Cell Structure

Unit 3Obj. 1.1.1, 1.1.2

Place an “X” next to the things you think are made of cells

___ flowers ___ hamburger ___ leaf

___ skin ___ DNA ___ seeds ___ proteins ___ calcium ___ water ___ rocks___ apples ___ sugar ___ milk ___ sand ___ blood ___ bone ___ worms ___ saliva ___ lungs ___ bacteria ___

mushroom

What is a cell?

The smallest unit of life; the smallest thing biologists study

RECALL: Organization of Living Things:

Cell Tissue Organ Organ system Organism

What is a cell?

Cells have smaller parts inside of them called organelles

This means “little organ.” They perform special functions for the cell to keep it (and the organism) alive.

What is a cell?

Cells were discovered in 1665 by Robert Hooke

He thought they looked like the rooms monks lived in, so he called them “cells”

What is a cell?

Anton van Leeuwenhoek was the first to see living cells. He used a hand held microscope to look at pond scum and scrapings from his teeth in 1673.

He thought they look like little animals.

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 one or more

cells.▪ Unicellular = one-celled organism▪ Multicellular = organism made from many cells

2. Cells are the basic unit of structure and function in all living things.

3. All new cells come from pre-existing cells.

Types of cells

1. Prokaryotic (means “before nucleus”)

No nucleus, unbound DNA

No membrane-bound organelles

Small and simple; “older” type of cell

Examples: Bacteria

2. Eukaryotic (means “true nucleus”)

Has a nucleus, DNA is inside nucleus

Has organelles Larger and more

complex; “younger” type of cell

Examples: Plants and Animals

Cell Membrane

Aka “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 Found in all cells

Cell Wall

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

digest

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

Mitochondria

Where the cell performs respiration makes ATP, a molecule the cell can use as energy for work

Major site of metabolism Folded inner membrane (cristae)

more surface area for chemical reactions

Chloroplast

Found only in plant cells Contains chlorophyll = pigment

that gives plants their green color Traps sunlight to make glucose

(food) Site of photosynthesis

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

Vacuole

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

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

Cytoplasm

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

Site of many metabolic reactions

Centriole

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

Golgi Apparatus

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

Secretion Found in eukaryotes only

Rough endoplasmic reticulum

Rough ER Called “rough” because it is studded

with ribosomes Makes proteins The “highway” of the cell

transports proteins

Smooth endoplasmic reticulum

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

interconnected network of tubules and vesicles

Cytoskeleton

Made of protein – microtubules and microfilaments

“Framework” of cell Provides structural support

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

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

Plasmid

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

Usually found in prokaryotes

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

Plant cells vs. Animal cells

Plant Cells Animal Cells

Membrane surrounding cytoplasm

Yes Yes

Nucleus Yes, near cell wall

Yes, near center of cell

Mitochondria Yes Yes

Chloroplast Yes No

Vacuole Yes, large and central

Small or absent

Cell Wall Yes No

Centrioles No Yes

Food storage Starch Glycogen

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

Differentiation 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

Cell Specialization

When cells have different jobs or functions

Only multicellular organisms can have specialized cells

Specialized Animal Cells

Muscle, bone, brain, nerve, skin, hair= all different cells with different functions

Muscle cells: have more mitochondria than other cells= more metabolism!

Cool fact: Muscle cells have more than one nucleus!

Red Blood Cells: lose their nucleus and are donut-shaped to carry oxygen molecules

Remember: Hemoglobin is a protein

How do you get specialized cells?

Start as a stem cell = has the ability to become any cell in the body a “blank slate”

Gets signals (usually hormones) to become a certain cell type (this is called differentiation)

Cell Communication - Chemical Hormones = proteins that are used by both

plant and animal cells to send messages Produced in large amounts, usually in

response to something environmental Travel slowly throughout the organism Endocrine system (thyroid, testes, ovaries,

pituitary gland, etc.) releases hormones into the blood stream

Affects only those cells with the right receptors = has effects on certain cells in the body

Cell Communication - Electrical Neurons = cells in the

nervous system that transmit information throughout the body. Animals only!

Sends messages that can be voluntary or involuntary

Send out neurotransmitters that get passed from neuron to neuron

Neurons have two main parts: dendrite and axon