Eukaryotic Cell Structure

Chapter 7.3

Cellular boundaries

• Plasma Membrane/Cell Membrane

– Fxn-acts as a selectively permeable membrane

The Cell Wall • Cell Wall-def-pg.179-a fairly rigid structure

located outside the plasma membrane that provides additional support and protection-ONLY IN PLANT CELLS, FUNGI, BACTERIA!!!!

• Fxn: Cell wall forms an inflexible barrier that protects the cell & gives it support

• Composed of cellulose, which forms a thick, tough mesh of fibers & is porous to allow molecules to enter the cell

The Nucleus and Cell Control

• Nucleus Fxns:– Nucleus of cell contains the directions to make

proteins the leader of eukaryotic cells– Nucleus controls all the activities of the organelles

• Chromatin-def-pg.180- the master set of directions for making proteins-which are strands of DNA (genetic material)

– when the cell divides chromatin condenses forms chromosomes

• Nucleolus– A prominent organelle within the nucleus– Fxn: makes ribosomes

The Nucleus and Cell Control

• Ribosomes– Ribosomes-def-pg.181-are the sites

where the cell produces proteins according to the directions of DNA

– Fxn: synthesis of proteins– Can be found free floating in cytoplasm &

make proteins that perform tasks w/in the cytoplasm

– Ribosomes have a simple structure, composed of:

• RNA• Protein• Not bound by membranes

The Nucleus and Cell Control

– How ribosomes make proteins?(1) The DNA (the blueprints) within the

ribosomes must be translated into RNA then transported to the cytoplasm

(2)The RNA and the ribosomes are then transported via the nuclear pores through the nuclear envelope into the cytoplasm

•Nuclear envelope-def-pg.181- the structure that separates the nucleus from the cytoplasm, made of a double membrane of 2 phospholipid bilayer containing small nuclear pores for substances to pass through

•Cytoplasm-def-pg181-the clear, gelatinous fluid inside a cell, in which the cell’s organelles are suspended

»Once the RNA and the ribosomes are in the cytoplasm the proteins can be produced.

Assembly, Transport, and Storage

i) Organelles for assembly and transport of proteins

– Endoplasmic reticulum-def-pg.181- the site of cellular chemical reactions, and it is arranged in a series of highly folded membranes in the cytoplasm

– Fxn: the site of cellular chemical reactions

Assembly, Transport, and Storage

– Rough ER-def-pg181- ribosomes in the cytoplasm which are attached to the surface of the endoplasmic reticulum (ER).•Fxn: protein synthesis & modifies proteins

• Each protein made in the rough ER has a particular function

– Ex/ »protein that forms part of the cell

membrane»a protein released from the cell »protein transported to another organelle

Assembly, Transport, and Storage

• Organelles for assembly and transport of proteins– Smooth ER-def-pg182-areas of the ER that

are not studded with ribosomes• Fxn: Involved in numerous biochemical rxns (i.e.

production and storage of lipids)

– Golgi Apparatus-def-pg.182-a flattened stack of tubular membranes that modifies the proteins.

• Fxn: sorts proteins into packages and packs them into membrane bound structures call vesicles (like a post office)

Assembly, Transport, and Storage

Rough and Smooth Endoplasmic Reticulum

Assembly, Transport, and Storage

GolgiBodies/Apparatus

Vacuoles and storage

• Vacuoles-def-pg183-membrane bound compartments, which are larger than vesicles used for temporary storage of materials:

– Sacs used to store:– Food– Enzymes– other materials needed by a cell– waste products

– Animal cells usually don’t contain vacuoles

Vacuoles and storage

– Plant vacuoles usually contain:• Water• Sugar• Salts• Water-soluble pigments• Toxic molecules•Central Vacuole-def- found only in plant

cells, large central vacuoles are filled with sap which gives the cell added support

Lysosomes and recycling

• Lysosomes-def-pg183-organelles that contain digestive enzymes

– Fxn: digest excess or worn out organelles, food particles, and engulfed viruses or bacteria

• Lysosome Membrane fxn:– Membrane prevents the digestive enzyme inside

the lysosomes from destroying the cell

• How lysosomes work?» Lysosomes fuse with vacuoles & dispense their

enzyme into the vacuoles digesting its contents» Ex/Amoeba

Energy Transformers

• Cell organelles require great of energy for:– Protein production & modifications, – Protein transportation & digestion

• 2 organelles that provide energy:– Chloroplasts (in plants)– Mitochondria (in animals)

Chloroplasts and energy

• Chloroplast-def-pg.184-organelles that capture light energy and convert it to chemical energy

– Fxn-organelle where photosynthesis is done in a plant cell

– Chloroplasts have double membranes– Thylakoid membranes trap the energy from sunlight

& are arranged in stacks of membranous sacs called grana and surrounded by fluid called stroma

– Plastid-def-pg.184-grp of plant organelles used for storage (i.e. starches/lipids) or may contain pigments

– Chlorophyll-def-pg.184-traps light energy and gives leaves and stems their green color

Mitochondria and energy

• Chemical energy generated by chloroplasts is stored in the sugar molecules until it is broken down by the mitochondria

• Mitochondria-def-pg185- are membrane-bound organelles in plant & animal cells that transform energy for the cell.

• Fxn of mitochondria-energy that the cell doesn’t use is put into easily accessible bonds so it can be used when energy is needed.

• Structure of Mitochondria- has an outer membrane & a highly folded inner membrane– Inner membrane provides lrg surface area that can fit into

a sm space & energy-storing molecules are produced there

– Mitochondria occur in varying numbers depending on the cell function

Organelles for Support

• Cytoskeleton-def-pg.185-support structure within the cytoplasm

• The Cytoskeleton– Cytoskeleton can be dismantled &

reassembled= cell’s shape changes– Composed of a network of:

• Microtubules-def-pg185- thin, hollow cylinder made of proteins

• Microfilaments-def-pg185-smaller, solid protein fibers

• Fxn-– Maintain shape of cell– Anchor & support many organelles– Provide a highway system through which

materials move within the cell

Organelles for Cell Division

• Centrioles– Found in animal and protist cells – Occur in pairs – Made up of microtubules– Fxn-play an important role in cell

division

Organelles for Locomotion

• Cilia and flagella– Cells can have cilia or flagella which

are made up of microtubules that help with locomotion (moving) & feeding

– Cilia-def-pg.187-short, numerous projections that look like hairs

– Flagella-def-pg187-longer projections that move with a whiplike motion

• Cells usually has only 1 or 2 flagella