Cells

The Signal Hypothesis

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Rough Endoplasmic Reticulum (FUNCTION)

1. Ribosomes associated with the rough ER synthesize proteins. 2. New proteins are folded and processed in the rough ER lumen.

According to phylogeny, or evolutionary history, there are three domains:

1.Bacteria 2.Archaea 3.Eukarya - eukaryotic

Peroxisomes (FUNCTION)

1.Center of oxidation reactions 2.Specialized peroxisomes in plants called glyoxysomes are packed with enzymes that oxidize fats to form a compound that can be used to store energy for the cell.

Eukaryotes and Prokaryotes Compared (4 key differences)

1.Eukaryotic chromosomes are found inside a membrane-bound compartment called a nucleus. 2.Eukaryotic cells are often much larger. 3.Eukaryotic cells contain extensive amounts of internal membrane. 4.Eukaryotic cells feature a diverse and dynamic cytoskeleton.

The Nucleus (FUNCTION)

1.Information storage and processing -Contains the cell's chromosomes 2.Ribosomal RNA synthesis (in the nucleolus)

Lysosomes (STRUCTURE)

1.Lysosomes are single-membrane-bound structures containing approximately 40 different digestive enzymes. 2.Lysosomes are found in animal cells.

Mitochondria (STRUCTURE)

1.Mitochondria have two membranes; the inner one is folded into a series of sac-like cristae. The solution inside the cristae is called the mitochondrial matrix. 2.Mitochondria have their own DNA and manufacture their own ribosomes.

Chloroplasts (STRUCTURE)

1.Most plant and algal cells have chloroplasts that, like mitochondria, have a double membrane and contain their own DNA. 2.Chloroplasts contain membrane-bound, flattened vesicles called thylakoids, which are stacked into piles called grana. Outside the thylakoids is the solution called the stroma.

How Are Materials Delivered to Lysosomes? (three processes)

1.Phagocytosis 2.Autophagy 3.Receptor-mediated endocytosis

Bacterial cells vary greatly in size and shape, but most bacteria contain several structural similarities:

1.Plasma membrane 2.A single chromosome 3.Ribosomes, which synthesize proteins 4.Stiff cell wall

According to morphology, there are two broad groupings of life:

1.Prokaryotes, which lack a membrane-bound nucleus 2.Eukaryotes, which have such a nucleus

Ribosomes (STRUCTURE)

1.Ribosomes are non-membranous (they are not considered organelles). 2.Have large and small subunits, both containing RNA molecules and protein 3.Ribosomes can be attached to the rough ER or free in the cytosol, the fluid part of the cytoplasm.

The compartmentalization of eukaryotic cells offers two primary advantages:

1.Separation of incompatible chemical reactions 2.Increasing the efficiency of chemical reactions

Vacuoles (FUNCTION)

1.Some vacuoles are specialized for digestion. 2.Most vacuoles are used for storage of water and/or ions to help the cell maintain its normal volume.

Golgi Apparatus (FUNCTION)

1.The Golgi apparatus processes, sorts, and ships proteins synthesized in the rough ER. 2.Membranous vesicles carry materials to and from the organelle.

The Nucleus (STRUCTURE)

1.The nucleus is surrounded by a double-membrane nuclear envelope. 2.The nucleus has a distinct region called the nucleolus.

Rough Endoplasmic Reticulum (STRUCTURE)

1.The rough endoplasmic reticulum (rough ER, RER) is a network of membrane-bound tubes and sacs studded with ribosomes. -The interior is called the lumen. 2.The rough ER is continuous with the nuclear envelope.

Bacterial Organelles

1.These compartments qualify as organelles ("little organs"). 2.An organelle is a membrane-bound compartment inside the cell that contains enzymes or structures specialized for a particular function. 3.Organelles are common in eukaryotic cells. 4.Each type of bacterial organelle is found in certain species. •Bacterial organelles perform an array of tasks

Vacuoles (STRUCTURE)

1.Vacuoles are large membrane-bound structures found in plants and fungi. 2.Some contain digestive enzymes.

Smooth Endoplasmic Reticulum (FUNCTION)

2.Enzymes within the smooth ER may synthesize fatty acids and phospholipids, or break down poisonous lipids. 3.Reservoir for Ca2+ ions

Mitochondria (FUNCTION)

ATP production is a mitochondrion's core function.

Chloroplasts (FUNCTION)

Chloroplasts convert light energy to chemical energy - in other words, they perform photosynthesis.

Prokaryotic Cells (Internal Structure)

In addition to the nucleoid chromosome and plasmids, other structures are contained within the cytoplasm: 1.All prokaryotic cells contain ribosomes, consisting of RNA molecules and protein, for protein synthesis. 2.Many prokaryotes have internal photosynthetic membranes. 3.Some prokaryotes have membrane-enclosed organelles. 4.The inside of many prokaryotic cells is supported by a cytoskeleton of long, thin protein filaments.

Lysosomes (FUNCTION)

Lysosomes are used for digestion and waste processing.

Prokaryotic Cells (genetic information)

Most prokaryotic species have one supercoiled circular chromosome found in the nucleoid region of the cell. 1.The chromosome contains a long strand of DNA and a few supportive proteins. 2.In addition to the large chromosome, many bacteria contain plasmids. 3.Small, supercoiled, circular DNA molecules 4.Plasmids usually contain genes that help the cell adapt to unusual environmental conditions.

Peroxisomes (STRUCTURE)

Peroxisomes are globular organelles bound by a single membrane.

Ribosomes (FUNCTION)

Protein Synthesis

Golgi Apparatus (STRUCTURE)

The Golgi apparatus is formed by a series of stacked flat membranous sacs called cisternae.

Smooth Endoplasmic Reticulum (STRUCTURE)

The smooth endoplasmic reticulum (smooth ER, SER) lacks the ribosomes associated with the rough ER.

Cells

are highly dynamic and integrated; within a cell, thousands of chemical reactions occur every second, molecules are constantly moving across the plasma membrane, cell products are transported along protein fibers, and elements of the cell's internal skeleton grow and shrink.

Endocytosis

is a process by which the cell membrane can pinch off a vesicle to bring outside material into the cell. -In addition to phagocytosis and receptor-mediated endocytosis, a third type of endocytosis called pinocytosis brings fluid into the cell.

Cells Cytoskeleton

provides a structural framework within the cell, and plays a role in cell division, movement, and transport.

Prokaryotic Cells (structural overview)

•All prokaryotes lack a membrane-bound nucleus. •Recent advances in microscopy reveal complexity in prokaryotic structure.

Eukaryotes

•Eukaryotes range from microscopic algae to 100-meter-tall redwood trees. •Many eukaryotes are multicellular, others are unicellular. •Most eukaryotic cells are larger than most prokaryotic cells. •The relatively large size of the eukaryotic cell makes it difficult for molecules to diffuse across the entire cell. (This problem is partially solved by breaking up the large cell volume into several smaller membrane-bound organelles.)

The Cell Wall

•Fungi, algae, and plants have a stiff outer cell wall that protects the cell. 1.In plants and algae, the cell wall's primary component is cellulose. 2.In fungi, the primary component is chitin. • Some plants have a secondary cell wall containing lignin.

How Are Molecules Imported into the Nucleus?

•Messenger RNAs and ribosomes are synthesized in the nucleus and exported to the cytoplasm. Materials such as proteins needed in the nucleus are imported into the nucleus. •Movement of proteins and other large molecules into and out of the nucleus is an energy-demanding process. -Proteins destined for the nucleus have a molecular "zip code"—a 17-amino-acid-long nuclear localization signal (NLS)—which allows them to enter the nucleus.

Prokaryotic Cells (external structure)

•Some prokaryotes have tail-like flagella on the cell surface that spin around to move the cell. •Most prokaryotes have a cell wall. 1.Bacterial and archaeal cell walls are a tough, fibrous layer that surrounds the plasma membrane. •Many species have an additional layer outside the cell wall composed of glycolipids.

Cytoskeleton

•The cytoskeleton, composed of protein fibers, gives the cell shape and structural stability, and aids cell movement and transport of materials within the cell. •The cytoskeleton organizes all of the organelles and other cellular structures into a cohesive whole.

The Endomembrane System

•The endomembrane system is composed of the smooth and rough ER and the Golgi apparatus, and is the primary system for protein and lipid synthesis. •Ions, ATP, amino acids, and other small molecules diffuse randomly throughout the cell, but the movement of proteins and other large molecules is energy demanding and tightly regulated.

The Nuclear Envelope: A Transport Mechanism

•The nuclear envelope has two membranes, each consisting of a lipid bilayer, and is continuous with the endoplasmic reticulum. •The inside surface is linked to fibrous proteins that form a lattice-like sheet called the nuclear lamina. -Stiffens the membrane's structure and maintains its shape -Provides attachment points for each chromosome (The envelope contains thousands of openings called nuclear pores. -Function as doors into and out of the nucleus)

The Secretory Pathway Hypothesis

•The secretory pathway hypothesis proposes that proteins intended for secretion from the cell are synthesized and processed in a highly prescribed set of steps. •Proteins are packaged into vesicles when they move from the RER to the Golgi apparatus and from the Golgi apparatus to the cell surface. -The RER and Golgi apparatus function as an integrated endomembrane system.

How Dynamic Are Eukaryotic Cells?

•Your body's cells use, and synthesize, approximately 10 million ATP molecules per second. •Cellular enzymes can catalyze >25,000 reactions per second. •Each membrane phospholipid can travel the breadth of its organelle or cell in under a minute. •The hundreds of trillions of mitochondria inside you are replaced about every 10 days, for as long as you live. •The fluid plasma membrane's composition is constantly changing.