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Cellular Structure andChapter Functions 3 LOOKING AT CELLS Making sense of life’s most basic Unit Historical Ideas About Life • Before 1600 the predominant ideas about life revolved around the Spontaneous Generation Theory. • Spontaneous Generation is the idea that life appeared from nonliving matter (mold grows from cheese, mushrooms grow from dead wood) Historical Ideas About Life • The Spontaneous Generation Theory made sense to people because if they couldn’t see any mold, but overnight mold started growing on cheese, the mold must have appeared. • The Spontaneous Generation theory was slowly dismantled after the discovery of the cell. What is a Cell • Robert Hooke - 1665 - discovered cell with crude “microscope” – Observed cork cells – Used term “cell” reminding him of a Monk’s room or “cell” What is a Cell • Anton van Leeuwenhoek - 1674 Develops first quality microscope • In a pond water sample, Leeuwenhoek spotted “animacules” in his microscope. Formation of the Cell Theory • Once cells were discovered, scientists began finding them in all kinds of organisms. • Scientists began seeing cells before they were otherwise visible (mold spores, fly eggs, etc.) • After seeing this, it became harder to say life simply “appeared.” Cell Theory Scientists formed the cell theory in 1839, and revised it to the modern cell theory in 1855. The cell theory has three tenants. 1. All living things or organisms are made of cells and their products. 2. New cells are created when existing cells divide into two new cells. 3. Cells are the basic building units of all life. Cell Theory With the cell theory in place, biologists could start looking for cellular explanations of biology, instead of assuming that actions “just happened.” This new idea revolutionized modern biology and scientists began looking at cells and their structure in more detail to answer larger questions. One major modern addition to the cell theory important to biology students is the idea that: Cell Theory The activity of an organism depends on the total activity of independent cells. Cells perform actions – Ex. Heart cells contract so heart tissues contract, so the heart contracts, so blood is pumped, so other cells get nutrients and continue your bodily functions. (and live) At a basic level, all biology is based on what each cell is doing at any given time. Because of this, biologists began spending significant resources studying cells. Two General Categories of Cells The study of cells led to the discovery of two very different kinds of cells. These two cell types create all life. Eukaryotic cell - Cells with a nucleus and organelles Every living organism EXCEPT bacteria How do I remember? - Eu = True Karyote = Nucleus Two General Categories of Cells B. Prokaryotic Cells - Lack nucleus and organelles - Single celled organisms - Simple cells before other life formed. First life forms were prokaryotic. How do I remember? - Pro = Before - Sometimes we say pro = No - Karyote = Nucleus Prokaryotic Cells 1. Different kinds of bacteria are the only known organisms who have a prokaryotic structure. 2. If you are asked about prokaryotes, you are being asked about bacteria. 3. BACTERIA ONLY! Prokaryotic Cells 1. Prokaryotes are single celled. • They lack advance functioning because their cells cannot specialize. 2. These are the simplest form of cells and have fewer structures than eukaryotic cells. 3. Prokaryotic cells have 3 main parts. Prokaryotic Cells 1.Outer Structures • Pili (pl), Pilus (s) – Hairlike structures that surround prokaryotic cells for movement. • Flagella – Longer whip-like structure used for movement. There are typically many more cilia on a cell than flagella. Cilia usually line the entire outer surface of a cell, while there are usually only a few flagella and they are located on one end of the organism. Prokaryotic Cells 2. Wall Structures • Cell Wall – A tough layer made of protein that protects and supports the cell In modern bacteria, the cell wall is made of a protein matrix called peptidoglycan (important). When you take antibiotics, the reason they work is that the medicine breaks down peptidoglycan, making the cell explode. • Cell Membrane – A phospholipid bilayer that controls the movement of substances in and out of the cell. Polymer or Monomer? Prokaryotic Cells 3. Interior Structures • Cytoplasm – The gel-like substance that fills the majority of the inside of cells. Cytoplasm is 70%90% water and is usually clear. Break it down: Cyto – Cell Plasm – Substance The cytoplasm looks like nothing in drawings. It is just a space filler to allow other materials to “flow” around the cell. Remember: Empty-looking space is the cytoplasm. Prokaryotic Cells 3. Interior Structures • Ribosomes - A collection of RNA and protein that builds new proteins for the cell. Ribosomes are usually represented by small dots floating in the cytoplasm. They assemble amino acids into proteins by using the genetic code from DNA. This is called translation (We will spend a lot of time on this later). Prokaryotic Cells 3. Interior Structures • Nucleoid – The region of a cell (usually the center) that contains most or all of the genetic material in prokaryotic cells. Break it down: Nucleus – Central and most important part Oid (suffix) - means similar or like It is NOT a nucleus, but is similar (think humanoid: like a human in some ways, but not truly human) The nucleoid is really just a bunch of wound up circular DNA. Do not confuse bunched up DNA with a nucleus. Prokaryotic Cells Important things to remember: 1. All prokaryotes are bacteria and all bacteria are prokaryotes. 2. Prokaryotes do not have a nucleus 3. Prokaryotes do not have organelles 4. Prokaryotes DO have a cell wall (peptidoglycan) 5. Prokaryotes are small. (compared to Eukaryotes) Eukaryotic Cells 1. All other living organisms besides bacteria are eukaryotic. Animals, plants, fungi and protists (single celled water critters) are all eukaryotic. 2. The number one distinguishing feature of eukaryotes is the big ol’ nucleus. 3. NO BACTERIA! Eukaryotic Cells 1. Eukaryotes are single celled and multi-cellular. • Eukaryotic organisms can have very complicated bodies because their cells can specialize. (humans) 2. These are the most advanced cells and have many different cell parts. 3. Eukaryotic cells also have 3 main parts. Eukaryotic Cells Eukaryotes are incredibly diverse, so not all cells feature the same parts, but we will divide into these three sections 1. Cell Interior (2 parts) a) Membrane Bound Organelles b) Other Interior Components 2. Protection and Containment 3. Exterior Structures Eukaryotic Interior - Organelles 1. Cell Interior: Membrane Bound Organelles • Nucleolus – The center of the nucleus, made of protein and RNA, creates ribosomes. –olus suffix means “small” • Nucleus – The most visible organelle of the cell. Houses the cell’s DNA. The nucleus and nucleolus each have an extra phospholipid bilayer (membrane) for protection and separation from the rest of the cell. The nuclear membrane is sometimes called the nuclear envelope. All of the cell’s instructions (DNA) are found here. Eukaryotic Interior - Organelles 1. Cell Interior: Membrane Bound Organelles • Mitochondrion – The cell’s “powerhouse.” Makes Adenosine Triphosphate, or ATP; the molecule that is used for all cell functions. Mitochondria (plural) – Mitochondrion (singular) Mitochondria are usually represented by an oval shape with back and forth ridges inside. These ridges play a role in cellular respiration, the chemical process that makes ATP. Mitochondria are the most important cell organelle after the nucleus for eukaryotes. Eukaryotic Interior - Organelles 1. Cell Interior: Membrane Bound Organelles • Ribosomes - A collection of RNA and protein that builds new proteins for the cell. • Endoplasmic Reticulum (ER) – A membrane-like system of tubes, proteins and sacs that makes new membranes, and helps detoxify the cell. The ER is always located next to the nucleus and there are two types, Rough ER and Smooth ER. Rough ER has ribosomes located on it, (the small dots) while Smooth ER does not. Other than the presence of the ribosomes, the smooth ER will look quite similar to the rough ER. Eukaryotic Interior - Organelles 1. Cell Interior: Membrane Bound Organelles • Golgi Apparatus (Golgi Body) – Stacks or folds of membrane that “package” proteins to ship to other parts of the cell or to leave the cell. The Golgi Apparatus typically finishes protein structures created by the ribosome on the Endoplasmic Reticulum. The Golgi Apparatus is almost always floating in the cytoplasm away from the nucleus. In our drawing, proteins (macromolecules) are being shipped from the smooth ER to the Golgi Apparatus. The Golgi Apparatus also creates organelles called Lysosomes and helps to form lipid structures (membranes again) within the cell. Eukaryotic Interior - Organelles 1. Cell Interior: Membrane Bound Organelles • Lysosomes – A sac-like organelle that breaks down molecules within a cell. Lysosomes frequently “digest” food, waste, and worn out organelles. The name: lysis – to separate some – body; to separate a body (molecule). Lysosomes also move materials in and out of the cell, destroy invading bacteria and viruses, and sometimes kill their own cell. This gave them the nickname “suicide sacks.” Lysosomes contain hydrolase. What is hydrolase? Hydrolase is an enzyme that breaks down molecules by adding water. Eukaryotic Interior - Organelles 1. Cell Interior: Membrane Bound Organelles • Vesicles/Vacuoles – Membrane bound sacks that function as storage containers for materials inside the cell. Lysosomes are a version of a vesicle. Vesicles and Vacuoles have their own phospholipid bilayer that separates the contents from the inner cell environment. Vesicles and Vacuoles are considered organelles because they have the membrane. Vesicles are for transport of materials and Vacuoles are for storage of materials. – See drawing Eukaryotic Interior - Components 1. Cell Interior: Other Cellular Components • Cytoplasm – The same as in prokaryotes, the cytoplasm is the gel-like substance that fills the majority of the inside of cells. All organelles “float around” within the cytoplasm. • Cytoskeleton – A network of protein tubes and fibers that provide structure to the inside of the cell and hold the cell together. Cyto – Cell, Skeleton – Skeleton (duh) The Cytoskeleton is made of microfilaments and microtubules. The filaments (bone) are primarily for structure and the microtubules help move molecules around the cell (vessels). Eukaryotic Interior - Components 1. Cell Interior: Other Cellular Components • Centrioles – Technically part of the cytoskeleton, the centrioles are a bundle of microtubules that are used during cell division. (they look like churros) Centrioles attach to the chromosomes (DNA) in the nucleus and help to pull the cell apart. They usually just sit there when the cell isn’t dividing. During division, small spindle fibers attach to the chromosomes and centrioles. Eukaryotic Interior – Components Plant Specific 1. Cell Interior: Membrane Bound Organelles • Chloroplasts – The organelle that carries out photosynthesis in plants and protists. Chloroplasts give plants and protists their green color. Chloroplasts use sunlight, water and carbon dioxide to produce glucose (carbohydrate). Plastids – Any type of “plast” is a plastid. These organelles are responsible for photosynthesis in all organisms (even brown and red ones). Chloro is the green kind of plastid. • Central Vacuole - Plants also have larger vacuoles than other organisms for water storage. In many cases, the central vacuole is larger than the rest of the cell combined. Vacuoles help maintain the plant’s shape (they don’t have muscles). Plants begin to wilt when their vacuoles empty out. Eukaryotic Protection and Containment 2. Protection and Containment • Cell Membrane – Semi-permeable phospholipid bilayer that separates the cell from the outside environment. Also controls what materials go into and out of the cell. Without the cell membrane, the cell would simply be stuff floating in water. The cell membrane also contains protein groups, cholesterol and carbohydrate chains. The proteins assist molecules that could not otherwise pass through the membrane. (more on this later) The cellular envelope is present in ALL cells and has an almost identical structure across all organism types. Eukaryotic Protection and Containment 2. Protection and Containment • Cell Wall (Plants and Fungi ONLY) – Layer of rigid, tough material that helps protect and support the cell. The cell wall is typically thick. In plants the cell wall is made of cellulose (fiber) In fungi the cell wall is made of chitin (also found in crustacean shells or insect exoskeletons) The presence of the cell wall is what makes veggies crunch. You are shattering the cell walls with your teeth. Eukaryotic Exterior Structures 3. Exterior Structures – Found only in certain cells. • Flagella – Longer whip-like structure used for movement. Eukaryotic flagella function in roughly the same manner as prokaryotic flagella. Cilia (pl), Cilium (s) – Smaller projections used for sense or locomotion. Cilia are used by many types of cells sometimes as sense organs (touch or chemical), and sometimes to move (similar to prokaryotic pili) Labeled Prokaryote Labeled Animal Cell Labeled Plant Cell Cellular Structure andChapter Functions 3 LOOKING AT CELLS Making sense of life’s most basic Unit