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What is the primary difference between prokaryotic and eukaryotic cells?
What is the primary difference between prokaryotic and eukaryotic cells?
What is the minimum size of an object that can be observed using a light microscope?
What is the minimum size of an object that can be observed using a light microscope?
What is the name of the darkened region in the central part of a prokaryotic cell where the DNA is found?
What is the name of the darkened region in the central part of a prokaryotic cell where the DNA is found?
What is the function of organelles in eukaryotic cells?
What is the function of organelles in eukaryotic cells?
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What is the term for the study of the structure and function of cells?
What is the term for the study of the structure and function of cells?
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What is the primary function of ribosomes in cells?
What is the primary function of ribosomes in cells?
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What is the name of the living part of the cell?
What is the name of the living part of the cell?
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What is the main component of the cytosol?
What is the main component of the cytosol?
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What is the resolution of an electron microscope?
What is the resolution of an electron microscope?
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What is the function of the nuclear pores in the nuclear envelope?
What is the function of the nuclear pores in the nuclear envelope?
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What is the composition of protoplasm?
What is the composition of protoplasm?
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What is the combination of DNA and proteins in the nucleus called?
What is the combination of DNA and proteins in the nucleus called?
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Where are attached ribosomes typically found?
Where are attached ribosomes typically found?
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What is the function of the nucleolus in the nucleus?
What is the function of the nucleolus in the nucleus?
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What is the primary difference between free and attached ribosomes?
What is the primary difference between free and attached ribosomes?
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What is the percentage of water in the cytosol?
What is the percentage of water in the cytosol?
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What is the primary function of the plasma membrane in terms of the cell's external environment?
What is the primary function of the plasma membrane in terms of the cell's external environment?
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What is the role of aquaporins in the plasma membrane?
What is the role of aquaporins in the plasma membrane?
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What is the composition of the phospholipid bilayer in the plasma membrane?
What is the composition of the phospholipid bilayer in the plasma membrane?
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What is the function of carbohydrates in the plasma membrane?
What is the function of carbohydrates in the plasma membrane?
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What type of molecules can pass through the plasma membrane easily?
What type of molecules can pass through the plasma membrane easily?
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What is the term used to describe the plasma membrane's ability to allow certain molecules and ions to enter and exit the cytoplasm freely?
What is the term used to describe the plasma membrane's ability to allow certain molecules and ions to enter and exit the cytoplasm freely?
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What is the main component of the fluid present in the cell and surrounded by the cell membrane?
What is the main component of the fluid present in the cell and surrounded by the cell membrane?
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What is the location of the nucleus within the cytoplasm?
What is the location of the nucleus within the cytoplasm?
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What is the primary function of the Golgi complex?
What is the primary function of the Golgi complex?
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Which organelle is responsible for breaking down and recycling cellular waste?
Which organelle is responsible for breaking down and recycling cellular waste?
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What is the term for the process by which a lysosome breaks down and recycles parts of a cell?
What is the term for the process by which a lysosome breaks down and recycles parts of a cell?
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What is the primary function of mitochondria?
What is the primary function of mitochondria?
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What is the term for the process by which a cell takes in large molecules from the outside environment?
What is the term for the process by which a cell takes in large molecules from the outside environment?
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What is the term for the process by which a cell releases large molecules from the inside to the outside environment?
What is the term for the process by which a cell releases large molecules from the inside to the outside environment?
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Which organelle is responsible for modifying and packaging proteins produced in the RER?
Which organelle is responsible for modifying and packaging proteins produced in the RER?
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What is the type of transport that uses vesicles rather than channel or transport proteins?
What is the type of transport that uses vesicles rather than channel or transport proteins?
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What is the primary function of the Golgi complex in a cell?
What is the primary function of the Golgi complex in a cell?
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Which type of endocytosis involves the ingestion of solid particles, such as bacteria or dead cell remnants?
Which type of endocytosis involves the ingestion of solid particles, such as bacteria or dead cell remnants?
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What is the main difference between passive transport and facilitated transport?
What is the main difference between passive transport and facilitated transport?
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What is the primary mechanism by which lipid-soluble molecules enter a cell?
What is the primary mechanism by which lipid-soluble molecules enter a cell?
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Which type of transport involves the movement of molecules from an area of higher concentration to an area of lower concentration?
Which type of transport involves the movement of molecules from an area of higher concentration to an area of lower concentration?
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What is the function of a transporter protein in facilitated transport?
What is the function of a transporter protein in facilitated transport?
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Which type of endocytosis involves the binding of specific substances to plasma membrane receptors?
Which type of endocytosis involves the binding of specific substances to plasma membrane receptors?
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What is the direction of molecule movement during facilitated transport?
What is the direction of molecule movement during facilitated transport?
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Study Notes
Cell Structure and Function
- Cells are the basic structural and functional units of life, and all organisms are composed of either one cell (unicellular) or more cells (multicellular).
- The branch of biology that deals with the structure and function of cells is called Cytology.
- Cells are classified into two groups: prokaryotes and eukaryotes, with the primary difference being the presence or absence of a nucleus, a membrane-bound structure that houses the DNA.
Prokaryotes vs Eukaryotes
- Prokaryotes are unicellular microorganisms that have no nuclear membrane or any other membrane-bound organelles (e.g. bacteria).
- Prokaryotic DNA is found in the central part of the cell, a darkened region called the nucleoid.
- Prokaryotes have a cell wall similar to plant cells.
- Eukaryotic cells are cells that contain a membrane-bound nucleus and other membrane-bound compartments called organelles, which have specialized functions (e.g. animals, plants, and fungi).
Cell Size and Shape
- Cells come in different sizes and shapes, but most cells are very small and require a microscope to examine.
- The size and shape of cells can vary greatly, with some cells having cube-shaped, long column-shaped, spindle-shaped, or having long projections.
Cell Structures
Protoplasm
- The living part of the cell is called protoplasm, which is composed of water, proteins, lipids, carbohydrates, and electrolytes.
- Protoplasm consists of two distinct regions: cytoplasm, which lies outside the nucleus, and nucleoplasm, which lies inside the nucleus.
- Cells also contain inclusions, which consist of metabolic by-products, storage forms of various nutrients and pigments.
Three Main Components of Cells
- Plasma membrane: an outer membrane that separates the cell's interior from its surrounding environment.
- Cytoplasm: the fluid present in the cell and surrounded by the cell membrane, which contains water, enzymes, salts, and various organelles.
- Nucleus: a large organelle that may or may not be centrally located within the cytoplasm.
Plasma Membrane
Principal Components
- Phospholipid bilayer: a "sandwich" made of two layers of phospholipids, with polar phosphate molecules forming the top and bottom surfaces, and nonpolar lipid tails in between.
- Proteins: scattered throughout the plasma membrane, playing important roles in allowing substances to enter the cell.
- Carbohydrates: attached to some of the lipids (glycolipids) and proteins (glycoproteins), forming specialized sites on the cell surface that allow cells to recognize each other.
Functions
- Isolates the interior of the cell from the external environment (physical barrier).
- Allows only certain molecules and ions to enter and exit the cytoplasm freely, making it selectively permeable.
Cytoplasm and Its Organelles
- The cytoplasm includes the contents of a cell between the plasma membrane and the nuclear envelope.
- It contains organelles and cytoskeleton suspended in the gel-like cytosol, which consists of 70-80% water.
- Many metabolic reactions, including protein synthesis, take place in the cytoplasm.
Nucleus
- A prominent structure in eukaryotic cells, the nucleus is a large organelle that may or may not be centrally located within the cytoplasm.
- It is enveloped in a double membrane called the nuclear envelope, which has nuclear pores to control the passage of ions, molecules, and RNA between the nucleoplasm and the cytoplasm.
- It stores genetic information as DNA organized into linear structures called chromosomes.
- Most nuclei contain at least one nucleolus, which consists of ribonucleic acid (RNA) and helps in producing structures called ribosomes.
Ribosomes
- Organelles composed of proteins and rRNA (nucleoproteins), where protein synthesis occurs.
- Ribosomes exist as free ribosomes within the cytoplasm or attached to the membrane of the endoplasmic reticulum.
Golgi Complexes
- Located near the nucleus in most cells, the Golgi complex consists of many smooth membranous saccules, some vesicular, others flattened, containing enzymes and proteins being processed.
- It completes posttranslational modifications of proteins produced in the RER and then packages and addresses these proteins to their proper destinations.
Lysosomes
- Membranous sacs produced by the Golgi apparatus, containing hydrolytic enzymes.
- Found in all cells of the body, but particularly numerous in white blood cells that engulf disease-causing microbes.
- When a lysosome fuses with such an endocytic vesicle, its contents are digested by lysosomal enzymes into simpler subunits, which then enter the cytoplasm.
Mitochondria
- Often called the powerhouses or energy factories of a cell, as they are responsible for making adenosine triphosphate (ATP), the cell's main energy-carrying molecule.
- Mitochondria are oval-shaped, double-membrane organelles, with an outer membrane enclosing the intermembrane space, and an inner membrane with many folds (cristae) enclosing a gel-like matrix.
- Abundant in cells or cytoplasmic regions where large amounts of energy are expended.
Mechanisms of Transport Across the Plasma Membrane
Bulk Transport (Vesicular Transport)
- Cells use bulk transport to move large molecules, such as polysaccharides or polypeptides, across the membrane.
- These processes use vesicles rather than channel or transport proteins.
- Includes exocytosis and endocytosis.
Diffusion
- The random movement of molecules from an area of higher concentration to an area of lower concentration, until they are equally distributed.
- A passive way for molecules to enter or exit a cell, requiring no energy to move substances.
Facilitated Transport
- Many solutes do not simply diffuse across a plasma membrane, but are transported by means of protein carriers within the membrane called transporters, which bind only to a particular molecule, such as glucose.
- During facilitated transport, a molecule is transported across the plasma membrane from the side of higher concentration to the side of lower concentration.
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Test your knowledge of cell structure and function, covering topics such as cytology, unicellular and multicellular organisms, and more.
