C E L L S T R U C T U R E

Biology Chapter 7

7.1 Cell Features

Typical human cell is many times smaller than grain of sand

1.) First become aware of cells in the 1600s when Robert Hooke invented microscope, formed the term “cell”

2.) 10 years later, Anton van Leeuwenhoek used a microscope to view water from a pond

He discovered many living creatures in which he named “animalcules”

Now we know them as single-celled organisms

SCIENTISTS CONTINUED…

3) Matthias Schleiden

1838 – viewed plant cells

Concluded… All PLANTS are made up of cells

4) Theordor Schwann

1839 – viewed animal cells

Concluded… All ANIMALS are made up of cells

5) Rudolph Virchow

1855 – all cells must develop from other cells

Cell Theory

Cell Theory (Schleiden, Schwann, & Virchow)

All living things are made of one or more cells

Cells are the basic units of structure and function in organisms

All cells arise from existing cells

Cell Size

Small cells function more efficiently than large cells

About 100 trillion cells in the human body

All substance that enter or leave must cross the cell’s membrane

If surface area-to-volume ratio is low, substances cannot enter and leave the cell in numbers large enough to meet the cell’s needs

Small cells can exchange things more readily because they have a HIGHER surface area-to-volume ratio

Common Features of Cells

Cell membrane – outer boundary

Regulates what enters and leaves the cells

Cytoplasm – the cell’s interior

Organelles are suspended in cytoplasm- Contains cytosol, the fluid

Cytoskeleton – microscopic fibers suspended in cytoplasm, gives shape

Ribosomes –most cells (red blood Cells don’t have)

Where proteins are made

DNA

Provides instructions for making proteins

Types of Cells: Prokaryotes

Smallest and simplest cells

Single-celled

No nucleus or internal compartments(organelles)

DNA clumps in nucleoid

Cannot carry out many specialized functions

Ex – ALL bacteria

Characteristics of Prokaryotes

Exist in broad range of conditions Grow and divide rapidly Diverse – some need oxygen, some die with oxygen, some

make their own food Cytoplasm includes everything inside the cell membrane DNA – singular, circular molecule Cell wall – provides structure and support

Made of strands of polysaccharides connected by short chains of amino acids

Fungi and plants also have cell wall

Lack internal supporting skeleton (cytoskeleton) Some surrounded by capsule

Enables them to cling to almost anything – teeth, skin, food

Flagella – long threadlike structures – enable movement

Cilia v. Flagella

Types of Cells: Eukaryotic Cells

Have a nucleus and internal compartments (organelles) Nucleus – houses the cell’s DNA

Organelle – structure that carries out specific tasks bound by a membrane

Cytoplasm – everything inside the cell, outside the nucleus

Cilia – single-celled eukaryotes Flagella or cilia help propel cells through their environment

Cytoskeleton – web of protein fibers Holds the cell together and keeps the cell membrane from collapsing

Fluid surrounding the organelles, membranes, and cytoskeleton is called cytosol.

Typical Eukaryotic Cell

Video

Slide 26, Holt PP

Comparison of Prokaryotic v Eukaryotic Cell

Cytoskeleton

Provides interior framework of animal cell Composed of intricate network of protein fibers

Support the shape of cell

Three kinds of cytoskeleton fibers Actin fibers – microfilaments

made of protein - actin Form just beneath cell surface Play major role in determining shape of cells

Microtubules made of protein tubulin Act as highway system for transportation of information from the

nucleus to different parts of the cell

Intermediate fibers Thick ropes made of protein Confine ribosomes and enzymes to particular regions of the cell

Cytoskeleton Structures

The Cell Membrane

Cytoplasm is contained by phospholipid bilayer called cell membrane

Separates cell from its surroundings

Selectively Permeable

Allows only certain substances to pass through

Not rigid like eggshell, fluid like soap bubble

Fluidity caused by lipids

Phospholipid Bilayer

Section 2-Cell Organelles Organelle- “little

organ” structure that carries out specific tasks

Found only inside eukaryotic cells

All the stuff in between the organelles is cytoplasm

THE NUCLEUS “control center”

Most functions of eukaryotic cell controlled by nucleus

Surrounded by double membrane called the nuclear membrane

Also called nuclear envelope

Made of 2 lipid bilayers that separate nucleus from cytoplasm

Nuclear pores are scattered across nucleus

Small openings that allow substances to move into the cytoplasm

Contains DNA, hereditary information in structures called chromosomes, made of chromatin

Nucleolus – creates ribosomes

The Nucleus

Ribosome–Makes Proteins

Site of protein synthesis

Found attached to rough ER or floating free in cytoplasm

Produced in a part of the nucleus called the nucleolus

That looks familiar…what is a

polypeptide?

Endoplasmic

Reticulum A.k.a. “ER”

Connected to nuclear membrane ER – extensive system of

internal membranes that move proteins and other substances through the cell

Made of lipid bilayer with embedded proteins

Rough ER: studded with ribosomes; it transports proteins from nucleus to golgi apparatus Appears “rough” because

ribosomes line the outside

Smooth ER: no ribosomes; it makes lipids uses enzymes to break down toxic substances

Smooth ER – lacks ribosomes and appears smooth when viewed

Endoplasmic Reticulum

Endoplasmic Reticulum

Golgi Apparatus

Looks like a stack of plates –made of flattened, membrane-bound sacs

“distribution center”

Modifies and packages proteins and other materials for export

Molecules transported to and from the Golgi by means of vesicles

Golgi Apparatus

Vesicles

Vesicles –used to transport material around the cell

maintain homeostasis by storing and releasing substances as cell needs

Some are released from Golgi apparatus carrying proteins

Lysosomes

Vesicles which are small, spherical and contain the cell’s digestive enzymes

Acts as “garbage disposal” of cell

Contain digestive enzymes that break down wastes

Also digest food

Mitochondria “Power House”

Takes energy from organic compounds to make ATP through cellular respiration

ATP is main energy source of cells

Some made in cytosol, most in mitochondria

Cells that have high energy needs, have many mitochondria

Has two membranes

Outer is smooth

Inner is greatly folded

Mitochondrial DNA

Nucleus not only organelle that contains nucleic acids

Mitochondria also have DNA and ribosomes

Make some of their own proteins

Mitochondrial DNA is independent (different) of nuclear DNA

Similar to circular DNA of prokaryotic cells

Supports theory that primitive prokaryotes are the ancestors of mitochondria

Always inherited from your mother

Centriole

Aids in cell division

ONLY in animal cells

Made of microtubules

Where else have we talked

about microtubules?

Structure of Plant Cells

Plant cells have 3 additional organelles not found in animal cells

Central vacuole

Chloroplast

Cell wall

Central Vacuole

Consumes large portion of cell

Membrane-bound

Stores water

may contain substances including ions, nutrients, and wastes

When full, makes the cell rigid

Enables a plant to stand upright

Vacuoles in animal cells?

Stores primarily water and occasionally solid (food) for a cell

present in all plant cells

Found in only in some animal cells.

Vacuoles are formed by the fusion of multiple membrane vesicles and are basically just larger forms of these.

Chloroplast

Found only in plant cells

Contains the green pigment chlorophyll

Site of food (glucose) production (Photosynthesis)

Bound by a double membrane

Cell Wall

Found in plant and bacterial cells

Rigid, protective barrier

Located outside of the cell membrane

Helps maintain shape

Made of cellulose (fiber)

Quick Review

Which organelle is the control center of the cell?

Nucleus

Which organelle holds the cell together?

Cell membrane

Which organelles are not found in animal cells?

Cell wall, central vacuole, chloroplasts

Which organelle helps plant cells make food?

Chloroplasts

What does E.R. stand for?

Endoplasmic reticulum

Protein Synthesis DNA sends message of what protein to make from

nucleus to the ribosome

Ribosome produces the protein

Protein crosses membrane of the ER, pinches off, and is carried in a vesicle

Vesicles that contain newly made proteins move through the cytoplasm from the ER to the Golgi apparatus

Enzymes modify the proteins that are received by the golgi apparatus

Modified proteins are enclosed inside a new vesicle that buds from surface of Golgi body

Protein transported to cell membrane to be released or elsewhere in cell to be used