Chapter 6- Cell Structure and Function - JENSEN BIOLOGY



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Unit 4, Part 1 Notes – Cell Structure and Function

AP Biology

1. What are the parts of the cell theory?

a. All living things are made of cells

b. Cells are the basic unit of structure and function

c. Cells are derived from existing cells (in other words, new cells are created from the division of old cells)

2. What are the different types of cells?

a. All cells fall into one of these two broad categories. Only the single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes—pro means before and kary means nucleus. Animals, plants, fungi, and protists are all eukaryotes—eu means true and again kary means nucleus—and are made up of eukaryotic cells (or in the case of protists, just one eukaryotic cell).

b. Components of prokaryotic cells: A prokaryote is a simple, single-celled organism that lacks a nucleus and membrane-bound organelles, meaning that prokaryotic cells are not divided up on the inside by membrane walls, but consist instead of a single open space.

c. Eukaryotic cells are more complex and have evolved to contain membrane-bound compartments called organelles that each have certain jobs.

d. The differences between prokaryotes and eukarotes is summarized in the table below.

|Prokaryotic Cells |Eukaryotic Cells |

|Have no nucleus that contains their DNA, but instead have a central |Have a nucleus where their DNA is contained within the nuclear |

|region called the nucleoid where the majority of their DNA is found. |membrane. |

|Have no membrane-bound organelles like mitochondria, vacuoles, or |Have many membrane-bound organelles that each perform a specific job |

|golgi bodies. |necessary to keep the cell alive |

|Have circular DNA |Have linear DNA |

|Have “70s” ribosomes (70s refers to a specific structure) |Have “80s” ribosomes (80s is a different structure than 70s) |

|Always have a cell wall |Some eukaryotes do have a cell wall (plants and fungi) while others do|

|Smaller |not (animals and protists) |

|Simpler |Larger |

|“Older” in the sense that they have been around longer |More complex |

| |“Newer” in the sense that they evolved more recently |

3. What traits are found all cells?

a. They are surrounded by plasma (cell) membrane.

b. They contain a semifluid substance called the cytosol and organelles (structures within the cell with specific functions)

c. Together the cytosol and the organelles make up the space between the membrane and the nucleus (called the cytoplasm)

d. They contain DNA

e. They have ribosomes (used to make proteins)

4. What size is a typical cell?

a. Prokaryotic cells are 1-10 µm (micrometers) in diameter – SEE IMAGE TO THE RIGHT

b. Eukaryotic cells are 10-100 µm in diameter – SEE IMAGES OF PLANT AND ANIMAL CELLS ON THE NEXT PAGE.

c. Cells cannot get too large because as they increase in size, their volume increases faster than their cell membrane surface area. In other words, their surface area to volume ratio decreases.

d. Because of this. large cells can’t transport food/oxygen/waste fast enough across their cell membranes to support the activities going on in the cell.

e. To solve this problem, large organisms have MORE cells; NOT BIGGER cells

f. Certain cell shapes (ex: intestinal cells containing membrane folds called microvilli) can increase the surface area of the membrane and therefore increase transport across the membrane –> SEE IMAGE TO THE RIGHT

Eukaryotic Cells

5. How are eukaryotic cells organized?

a. Eukaryotic cells have systems of internal membranes (made mostly of phospholipids and integral membrane proteins) to divide the cell into different compartments with different chemical conditions and different functions. For example, the mitochondrion has a specialized environment enclosed in two membranes in which the reactions of cellular respiration can be performed.

6. How is the nucleus (found in eukaryotic cells ONLY) organized?

a. The nucleus is surrounded by a double membrane with holes (i.e. nuclear pores) lined by special proteins to regulate the passage of molecules in and out of the nucleus

b. DNA exists within the nucleus as chromatin (DNA loosely coiled around proteins) or chromosomes (super-coiled/tightly packed DNA… formation of chromosomes only occurs prior to cell division)

c. At the middle of the nucleus is a dense sphere called the nucleolus which creates ribosomes

7. What is the structure, function, and location of ribosomes?

a. Ribosomes are made of proteins and RNA. They are one of the only organelles found in both eukaryotic and prokaryotic cells. They are not surrounded by a membrane.

b. Ribosomes are used to synthesize proteins

c. Ribosomes can be found suspended in the cytosol. These are called free ribosomes and they are used to create proteins that will be used in the cytosol. Ribosomes are also found attached to the Rough ER or nuclear envelope. These are called bound ribosomes and they are used to create proteins that are sent through the endomembrane system (Note: The structure and function of the endomembrane system will be described under #8) to a final destination to the cell membrane (ex: to become channel proteins or protein pumps). These proteins may also be exported from the cell to act as signaling molecules between cells (ex: hormones).

8. What is the endomembrane system and how is it used to send proteins out of the cell?

a. The endomembrane system is a network of organelles made of membrane. These organelles are all involved in synthesis, modification, or packaging of proteins to be sent from the cell.

b. Ribosomes on the rough endoplasmic reticulum (or rough ER for short) create proteins. These proteins enter the ER inner space (called the ER lumen) and may be modified by enzymes in this inner space. For example, certain proteins become attached to carbohydrate chains in the ER lumen. They are then called glycoproteins. Glycoproteins are used on the surface of the cell membrane to help cells recognize each other.

c. The proteins that have been created and modified travel to the Golgi apparatus via vesicles (small membrane sacs) that bud off of the ER and later fuse with the cis side of the Golgi. (Note: the Cis side of the Golgi is closer to the ER and farther from the cell membrane)

d. In the tubes/sacs of the Golgi (the cisternae), proteins are modified by more enzymes that can break off parts of proteins or add additional molecules on. These proteins are then packaged into new vesicles that bud off the trans side of the Golgi and later fuse with the cell membrane to release their contents outside of the cell. (Note: the Trans side of the Golgi is closer to the cell membrane and farther from the ER.)

9. What is the structure, function, and location of the endoplasmic reticulum?

a. The ER is a system of interconnected tubes and sacs of membranes. The space inside these tubes is called the ER lumen.

b. There are two parts to the ER – the Rough ER and the Smooth ER. The Rough ER is attached to the nuclear membrane and the smooth ER is further away from the nucleus.

c. The Rough ER has ribosomes attached and is particularly abundant in cells that secrete high amounts of proteins (because ribosomes make proteins!)

• Proteins created on the attached ribosomes are inserted into the ER lumen and folded into their 3D shape.

• Modifications (ex: addition of carbohydrate chains) may occur in the ER lumen before a protein is folded.

• Proteins that will be used in the cell membrane or protines that will be secreted from the cell (secretory proteins) are packaged into vesicles and sent to the Golgi from the rough ER. (Note: secretory proteins are proteins that will ultimately be secreted from / leave the cell)

• Because the Rough ER helps to move proteins around within the cell (i.e. intracellular transport), it is sometimes called the “highway of the cell”.

d. The Smooth ER does not have attached ribosomes.

• The Smooth ER is used to create phospholipids that can be used in the cell membrane or in the intracellular membranes that make up many organelles. To review what phospholipids are, go back to your Unit 2, Part 3 Notes on macromolecules.

• It contains enzymes for many different processes (ex: synthesizing oils, steroids, phospholipids – all types of lipids!). These enzymes are often made in the Rough ER (because enzymes are proteins!).

• Liver cells have a high amount of smooth ER because the smooth ER can also be used to break down toxins (ex: nitrogen waste from cells, drugs, alcohol)

• Muscle cells also have a high amount of smooth ER because the smooth ER can help store Ca++ ions to regulate muscle contraction

• Note: Frequent drug use leads to increased smooth ER for increased break down… increased amount of smooth ER is the reason why tolerance increases and higher dose is needed for same effect AND why frequent/extreme drug use leads to liver damage (i.e. cirrhosis)

10. What is the structure, function, and location of the Golgi apparatus?

a. The Golgi looks like a stack of pancakes or flattened membrane sacs called cisternae

b. Is considered the post office of the cell. It is where secretory proteins and other molecules destined to leave the cell are modified and packaged.

c. There is a large Golgi in the cells of the pancreas because they produce large amounts of hormones like glucagon and insulin that must be exported (sent) from the cell)

d. Products are modified as they pass from the cis to trans side. They are also sorted and packaged into vesicles.

e. The Golgi adds molecular ID tags to products to aid in sorting. Identifiers such as phosphate groups act like ZIP codes to identify a product’s final destination

11. What is the structure, function, and location of lysosomes?

a. Lysosomes are specialized vesicles (spheres of membrane) that contain hydrolytic (digestive) enzymes.

b. Originally, scientists thought that lysosomes were only found in animal cells. Now, however, there is evidence that they are also found in plant cells.

c. The digestive enzymes found in lysosomes are made by ribosomes on rough ER and are modified in Golgi. Lysosomes containing these enzymes bud off the Golgi.

d. The enzymes can hydrolyze (break down) food, whole cells, damaged cell parts, etc.

e. Lysosomes are an example of compartmentalization (maintaining separate environments in different parts of the cell in order to perform specific functions)

• Lysosomal enzymes work best at pH 5 (i.e. more acidic than the normal pH of the cell)

• If a lysosome ruptures, the enzymes are not very active in cytosol because the cytosol has a neutral pH (which is not the optimal pH for the enzymes). This helps to prevent accidental “self-digestion”.

• Massive rupture of many lysosomes at the same time may destroy a cell by self-digestion, which is called autophagy or apoptosis.

f. Lysosomes are used for the following functions:

• Digestion of food in unicellular (single-celled) organisms

• Recycling of cell’s organelles and macromolecules

• Programmed cell death (apoptosis) by massive rupture of many lysosomes at the same time. Programmed cell death (apoptosis) means that the cell is hard-wired to destroy itself at a certain point in time or in response to certain signals. Apoptosis is important during embryonic development in humans. Early in fetal development, the baby’s hands look like paddles without distinct fingers. Apoptosis occurs to kill off the cells between the fingers in order to sculpt them. Cells that are damaged may also give off a signal to self-destruct. Cancer cells and cells infected by HIV don’t respond to this signal, which is one of the reasons why they are so problematic.

g. Tay-Sachs is a genetic disorder in which people lack lysosomal enzymes needed to break down lipids, which results in accumulation of lipids in the brain (causing blindness, seizures, and eventually death)

12. What is the structure, function, and location of vacuoles?

a. Vacuoles are larger versions of vesicles (membrane-bound sacs with various functions)

b. Food vacuoles form by the engulfment of food particles by the cell membrane (which pinches in to form a membrane sac containing the food particles). These food vacuoles join / fuse with lysosomes so that the food particles can be digested.

c. Contractile vacuoles are found in freshwater protists (single celled eukaryotic organisms). They pump excess water out that enters from the outside freshwater via osmosis.

d. There is a large central vacuole in many mature plant cells used to store proteins, ions (ex: K+, Na+, Cl), pigments, defensive molecules (to defend the plant against herbivores), water, etc.

e. The large vacuole reduces the area of the cytosol, so the surface area / volume ratio of the cell increases

13. What is the structure, function, and location of mitochondria?

a. A double membrane surrounds the mitochondrion. The outer mitochondrial membrane is smooth. The inner mitochondrial membrane is folded to maximize surface area for the reactions of cellular respiration. The folds themselves are called cristae. More cristae means more space for electron transport chains consisting of membrane protein pumps and ATP synthase proteins. The different compartments between and inside the membranes of the mitochondrion are used for different steps of cellular respiration.

b. Aerobic cellular respiration involves breaking down sugars, fats, and other molecules in the presence of oxygen to generate ATP

c. Cells with high energy needs (EX: muscle cells) have large numbers of mitochondria.

14. What is the structure, function, and location of chloroplasts?

a. A double membrane surrounds the chloroplast. There are also stacks of membrane sacs/disks located inside the inner membrane. Individual disks are called thylakoids. A stack of disks is called a granum (plural = grana). The fluid filled spaced that surrounds the grana is called the stroma.

b. The different compartments between and inside membranes of the chloroplasts are used for different parts of the reactions of photosynthesis.

c. Photosynthesis involves the conversion of solar energy to chemical energy by using the energy from sunlight to convert carbon dioxide to glucose (C6H12O6).

15. What is the endosymbiotic theory?

a. The endosymbiotic theory (a.k.a. the theory of endosymbiosis) claims that small prokaryotic cells were engulfed by larger prokaryotic cells, shared a symbiotic relationship with the host cell, and eventually became organelles within the larger cells (ex: mitochondria and chloroplasts).

b. Example of symbiosis: A mitochondrion provided energy for the larger cell and the cell provided protection for the mitochondrion

c. The endosymbiotic theory says that the first eukaryotic cells (cells with membrane-bound organelles like mitochondria and chloroplasts) evolved from prokaryotic cells in this way.

d. Evidence for endosymbiosis:

• Mitochondria and chloroplasts are the only organelles besides nucleus with their own DNA and double membranes. Their DNA is circular like prokaryotes.

• Mitochondria and chloroplasts have their own ribosomes (but they are 70s like prokaryotes, rather than 80s like the ribosomes in the eukaryotic cell).

• The inner membranes of mitochondria and chloroplasts have enzymes and transport systems similar to bacterial cell membranes.

• Mitochondria and chloroplasts replicate on their own, and if they are removed from a eukaryotic cell, the cell cannot “grow them back.” The nucleus does not have the instructions for creating either organelle. Mitochondria and chloroplasts reproduce using binary fission, a process of cell division found in free-living bacteria.

16. What is the structure, function, and location of the cytoskeleton?

a. The similarities between the cytoskeleton in all eukaryotic cells provides evidence for the relatedness of all eukaryotic organisms.

b. The cytoskeleton is made of a network of protein fibers that extend throughout the cytoplasm. The three different types of protein fibers are microtubules (thick), intermediate filaments (medium), and microfilaments (thin).

c. The cytoskeleton provides mechanical support for organelles and maintains the cell’s shape from within.

d. Organelles can travel around the cell by moving around on cytoskeletal protein “tracks” (like train tracks).

e. In addition to the cytoskeleton, another set of organelles called centrioles are also made up of microtubules. They contain 9 sets of 3 microtubules arranges in a star like pattern (they look similar to churros!)

f. These centrioles can only be found in animal cells and aid in cell division.

17. What is the structure, function, and location of cilia and flagella?

a. These “hairs” or “tails” extend from the cell’s surface and are used for movement.

b. Cilia are short and numerous, whereas flagella are long and there are only one to three on each cell.

c. Cilia are only found on eukaryotic cells. They can be used by single-celled eukaryotes (protists) in rowing motions for movement.

d. Cilia can also be found on certain eukaryotic cells within multicellular organisms. For example, cilia on cells lining the respiratory tract in humans can be used to sweep dust and other particles that enter the respiratory tract toward the nostrils where it can be expelled with exhaled air.

e. Flagella are found on some single-celled prokaryotic and eukaryotic organisms. They are used in a corkscrew motion for movement.

f. They are also found on certain eukaryotic cells within multicellular organisms (for example, sperm cells have a flagellum so they can swim to the egg).

g. They are made of microtubules (like the microtubules found in the cytoskeleton) that are arranged in a 9+2 pattern (nine doublets/pairs of microtubules in a ring around a pair of microtubules in the center)

h. Motor (movement) proteins called “dynein arms” walk along microtubules and cause bending and movement of the cilia and flagella, which requires ATP

18. What is the structure, function, and location of the plant cell wall?

a. Note: Prokaryotes, fungi, and some protists (single-celled eukaryotes) also have cell walls.

b. The cell wall is used for the following: protection, support, and maintaining cell shape

c. The cell wall of plants is mostly made of the polysaccharide cellulose, whereas the cell wall of bacteria is made of the polysaccharide peptidoglycan, and the cell wall of fungi is made of the polysaccharide chitin

d. Plasmodesmata are holes / pores in the cell walls of two adjacent (neighboring) plant cells that connect their cytosols and allow water and other particles to pass freely from one plant cell to another to make a whole plant one continuous unit.

19. What is the structure, function, and location of the animal extracellular matrix (ECM)?

a. The extracellular matrix is located outside the cell membrane of animal cells.

• It is composed of glycoproteins (proteins with attached carbohydrate chains) secreted by the cell.

b. The most common ECM glycoprotein is collagen.

c. The ECM strengthens cells, and helps connects cells together so they can act as a unit (a group of cells with similar functions = a tissue).

20. What types of structures in the ECM connect cells together

a. Tight junctions and desmosomes (aka adhesion junctions) fasten cells together

b. Gap junctions act like plasmodesmata in plant cells and provide channels between adjacent cells to allow molecules to pass between cells.

21. How are eukaryotic cells arranged into larger structures within multicellular organisms?

a. Organisms with prokaryotic cells are always unicellular (aka single-celled). Prokaryotic organisms include bacteria and archaea. (We learned about these in Unit 1, Part 4 – Biodiversity and Classification)

b. Organisms with eukaryotic cells can be unicellular (ex: protists) or multicellular (ex: fungi, plants, and animals).

c. In a multicellular organism, specialized cells are grouped into tissues. (Note: specialized cells have a specific structure that allows them to perform a particular function. For example, human muscle cells, bone cells, and skin cells all have different structures and therefore functions.) Tissues are grouped into organs, and organs are grouped into organ systems.

d. An example of multicellular organization within humans…

• Muscle cells are grouped together to form muscle tissue, which is used for contraction/movement.

• Muscle tissue is organized to form larger structures like the heart (an organ), which contracts to pump oxygen-rich blood to the tissues of the body.

• The heart and associated structures (ex: blood vessels) work together to form the circulatory system (an organ system), which pumps and delivers oxygen-rich blood to the tissues of the body. The circulatory system also returns carbon dioxide-rich blood to the heart and later to the lungs for exhalation.

Notes Questions and Picture Labeling

1. Which cell structures are found in BOTH prokaryotic and eukaryotic cells?

2. Which cell structures are found only in plant cells? What about animal cells?

3. Where in an animal cell can DNA be found? (Remember: Some organelles other than the nucleus contain DNA!)

4. Where in a plant cell can DNA be found? (Remember: Some organelles other than the nucleus contain DNA!)

5. What is the overall function of the endomembrane system?

6. Label the endomembrane system image to the right with the following terms: Golgi, Vesicle, Ribosome, Rough ER

A = C =

B = D =

What is missing from the diagram to the right?

7. Label the organelles in the image below…

[pic]

What type of cell is this, and how do you know?

8. Label the organelles in the image below…

[pic]

What type of cell is this, and how do you know?

9. Identify the organelle that is used for each function given below.

________________________A. Used to regulate the transport of materials into and out of the cell.

________________________B. Used to digest food, old cell parts, etc. using enzymes.

________________________C. Used to capture solar energy and convert it to the chemical energy stored in the molecule glucose.

________________________D. A network of proteins inside the cell that provide structural support for the cell.

________________________E. Structures made of microtubules that are used for movement… they are short and numerous on the outside of the cell.

________________________F. Structures made of microtubules that are used for movement… they are long and there are usually 1-3 of them on the outside of a cell.

________________________G. A structure that contains the cell’s DNA and has a double membrane.

________________________H. A structure within the nucleus that creates ribosomes.

________________________I. A structure used to create proteins that is found in both prokaryotic and eukaryotic cells.

________________________J. The region between the nucleus and cell membrane that contains a jelly-like fluid used to cushion organelles.

________________________K. A structure made of membrane with attached ribosomes that is used to create proteins that will exit the cell (aka secretory proteins). This structure also serves as a highway to move substances around the cell.

________________________L. A structure made of membranous tubes and sacs that is used to modify and package protein products and send them to the cell membrane.

________________________M. A structure made of membrane with no attached ribosomes that is used to create lipids (ex: steroid hormones) and remove / destroy toxins.

________________________N. A structure found on the outside of plant cells that is used to provide protection and support.

________________________O. A structure found only inside animal cells that is used to assist with cell division.

________________________P. A structure that is used to convert glucose into ATP.

________________________Q. A structure that is used to store substances (ex: water, food, wastes, enzymes).

________________________R. A network of glycoproteins outside animal cells that strengthens them and connects them to one another.

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