Cell StructureUnit 3Obj. 1.1.1, 1.1.2

What is a cell?

The basic unit of life Discovered in 1665 by Robert Hooke He thought they looked like the

rooms monks lived in, so he called them “cells”

Cell History Continued

Anton van Leeuwenhoek used a hand held microscope to look at pond scum and scrapings from his teeth in 1673

He thought they look like little animals

What kinds of cells are there?Prokaryotes = no nucleus

Example: BacteriaEukaryotes = have a nucleus

Example: Animals, plants

What kinds of organisms are there?Unicellular = made of only one cellMulticellular = made of two or

more cells

Cell Theory

Contributed to by Theodor Schwann and Matthias Jakob Schleiden in 1839 and Rudolf Virchow in 1858.

Three main ideas: 1. All living things are made of cells. 2. Cells are the basic unit of structure

and function in all living things. 3. New cells come from pre-existing

cells.

What are organelles?

Organelles are specialized parts of eukaryotic cells that have specific functions within the cells

Make the cell more efficient and complex

Nucleus

Contains the genes that control the cell = DNA

Chromatin = uncoiled DNAChromosomes = coiled DNA Surrounded by nuclear envelope =

double membrane The “information center” of the cell

Nucleolus

Makes rRNA and assembles ribosomes

Not surrounded by a membrane Cells can have 1-3 Disappears when the cell divides

Plasma Membrane Provides protection Helps cell communicate Transports substances in and out of cell Keeps the cell together Made of a phospholipid bilayer (phosphate head,

lipid tail, two layers) The head is hydrophilic (loves water), the tails are

hydrophobic (fears water) Selectively permeable

Mitochondria Where the cell performs respiration makes

ATP, a molecule the cell can use as energy for work

Major site of metabolism the more mitochondria per cell you have, the higher your metabolism will be

Folded inner membrane (cristae) more surface area for chemical reactions

Rough endoplasmic reticulumRough ER Called “rough” because it is studded

with ribosomes Makes proteins The “highway” of the cell

transports proteins

Smooth endoplasmic reticulumSmooth ER Lacks ribosomes Makes lipids Also the “highway” of the cell an

interconnected network of tubules and vesicles

Ribosomes

Protein synthesis = making proteins using RNA from the nucleus to assemble amino acids into proteins

Can be floating in cytoplasm or attached to a membrane

Lysosomes

Contain digestive enzymes Digest food, worn out organelles,

viruses, etc. Can also act as a “self-destruct

button” and cause the cell to lyse itself apoptosis

The “janitor,” “hit man,” and “suicide bomber” of the cell

Golgi Apparatus

Processes and packages macromolecules that are synthesized by the cell in vesicles (membrane bound packages)

Secretion Found in eukaryotes only

Cytoskeleton

Made of protein – microtubules and microfilaments

“Framework” of cell Provides structural support

Cytoplasm

Jelly-like substance that helps fill up the cell and suspend organelles

Site of many metabolic reactions

Plasmid

DNA molecule that is separate from and can replicate independently from chromosomal DNA

Usually found in prokaryotes

Flagellum

Tail-like projection from cell Helps cell move by whipping around

in a circle similar to helicopter blade

Cilia

Small, hair-like projections Used to help cell move and sense

environment

Pseudopodia

“False foot” Temporary projections of eukaryotic

cells Usually found in amoeba Cells use extension and contraction

to move around

Eyespots

Photoreceptive organelle = can sense light

Usually found in unicellular photosynthetic cells, like green algae

Allows the organism to respond to light and swim towards it or away from it

Centriole

Only found in animal cells Made of microtubules Help the cell divide

Cell Wall

Only found in plant cells Shapes and supports the cell Provides additional protection Made of cellulose = humans cannot

digest

Chloroplast

Found only in plant cells Contains chlorophyll = pigment

that gives plants their green color Traps sunlight to make glucose

(food) Site of photosynthesis

Vacuole

Stores water, sugar, salts, nutrients, wastes, etc.

Large and central in plant cells Small or not present in animal cells

Plant cells vs. Animal cells

Plant Cells Animal CellsMembrane surrounding cytoplasm

Yes Yes

Nucleus Yes, near cell wall

Yes, near center of cell

Mitochondria Yes YesChloroplast Yes NoVacuole Yes, large and

centralSmall or absent

Cell Wall Yes NoCentrioles No YesFood storage Starch Glycogen

To be or not to be… multicellular What are some advantages?

Differentiation each cell performs a specific task, allowing the organism to be more efficient

More control over internal conditions Greater motility able to move around and

avoid predators and find more food Genetic diversity greater chance for positive

traits What are some disadvantages?

Harder to reproduce must find a mate first Need more resources

Some different cells in our bodies

Cell Differentiation Different cells have specific jobs and

functions Can only happen in multicellular organismsStructure determines function For example:

In humans, muscle cells are extra long and narrow with multiple nuclei.

However, the doughnut-shaped red blood cells lose their nuclei early in their development and contain hemoglobin, which binds to oxygen.

How do cells differentiate? Start out as stem cells =

unspecialized, “blank slate,” can become any cell in the body

Development is usually triggered by hormones cells start to specialize

Cell communication

Cells use multiple methods to communicate Electrical or chemical signals

Recall: The cell membrane is made of a phospholipid bilayer with hydrophobic and hydrophilic parts.

It is called the fluid mosaic model fluid = hydrophobic inner layer slides around, mosaic = made of different parts, such as proteins and lipids

Studded with transport proteins and receptors so things can pass through

Why is it important for cells to communicate? Cells can sense changes in

environment Processes can be activated or

deactivated Cells can communicate with other

cells

Electrical Signals Cells are very, very close together Gap junctions = pores in cell membranes that

touch another pore in an adjacent cell membrane Nerve cells (neurons)= cells that are

specialized to send signals through the body in one direction only

Messages can be voluntary or involuntary 2 main parts of a neuron = axon and dendrite

Chemical Signals Can be very long distance hormones are special

proteins that get released into the bloodstream and travel around the whole body Must be VERY specific to make sure that the right cell

receives the message Receptor = part of cell that receives the message Can be very short distance or moderate distance