces itselfreproduces itself

• Interphase – G1: Growth…– S: Copy the DNA...– G2: Growth…

• Mitosis – Process which forms two

daughter cells.

The Cell Cycle

• Longest phase in cell cycle (90+% of time)

• Cell is very active

Plant Cell Animal Cell

Interphase

Chromosomes form

MitosisStep 1: Prophase

• DNA when it is tightly packed. Chromosomes appear just before a cell reproduces.

– Formed from condensed chromatin

Chromosomes

• Two halves called sister chromatids

• Center region called centromere

• Nucleus disappears

• Centrioles migrate to opposite poles

• Spindle fibers made of microtubules form between centrioles

Prophase

Chromosomes line up

• Chromosomes attached to spindle fibers at centromeres• Pulled to middle (equator) by spindle fibers• Each sister chromatid has own fiber

Metaphase

Chromosomes begin to pull apart

Chromosomes at opposite ends

• Nucleus reforms• Chromosomes unwind

into Chromatin• Spindle breaks down• Nucleolus reappears

Telophase

Cell splits into two cells.

• Proteins called Cyclins interact with enzymes to become activated

• These proteins control the cell cycle

Control of the Cell Cycle

• Cancer – malignant growth resulting from uncontrolled cell division.

• Change in one or more genes that produce Cyclin

• Cancerous cells form masses of called tumors

• 2nd leading cause of death in US

• Affects any tissue in body

Cancer: Uncontrolled Cell Growth

– Environmental Conditions (carcinogens)• Affect Genes: segment of DNA responsible for production of a protein

• Failure to produce enzymes

• Overproduction of enzymes

– Viral Infection

Causes of Cancer

Some of the many cancers caused by smoking

1. Lung Cancer2. Head and Neck Cancer 3. Mouth Cancer4. Esophageal Cancer and Throat Cancer5. Pancreatic Cancer 6. Colorectal Cancer 7. Stomach Cancer 8. Bladder Cancer 9. Cervical Cancer 10. Breast Cancer11. Colorectal Cancer 12. Kidney Cancer 13. Myeloid Leukemia14. Liver cancer

Encyclopedia of Cancer by R.N. Tamara L. Brownhttp://www.ash.org.uk/html/factsheets/html/fact04.html

Some cancers associated with smoking

Chemicals included in cigarettes

• Diets low in fat and high in fiber content• Vitamins and minerals may also prevent cancer• Daily exercise and controlling environmental

conditions help as well.

• DON’T SMOKE!

Cancer Prevention