Overview of Cells

• Prokaryotes vs Eukaryotes

• The Cell Organelles

• The Endosymbiotic Theory

• Archaea

• Bacteria

Prokaryotic Cells

• Come in many different shapes and sizes

.5 µm – 2 µm, up to 60 µm long

• Have large surface to volume ration – nutrients from outside can easily

reach all parts of the cell

• Protists

• Fungi

• Animal Cells

• Plant Cells

Eukaryotic Cells

• Like prokaryotic cells, eukaryotic cells come in many different shapes and sizes, but have the same basic set of organelles

• Multicellular organisms (fungi, plants and animals) have specialized eukaryotic cells that each perform a particular job and all work together for the benefit of the organism

Eukaryotic CellsCommon Organelles

– Plasma membrane

– Nucleus Chromatin (DNA) Nucleolus Nuclear Envelope

– Ribosomes

– Rough Endoplasmic Reticulum (rough ER)

– Smooth Endoplasmic Reticulum (smooth ER)

– Golgi Apparatus

– Centrioles

– Mitochondria

– Cytoskeleton

– Vesicles, Peroxisomes, Lysosomes, Small Vacuoles

Eukaryotic CellsOrganelles only found in Plants

– All those in animal cells except Centrioles

– plus

Cell Wall

Chloroplasts

Large Vacuoles

– The cell wall and vacuoles help plant cells maintain a rigidshape (keep plant fromdrooping)

Organelles• Organelles are the parts within a cell that have specific functions

• Prokaryotic cells (e.g. bacteria) are smaller and less complex (fewer organelles) than eukaryotic cells.

Prokaryotic Cells

– Plasma Membrane

– Cytoplasm

– Cell Wall

– DNA (no nucleus)

– Ribosomes

Eukaryotic Cells

– Plasma Membrane

– Cytoplasm– Nucleus

Chromatin (DNA) Nucleolus Nuclear Envelope

– Ribosomes– Vesicles, Peroxisomes, Lysosomes– Rough Endoplasmic Reticulum– Smooth Endoplasmic Reticulum– Golgi Apparatus– Centrioles– Mitochondria– Cytoskeleton

Plant Cells (eukaryotic)

– Cell Wall

– Chloroplasts

– Vacuole

Polysaccharides

Organelles are made of:

• Proteins – made of amino acids

• Lipids – made of fatty acids

• Carbohydrates - polysaccharides made of sacharides (sugars)

• Nucleic Acids (DNA and RNA) – made of nucleotides

Nucleic Acids

LipidsProteins (Polypeptides)

Organelles

Components found in all cells

• Made of a Phospholipid Bilayer

• Various proteins, lipids, and sugars float in membrane

• Semipermeable

Small hydrophobic molecules pass easily through

Contains pores that enable water and very small ions to pass through

large molecules must pass through channel proteins

Plasma Membrane

Eukaryotic cells also membrane-bound internal organelles composed of lipid bilayer membranes

• Nuclear Envelope

• Golgi Apparatus

• Endoplasmic Reticulum (rough and smooth)

• Mitochondria

• Chloroplasts (in plants)

• Vesicles, Lysosomes, Peroxisomes & Vacuoles

Components found in all cells

Plasma Membrane

• The fluid that fills cells and surrounds the organelles

• Consists of:

• Water (mostly)

• Proteins (e.g. hormones and enzymes)

• Small Molecules (e.g. ions)

Components found in all cells

Cytoplasm

• Prokaryotic Cells

• May be linear or circular

• Contained in the nuclear region (nucleoid)

• May also include short, circular plasmids

• Eukaryotic Cells

• Longer (approx. 9 feet per cell in humans), coiled around histone proteins to help pack it into the cell

• Always linear

• Contained in the nucleus

• Known as chromatin when relaxed and chromosomes when condensed (supercoiled)

Components found in all cells

DNA

• Float freely in the cytoplasm of prokaryotic and eukaryotic cells

• Also coat the rough ER of eukaryotic cells

Components found in all cells

Ribosomes

Components found in all cells

Ribosomes• Build proteins using instructions encoded in DNA

• Build proteins using instructions encoded in DNA

• Complex of protein and rRNA forming two subunits

Purple = Proteins

Blue = rRNA of small subunit

Grey = rRNA of large subunit

Components found in all cells

Ribosomes

• Nuclear Envelope

double membrane

nuclear pores allow RNA to exit

• Chromatin – “relaxed” DNA

• Nucleolus – where ribosomes are assembled

Nucleus

Components found only in Eukaryotic Cells

• Folded membrane that forms compartments where newly synthesized proteins are processed (cut, joined, folded into their final shape)

• Ribosomes bind to rough ER when they start to synthesize proteins that are intended to be exported from the cell – the proteins enter the ER directly from the ribosome

Components found only in Eukaryotic Cells

Rough Endoplasmic Reticulum (ER)

• Synthesis of lipids and steroids

• Metabolism of carbohydrates and steroids

• Regulation of calcium concentration

• Drug/toxin detoxification

• Attachment of receptors on cell membrane

Components found only in Eukaryotic Cells

Smooth Endoplasmic Reticulum (ER)

• Folded membranes form compartments that each contain different enzymes which selectively modify the contents depending on where they are destined to end up

• Processes and packages macromolecules produced by the cell (e.g. proteins and lipids) – sent out as excretory vesicles “labeled” for their destination

Components found only in Eukaryotic Cells

Golgi Apparatus

• Network of long protein fibers (microtubules, actin filaments, and intermediate filaments)

• Helps support cell shape and movement

• transport organelles and vesicles throughout the cytoplasm to other areas within the cell

The cytoskeleton is stained green in this image (the nucleus is stained blue and the cell membrane is stained red)

Components found only in Eukaryotic Cells

Cytoskeleton

Store nutrients such as starch, glycogen, or fat

Take up most of space in many plant cells, full of water

Components found only in Eukaryotic Cells

Vacuoles

Peroxisomes

Lysosomes

Membranous Sacs

In animal cells – full of enzymes that oxidize amino acids

In plant cells – full of enzymes that oxidize fat

In plant and animal cells – convert hydrogen peroxide to water

Contain digestive enzymes

Fuse with vesicles and vacuoles containing food, cell refuse, captured bacteria, etc

Carry products of protein synthesis to parts of the cell or to membrane to be excreted via exocytosis

Excretory Vesicles

• Form centrosome and initiate formation of the mitotic spindle during cellular replication

• Found in animal cells and some plant cells – not in higher plants or fungi

• Composed of microtubules (like those in the cytoskeleton)

Components found only in Eukaryotic Cells

Centrioles

• Brakes down glucose (sugar) using oxygen to produce energy for the cell = cellular respiration

• Many cells have only a single mitochondrion, whereas others can contain several thousand

• Have own DNA and ribosomes

Components found only in Eukaryotic Cells

Mitochondrion (plural – Mitochondria)

• Use light energy to convert atoms in water and CO2 (from air) into sugars and starches

• Have double membrane (inner and outer)

• Have own DNA and ribosomes

• Grana (stacks of thylakoids) – where light energy is captured by chlorophyll and converted into chemical energy = photosynthesis

• Stroma – fluid inside chloroplasts

• Chlorophyll – light-absorbing pigment in thylakoids

Photosynthetic Organelles

Chloroplasts (plant cells and photosynthetic protists)

Endosymbiotic Theory• Concept that mitochondria and chloroplasts are the result of years of

evolution initiated by the endocytosis of bacteria and blue-green algae which, instead of becoming digested, became symbiotic

Endosymbiotic Theory• Concept that mitochondria and chloroplasts are the result of years of

evolution initiated by the endocytosis of bacteria and blue-green algae which, instead of becoming digested, became symbiotic

Have their own DNA which resembles bacterial DNA

Have their own 70s ribosomes and produce their own proteins

Double membrane indicates they entered cell via endocytosis

Membrane composition strongly resembles Gram-negative bacteria

Divide within eukaryotic cell via binary fission (the way of bacteria)

Similar symbiotic relationships exist between organisms that are still distinct species from one another

• Some evidence indicates that eukaryotic flagella and cilia may have originated as symbiotic bacteria as well

Evolution of Eukaryotes

Some protists lack mitonchondria which indicates that the eukaryote lineage evolved before the ancestral bacterial of mitochondria established a symbiotic relationship with early protists

Cell Walls• Tough, rigid wall around cell membrane

Most prokaryotes

Eukaryotes: plants, algae and fungi only

• Functions:

Prevents over-expansion when water enters the cell via osmosis

Structural support (otherwise cells would be spherical)

Protection

• Composed of cellulose and/or chitin in eukaryotes (only plant and fungi cells have cell walls in eukaryotes)

Cell Walls

• Flagella

Creates movement in prokaryotes by rotating like a propeller

Whip-like movement in eukaryotes

Larger and more complex in eukaryotes- common in protozoa, found in some algae- only spermatozoa cells in humans

Positive chemotaxis – cell moves up concentration gradient

Negative chemotaxis – cell moves down concentration gradient

Phototaxis – cell moves towards (positive) or away from (negative) light

Other External Structures

• Cilia (eukaryotes only)

Numerous on surface of cell

Beat in a coordinated pattern creating a wave of movement

Mostly occur in protozoa, but some human cells too (like those lining the respiratory tract)

• Pili (prokaryotes only)

also known as fimbria

Hair-like appendage on bacteria thathelp the bacteria connect to other cells in order to exchange plasmids (DNA)

Other External Structures