Organelles

Types of Organelles

• Nonmembranous organelles: – no membrane– direct contact with cytosol (cytoplasm)

• Membranous organelles: – covered with plasma membrane– isolated from cytosol (cytoplasm)• 6 types of nonmembranous organelles: – cytoskeleton – microvilli – centrioles

-cilia – ribosomes – proteasomes

How does the nucleus control the cell?• Is the cell’s control center• Nucleus:

– largest organelle• Nuclear envelope:

– double membrane around the nucleus

• Perinuclear space:– between 2 layers of

nuclear envelope • Nuclear pores:

– communication passages

Within the Nucleus• DNA:– all information to build and run organisms

• Nucleoplasm:– fluid containing ions, enzymes, nucleotides, and

some RNA

• Nuclear matrix:– support filaments

Nucleoli in Nucleus• Are related to protein production• Are made of RNA, enzymes, and histones• Synthesize rRNA and ribosomal subunits

Ribosomes

SEM of rough ER (ribosomes attached to

membranes)

Ribosomes• Two types:

– free ribosomes in cytoplasm:• proteins for cell

– fixed ribosomes attached to ER:• proteins for secretion

• Translate the genetic code into proteins.• Build polypeptides in protein synthesis• 60% RNA and 40% protein.

Proteasomes (found in the nucleus and the cytoplasm)

• Contain enzymes (proteases)• Disassemble damaged proteins for recycling

Endoplasmic reticulum

TEM of rough ER (ribosomes attached to

membranes)

Endoplasmic Reticulum (ER)• endo = within, plasm = cytoplasm, reticulum = network

• Little net• Network of interconnected closed membrane vesicles• Single membrane• Divides cell into compartments• Place of protein and phospholipids synthesis• Connected with the nuclear envelope• Cisternae are storage chambers within membranes

Functions of ER

• Synthesis of proteins, carbohydrates, and lipids• Storage of synthesized molecules and materials• Transport of materials within the ER• Detoxification of drugs or toxins

• It is of 2 types:1. Rough ER2. Smooth ER

Rough Endoplasmic Reticulum• Network of continuous sacs,

studded with ribosomes.• Manufactures, pro-cesses, and

transports proteins for export from cell.

• Continuous with nuclear envelope.

• Surface covered with ribosomes:– active in protein and

glycoprotein synthesis (late r inserted in the cell membrane and secreted from the cell)

– folds polypeptides protein structures

– encloses products in transport vesicles

Smooth Endoplasmic Reticulum

• Similar in appearance to rough ER, but without the ribosomes.

• Involved in the production of lipids, carbohydrate metabolism, and detoxification of drugs and poisons.

• Ca (2+) storage• Synthesizes lipids and carbohydrates:– phospholipids and cholesterol (membranes)– steroid hormones (reproductive system)– glycerides (storage in liver and fat cells)– glycogen (storage in muscles)

Golgi complex

TEM of Golgi complex

ER and Golgi complex

The ER and Golgi complex work together to secrete substances from the cell (via exocytosis)

Golgi Bodies

– Contains several hundred flattened compartments and vesicles

– Secretory vesicles:• modify and package products for exocytosis

– Membrane renewal vesicles:• add or remove membrane components

– Transport vesicles:• Carry materials to and from Golgi apparatus

Golgi Bodies

Lysosomes

SEM of two lysosomes containing undigested

materialCell death caused by lysosomes

removes webbing

Lysosome Functions• Powerful enzyme-containing vesicles:

– lyso = dissolve, soma = body• Clean up inside cells:

– break down large molecules– attack bacteria– recycle damaged organelles– ejects wastes by exocytosis

• Primary lysosome: – formed by Golgi and inactive enzymes

• Secondary lysosome: – lysosome fused with damaged organelle– digestive enzymes activated– toxic chemicals isolated

ChloroplastsTEM of

chloroplasts

• Photosynthetic plant cells also contain chloroplasts (a plastid) that capture energy from sunlight.

• They produce and store carbohydrates like miniature gardens and warehouses.

• LOCATIONinside photosynthetic cells only, suspended in the cytosol

• DESCRIPTION green, disk shaped contains chlorophyll and the enzymes required for photosynthesis

FUNCTION• absorb sunlight energy • photosynthesis occurs here: glucose is synthesized from Carbon Dioxide and

water

Chloroplasts

Chloroplast

PRESENT IN:• PROKARYOTIC CELLS? NO• PLANT CELLS? YES• ANIMAL CELLS?

NO

VISIBLE WITH:• LIGHT MICROCOPE?

YES

• ELECTRON MICROSCOPE?YES

Mitochondria

TEM SEM

Notice the many folds

MitochondriaTubular susage shapedDouble membraneOwn DNA and ribosomesHave smooth outer membrane and folded inner membrane

(cristae)Matrix:

– fluid around cristae

Mitochondrial Function• Mitochondrion takes chemical energy from food

(glucose):– produces energy molecule ATP

Figure 3–9b

Animal and plant cells

Animal cell Plant cell

Cell skeleton

Three structures that make up the cytoskeleton of a cell

The Cytoskeleton(Structural proteins for shape and strength)

• Microfilaments• Solid rods of globular proteins.• Important component of cytoskeleton which

offers support to cell structure.Thin filaments composed of the protein actin:

• provide additional mechanical strength • durable (collagen)• strengthen cell and maintain shape• stabilize organelles• stabilize cell position

• Microtubules – Large, hollow tubes of

tubulin protein:• attach to centrosome• strengthen cell and

anchor organelles• change cell shape• form spindle

apparatus

• Microvilli• Increase surface area for

absorption• Attach to cytoskeleton