Cells: The Basic Units of Life Section 1: The Diversity of Cells.
Cells: The Working Units of Life
description
Transcript of Cells: The Working Units of Life
Cells: The WorkingUnits of Life
4
History of the Cell
Hooke – coined the term “cell”
Leewenhoek – bacteria are made of cells & first good microscope!
Concept 4.1 Cells Provide Compartments for Biochemical Reactions
Cell theory was the first unifying theory of biology.
1. Cells are the basic units of life.
2. Cells are the basic units of structure and function.
3. All cells come from preexisting cells.
Animal Cells
Concept 4.1 Cells Provide Compartments for Biochemical Reactions
Most cells are tiny
• to maintain a good surface area-to-volume ratio.
Figure 4.2 Why Cells Are Small
Figure 4.1 The Scale of Life
Concept 4.1 Cells Provide Compartments for Biochemical Reactions
To visualize small cells, there are two types of microscopes:
Light microscopes—use glass lenses and light
Resolution = 0.2 μm (OK)
Electron microscopes—electromagnets focus an electron beam
Resolution = 2.0 nm (awesome)
Figure 4.3 Microscopy
Concept 4.1 Cells Provide Compartments for Biochemical Reactions
The plasma membrane:
• Is a selectively permeable barrier that allows cells to maintain a constant internal environment
• Is important in communication and receiving signals
• Often has proteins for binding and adhering to adjacent cells
4.1 CelConcept 4. Provide Compartments for Biochemical Reactions
Two types of cells: Prokaryotic and eukaryotic
Prokaryotes are without membrane-enclosed compartments. NO NUCLEUS!
Eukaryotes have membrane-enclosed compartments called organelles, such as the nucleus.
In-Text Art, Ch. 4, p. 59
Concept 4.2 Prokaryotic Cells Do Not Have a Nucleus
Prokaryotic cells:
• Are enclosed by a plasma membrane
• Have DNA located in the nucleoid
The rest of the cytoplasm consists of:
• Cytosol (water and dissolved material) and suspended particles
• Ribosomes—sites of protein synthesis
Figure 4.5 A Prokaryotic Cell
Concept 4.2 Prokaryotic Cells Do Not Have a Nucleus
Other Characteristics of a prokaryote:
• rigid cell wall (containing peptidoglycan) outside the plasma membrane.
• Some bacteria have an additional outer membrane that is very permeable.
Other bacteria have a slimy capsule made of polysaccharides.
Some prokaryotes swim by means of flagella, made of the protein flagellin
Figure 4.6 Prokaryotic Flagella (Part 1)
Figure 4.7 Eukaryotic Cells (Part 1)
Figure 4.7 Eukaryotic Cells (Part 8)
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Ribosomes—sites of protein synthesis:
both prokaryotic and eukaryotic cells
similar structure—one larger and one smaller subunit.
Ribosomes are not membrane-bound organelles—in eukaryotes, they are free in the cytoplasm, attached to the endoplasmic reticulum, or inside mitochondria and chloroplasts.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
The nucleus is usually the largest organelle.
It is the location of DNA and of DNA replication.
It contains the nucleolus, where ribosomes are made
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
The nucleus is surrounded by two membranes that form the nuclear envelope.
Nuclear pores in the envelope control movement of molecules between nucleus and cytoplasm.
In the nucleus, DNA combines with proteins to form chromatin in long, thin threads called chromosomes.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, and lysosomes.
Tiny, membrane-surrounded vesicles shuttle substances between the various components, as well as to the plasma membrane.
Figure 4.8 The Endomembrane System
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Endoplasmic reticulum (ER)—network of interconnected membranes in the cytoplasm, with a large surface area
Two types of ER:
• Rough endoplasmic reticulum (RER)
• Smooth endoplasmic reticulum (SER)
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Rough endoplasmic reticulum (RER) has ribosomes attached to begin protein synthesis.
Newly made proteins enter the RER lumen.
Once inside, proteins are chemically modified and tagged for delivery.
The RER participates in the transport.
All secreted proteins and most membrane proteins, including glycoproteins, which is important for recognition, pass through the RER.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Smooth endoplasmic reticulum (SER)—more tubular, no ribosomes
It chemically modifies small molecules such as drugs and pesticides.
It is the site of glycogen degradation in animal cells.
It is the site of synthesis of lipids and steroids.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
The Golgi apparatus is composed of flattened sacs (cisternae) and small membrane-enclosed vesicles.
Receives proteins from the RER—can further modify them
Concentrates, packages, and sorts proteins
Adds carbohydrates to proteins
Site of polysaccharide synthesis in plant cells
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
The Golgi apparatus has three regions:
The cis region receives vesicles containing protein from the ER.
At the trans region, vesicles bud off from the Golgi apparatus and travel to the plasma membrane or to lysosomes.
The medial region lies in between the trans and cis regions.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Primary lysosomes originate from the Golgi apparatus.
They contain digestive enzymes, and are the site where macromolecules are hydrolyzed into monomers.
Figure 4.9 Lysosomes Isolate Digestive Enzymes from the Cytoplasm (Part 1)
Figure 4.9 Lysosomes Isolate Digestive Enzymes from the Cytoplasm (Part 2)
Figure 4.7 Eukaryotic Cells
Outer Membrane (very porous)
Cristae – increases Surface Area-
Matrix – Enzymes, DNA, Ribosomes
Figure 4.7 Eukaryotic Cells
Thylakoids – chlorophyll
Grana – stack of thylakoids
Stroma - aqueous
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Peroxisomes collect and break down toxic by-products of metabolism, such as H2O2, using specialized enzymes.
Glyoxysomes, found only in plants, are where lipids are converted to carbohydrates for growth.
Concept 4.3 Eukaryotic Cells Have a Nucleus and Other Membrane-Bound Compartments
Vacuoles :
• Storage of waste products, food, enzymes, water, and pigments
• creates turgor pressure in plant cells
Contractile vacuoles in freshwater protists get rid of excess water