Unit 2 Section 3: Structure and Function of Cells (2024)

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Unit 2 Section 3: Structure and Function of Cells

Cell Organization
The eukaryotic cell can be divided into two major parts: the nucleus and the cytoplasm. The cytoplasm is the fluid portion of the cell outside the nucleus. Prokaryotic cells have cytoplasm as well, even though they do not have a nucleus.

Many cellular structures act as if they are specialized organs. These structures are known as organelles, literally “little organs.” Understanding what each organelle does helps us to understand the cell as a whole.

Comparing the Cell to a Factory
The eukaryotic cell is much like a living version of a modern factory. The specialized machines and assembly lines of the factory can be compared to the different organelles of the cell. Cells, like factories, follow instructions and produce products.
The Nucleus

In the same way that the main office controls a large
factory, the nucleus is the control center of the cell. The nucleus
contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules.
Chromosomes contain the genetic information that is passed from one generation of cells to the next. Most of the time, the threadlike chromosomes are spread throughout the nucleus in the form of chromatin—a complex of DNA bound to proteins.
The nucleus is surrounded by a nuclear envelope composed of two membranes. The nuclear envelope is dotted with thousands of nuclear pores, which allow material to move into and out of the nucleus.
Most nuclei also contain a small, dense region known as the nucleolus. The nucleolus is where the assembly of ribosomes begins.

Organelles That Store, Clean-up, and Support
1.Vacuoles- storage3. Lysosomes- clean up
2. Vesicles – storage and shipment4. Cytoskeleton – support
Vacuoles and Vesicles
Many cells contain large, saclike, membrane-enclosed structures called vacuoles that store materials such as water, salts, proteins, and carbohydrates.
Plant cells - single, large central vacuole filled with liquid. The pressure of the central vacuole in these cells increases their rigidity.

Animals cells - unicellular organisms (ex. Paramecium) By contracting rhythmically, this specialized vacuole pumps excess water out of the cell.
Nearly all eukaryotic cells contain smaller membrane-enclosed structures called vesicles. Vesicles are used to store and move materials between cell organelles, as well as to and from the cell surface.

Lysosomes

Lysosomes are small organelles filled with enzymes that function as the cell’s cleanup crew. One function of lysosomes is the breakdown of lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell. Lysosomes are also involved in breaking down organelles that have outlived their usefulness.

Cytoskeleton

Eukaryotic cells are given their shape and internal organization by a network of protein filaments known as the cytoskeleton. Certain parts of the cytoskeleton also help to transport materials between different parts of the cell, much like conveyer belts that carry materials from one part of a factory to another.

Cytoskeleton creates cilia and flagella in cells that require movement.

Microtubules
In animal cells, structures known as centriolesare also formed from tubulins. Centrioles are located near the nucleus and help to organize cell division. Centrioles are not found in plant cells.

Organelles That Build Proteins

1.Ribosomes- assembly

2. Endoplasmic Reticulum- assembly with destination outside of the cell

3. Golgi Apparatus- modify, package, shipment

4. Nucleus- brains of the operation

• Cells need to build new molecules all the time, especially proteins, which catalyze chemical reactions and make up important structures in the cell.
  
• Because proteins carry out so many of the essential functions of living things, a big part of the cell is devoted to their production and distribution.
  
• Proteins are synthesized on ribosomes, sometimes in association with the rough endoplasmic reticulum in eukaryotes.

Ribosomes

Ribosomes are small particles of RNA and protein found throughout the cytoplasm in all cells. Ribosomes produce proteins by following coded instructions that come from DNA. Each ribosome is like a small machine in a factory, turning out proteins on orders that come from its DNA “boss.”

Endoplasmic Reticulum

Eukaryotic cells contain an internal membrane system known as the endoplasmic reticulum, or ER. The endoplasmic reticulum is where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell.

Rough ER
The portion of the ER involved in the synthesis of proteins is called rough endoplasmic reticulum, or rough ER. It is given this name because of the ribosomes found on its surface. Newly made proteins leave these ribosomes and are inserted into the rough ER, where they may be chemically modified.

Smooth ER

The other portion of the ER is known as smooth endoplasmic reticulum (smooth ER) because ribosomes are not found on its surface. In many cells, the smooth ER contains collections of enzymes that perform specialized tasks, including the synthesis of membrane lipids and the detoxification of drugs.

Golgi Apparatus

Proteins produced in the rough ER move next into the Golgi apparatus, which appears as a stack of flattened membranes. The proteins are bundled into tiny vesicles that bud from the ER and carry them to the Golgi apparatus.

The Golgi apparatus modifies, sorts, and packages proteins and other materials from the ER for storage in the cell or release outside the cell. It is somewhat like a customization shop, where the finishing touches are put on proteins before they are ready to leave the “factory.” From the Golgi apparatus, proteins are “shipped” to their final destination inside or outside the cell.

Organelles That Capture and Release Energy

1. Chloroplast - solar panels and cafeteria

2. Mitochondria – power houses

Chloroplast

Plants and some other organisms contain chloroplasts. Chloroplasts are the biological equivalents of solar power plants. They capture the energy from sunlight and convert it into food that contains chemical energy in a process called photosynthesis.

*NOTE: Chloroplasts DO NOT MAKE ENERGY- they make sugar which is used by the mitochondria to make chemical energy.
Mitochondria
Nearly all eukaryotic cells, including plants, contain mitochondria. Mitochondria are the power plants of the cell. They convert the chemical energy stored in food into energy-rich compounds that are more convenient for the cell to use. This is called: cellular respiration!

Cell Boundaries

Similarly, cells are surrounded by a barrier known as the cell membrane. Many cells, including most prokaryotes and plant cells, also produce a strong supporting layer around the membrane known as a cell wall.

Cell Walls

The main function of the cell wall is to provide support and protection for the cell. Prokaryotes, plants, algae, and fungi have cell walls. Animal cells do not have cell walls.

Cell walls lie outside the cell membrane and most are porous enough to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily.

Cell Membranes

All cells contain a cell membrane that regulates what enters and leaves the cell and also protects and supports the cell. A double-layered sheet called a lipid bilayer, a flexible structure and forms a strong barrier between the cell and its surroundings.

The Properties of Lipids

Many lipids have oily fatty acid chains attached to chemical groups that interact strongly with water. The fatty acid portions of such a lipid are hydrophobic, or “water-hating,” while the opposite end of the molecule is hydrophilic, or “water-loving.”

The head groups of lipids in a bilayer are exposed to water, while the fatty acid tails form an oily layer inside the membrane from which water is excluded.

The Fluid Mosaic Model

Most cell membranes contain protein molecules that are embedded in the lipid bilayer. Carbohydrate molecules are attached to many of these proteins.

Because the proteins embedded in the lipid bilayer can move around and “float” among the lipids, and because so many different kinds of molecules make up the cell membrane, scientists describe the cell membrane as a “fluid mosaic.”

Some of the proteins form channels and pumps that help to move material across the cell membrane. Many of the carbohydrate molecules act like chemical identification cards, allowing individual cells to identify one another.

• Although many substances can cross biological membranes, some are too large or too strongly charged to cross the lipid bilayer.

• If a substance is able to cross a membrane, the membrane is said to be permeable to it.

• A membrane is impermeable to substances that cannot pass across it.

• Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot. Selectively permeable membranes are also called semipermeable membranes.

Answer Key

Cells and Their Organelles

The cell is the basic unit of life. The following is a glossary of animal cell terms. All cells are surrounded by a cell membrane. The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others. It is composed of a double layer of phospholipids and embedded proteins. Plant cells have an additional layer surrounding them called the cell wall. The cell wall is made of nonliving materials called cellulose. The centrosome (also called the :microtubule organizing center”) is a small body located near the nucleus. The centrosome is where microtubules are made. During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. The centriole is the dense center of the centrosome. Only animal cells have centrosomes. Microtubules are shaped like soda straws and give the nucleus its shape.

1. At what level of organization does life begin? cellular
2. What surrounds all cells? Cell membrane
3. What is meant by semipermeable? Some substances are able to pass into the cell, but not everything.
4. What 2 things make up the cell membrane? Phospholipids and embedded proteins
5. The cell membrane is also called the __p______l__ ___a__ __s___ __m______a__ membrane.
6. Centrioles are found inside of what type of cell? animal
7. What additional layer is found around the outside of plant cells and bacteria? Cell wall
8. Centrioles are found at the center of the

___c__ __e___ __n___ __t___ __r___ __o______s__ __o___ __m___ __e___.

The nucleus in the center of a cell is a spherical body containing the nucleolus that makes ribosomes. The nucleus controls many of the functions of the cell (by controlling protein synthesis). It also contains DNA assembled into chromosomes. The nucleus is surrounded by the nuclear membrane. Materials can move from the nucleus to the cytoplasm through nuclear pores in the membrane around the nucleus. Cytoplasm is the jellylike material outside the cell nucleus in which the organelles are located. All cells, even prokaryotes contain small bodies called ribosomes. Proteins are made here by a process called protein synthesis.

1. Where is DNA found inside a cell? nucleus
2. What cell process is controlled by the nucleus? Protein synthesis
3. DNA coils tightly during division and assembles into visible

___c__ __h___ _r______o___ __m___ __o___ __s___ __o___ __m______e__ ___s__

1. Where are organelles located? cytoplasm
2. Where are proteins made in a cell? ribosomes
3. Do all cells need ribosomes? yes
4. The process of making proteins is called. Protein synthesis

Rough endoplasmic reticulum (rough ER) is a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell’s cytoplasm. The ER is continuous with the outer nuclear membrane. Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transports materials through the cell and produces proteins in sacks called cristern which are sent to the Golgi body, or inserted into the layered, sac-like organelle that looks like a stack of pancakes. The Golgi body modifies and packages proetins and carbohydrates into membrane-bound vesicles for “export” from the cell. Smooth ER does NOT have ribosomes on its surface. It makes proteins and lipids that will be exported by the cell. It also controls the calcium level in muscles and detoxifies poisons, alcohol, and drugs.

1. How does rough ER differ from smooth ER? The rough ER is covered with ribosomes and the smooth ER does not have ribosomes on it.
2. Rough ER is connected to the___nuclear______membrane and to the ______smooth______ER.
3. Proteins made by rough ER travel to the Golgi in sacks called ______vesicles______. Golgi ____modifies______and _packages______proteins for export out of the cell.
4. Give 3 jobs of the smooth ER.
5. __make lipids______
6. ______makes proteins______
7. _controls the calcium level in muscles and detoxifies poisins, alcohol and drugs______

Chloroplasts are elongated or disc- shaped organelles containing chlorophyll that trop sunlight for energy. Photosynthesis (in which energy from sunlight is converted into chemical energy- food) takes place in the chloroplasts. Only plant cell, not animal cells, can make their own food. Cells also contain fluid-filled sacs called vacuoles. The vacuole fills with food being digested and waste material that is on its way out of the cell. In plant cells, a large central vacuole takes up most of the space in the cell. Mitochondria are spherical to rod-shaped organelles with a double membrane. The inner membrane is infolded many times, forming a series of projections called cristae. The mitochondrion converts the energy stored in glucose into ATP (adenosine triphosphate) for the cell. Both plant and animal cells have double membranes and their own DNA. Cells also contain spherical organelles called lysosomes that contain digestive enzymes. Nutrients are digested by the cell here, as well as, old cell organelles that are going to be recycled.

1. What process takes place inside chloroplasts? photosynthesis
2. What is the energy for this process? sunlight
3. What pigments traps the energy? chlorophyll
4. Chloroplasts are found in what type of cell(s)? plant
5. Both chloroplasts and mitochrondria are lake in that they both have __double______membranes and their own DNA.
6. Food, water, and wastes are stored inside _vacuoles______.
7. Digestion takes place inside ____lysosmes______containing __digestive enzymes______.
8. The largest organelle in plants is the ______central vacuole______
9. What organelle breaks down and recycles worn out cells? ______lysosome______