Cells and Their Functions
Cells and Their Functions
Overview
- Microscopes
- Cell Structure
- Membrane
- Protein Transport
- Synthesis
- Cell Division
- Cancer
- Mutations
- Metastases
- Causes
- Plasma Membrane
- Nucleus
- Cytoplasm
- Surface Projections
- Meiosis
- Mitosis
- DNA, RNA Structure
- Transcription
- Translation
Key Terms
- Active Transport
- Filtration
- Mitosis
- Cancer
- Gene Mutation
- Carcinogen
- Hemolysis
- Nucleus
- Chromosome
- Hypertonic
- Organelle
- Cytology
- Hypotonic
- Osmosis
- Cytoplasm
- Interphase
- Phagocytosis
- Diffusion
- Isotonic
- Plasma Membrane
- DNA
- Micrometer
- Ribosome
- Endocytosis
- Exocytosis
- Mitochondria
Chapter 3 Key Ideas
- Introduces the key idea of genes and proteins.
The Cell
- Cytology: The study of cells.
- The Cell: The basic unit of life.
- Shows life characteristics:
- Organization
- Metabolism
- Responsiveness
- Homeostasis
- Growth
- Reproduction
Microscopes
Learning Objectives
- List three types of microscopes used to study cells:
- Compound Light Microscope
- Transmission Electron Microscope
- Scanning Electron Microscope
Microscopy
- Microscope: An instrument that magnifies structures not visible to the naked eye.
Cell Structure
Learning Objectives
- Describe the composition and functions of the plasma membrane.
- Describe the cytoplasm of the cell and cite the names and functions of the main organelles.
Movement of Substances Across the Plasma Membrane
Learning Objectives
- Describe methods by which substances enter and leave cells that do not require chemical energy.
- Explain what will happen if cells are placed in solutions with concentrations the same as or different from those of the cytoplasm.
- Describe methods by which substances enter and leave cells that require chemical energy.
Protein Synthesis
Learning Objectives
- Describe the composition, location, and function of the DNA in a cell.
- Compare the functions of three types of RNA in cells.
- Explain briefly how cells make proteins.
Cell Division
Learning Objectives
- Name and briefly describe the stages in mitosis.
Cells and Cancer
Learning Objectives
- Discuss the cellular changes that may lead to cancer, and list several cancer risk factors.
Case Study
Learning Objectives
- Use the case study to explain how a small change in DNA sequence can impact the entire organism.
Word Anatomy
Learning Objectives
- Show how word parts are used to build words related to cells and their functions.
General Cell Organization
- Plasma Membrane
- Nucleus
- Cytoplasm
- Cytosol
- Organelles
Plasma Membrane
- Encloses cell contents
- Regulates what enters and leaves cell
- Participates in many cell activities (e.g., growth, reproduction, cell-to-cell interactions).
Plasma Membrane Components
- Phospholipid Bilayer
- Cholesterol
Plasma Membrane Proteins
Table 3-1: Types of Protein in the Plasma Membrane and Their Functions
- Channels: Pores in the membrane that allow passage of specific substances, such as ions.
- Transporters: Proteins that change shape as they shuttle substances, such as glucose, across the membrane.
- Receptors: Allow for attachment of substances, such as hormones, to the membrane.
- Enzymes: Participate in reactions at the membrane surface.
- Linkers: Help stabilize the plasma membrane and attach cells together.
- Cell Identity Markers: Proteins unique to a person's cells; important in the immune system and in transplantation of tissue from one person to another.
The Nucleus
- Largest organelle of the cell.
- Surrounded by a nuclear membrane
- Contains:
- Chromosomes: Units of heredity; govern all cellular activity.
- Nucleolus: Assembles ribosomes.
Cytoplasm
- Material between the nuclear membrane and plasma membrane.
- Includes:
- Cytosol: Fluid portion of cytoplasm.
- Organelles: Specialized structures that perform different cell functions.
Surface Projections
- Structures that extend from the cell, such as:
- Cilia: Short, hairlike projections that move fluids around cells.
- Flagellum: Long, whiplike extension from the cell that moves the cell (e.g., in spermatozoa).
Organelles
Table 3-2: Overview of Cell Parts and Functions
- Plasma Membrane: Outer layer of the cell; composed mainly of lipids and proteins.
- Microvilli: Short extensions of the plasma membrane that absorb materials into the cell.
- Nucleus: Contains the chromosomes, directing all cellular activities.
- Nucleolus: Makes ribosomes.
- Cytoplasm: Site of many cellular activities.
- Cytosol: Colloid filling the cell; contains water, enzymes, nutrients, and other substances.
- Endoplasmic Reticulum (ER): Network of membranes within the cytoplasm.
- Rough ER: Has ribosomes attached; modifies, folds, and sorts proteins.
- Smooth ER: Participants in lipid synthesis.
- Ribosomes: Comprised of RNA and protein; manufacture proteins.
- Golgi Apparatus: Further modifies proteins and prepares them for transport.
- Mitochondria: Convert energy from nutrients into ATP.
- Lysosomes: Digest substances within the cell.
- Peroxisomes: Break down harmful substances.
- Proteasomes: Destroy improperly synthesized proteins.
- Vesicles: Store and move materials into or out of the cell.
- Centrioles: Help separate chromosomes during cell division.
Cellular Diversity
- Cell shape is related to cell function:
- A neuron’s long fibers transmit electric energy throughout the nervous system.
- Small, round red blood cells slide through tiny blood vessels.
- Cell organelle number is related to cell function:
- Lipid-producing cells have abundant smooth ER.
- Metabolically active cells have many mitochondria for ATP production.
Movement of Substances Across the Plasma Membrane
Summary of Membrane Transport
- Passive Transport (does not require chemical energy):
- Diffusion: Random movement of particles down the concentration gradient.
- Osmosis: Movement of water through a semipermeable membrane.
- Filtration: Movement of materials through a membrane down a pressure gradient.
- Active Transport (requires chemical energy):
- Active Transport (pumps): Movement of materials through the plasma membrane against the concentration gradient using transporters.
- Vesicular Transport: Movement of large amounts of material through the plasma membrane using vesicles (includes endocytosis and exocytosis).
Osmosis and Tonicity
Table 3-3: Solutions and Their Effects on Cells
- Isotonic: Cells remain unchanged in equilibrium with their environment (e.g., 0.9% salt or 5% glucose).
- Hypotonic: Cells take in water, swell, and may burst (e.g., <0.9% salt or 5% glucose).
- Hypertonic: Cells lose water and shrink, undergoing crenation (e.g., >0.9% salt or 5% glucose).
Active Transport
- Active transport uses chemical energy from ATP to drive movement against the gradient.
Endocytosis
- Engulfs materials into the cell.
Exocytosis
- Releases materials from the cell; the vesicle fuses with the plasma membrane.
Protein Synthesis
Overview
- Proteins: Perform structural and functional roles in a cell.
- DNA: Directs protein synthesis organized into genes and chromosomes.
- RNA: Participates in protein synthesis but is not part of chromosomes.
Comparison of DNA and RNA
Table 3-5: Comparison of DNA and RNA
| Feature | DNA | RNA |
|---|---|---|
| Location | Almost entirely in the nucleus | Almost entirely in the cytoplasm |
| Composition | Nucleotides (A, G, C, T) | Nucleotides (A, G, C, U) |
| Structure | Double-stranded helix | Single strand |
| Function | Codes for proteins | Assists in protein synthesis (mRNA, rRNA, tRNA) |
Transcription and Translation
- Transcription: Occurs in the nucleus, where DNA is transcribed into mRNA.
- Translation: Occurs in the cytoplasm, where mRNA is translated into proteins at ribosomes.
Cell Division
Mitosis and Meiosis
- Mitosis: Produces somatic cells (2n) and results in two identical daughter cells.
- Meiosis: Produces gametes (n) and reduces chromosome number by half.
Stages of Mitosis
- Prophase: DNA strands coil into chromosomes; nucleolus and nuclear membrane disappear; centrioles move to opposite poles.
- Metaphase: Chromosomes line up across the center of the cell; attach to spindle fibers.
- Anaphase: Centromeres split; identical chromosomes move to opposite poles.
- Telophase: Chromosomes reach poles; nuclear membrane re-forms; plasma membrane pinches off to create two daughter cells.
Cancer
Cellular Changes Leading to Cancer
- Genetic mutations may cause uncontrolled cell division, leading cells to spread (metastasize) and form tumors.
Cancer Risk Factors
- Heredity, Chemicals, Radiation, Obesity, Physical inactivity, Poor nutrition, Infectious agents.
Case Study: Cystic Fibrosis
- Cystic fibrosis is an inherited disease where a defective gene disrupts chloride channel protein synthesis, affecting osmosis and leading to thick mucus in lungs and pancreas.
Word Anatomy: Building Words Related to Cells
- Cyt/o (cell), micr/o (small), bi- (two), chrom/o (color), end/o (in, within), hem/o (blood), hyper- (over), hypo- (below), iso- (same), phag/o (to eat), ex/o (outside).
Final Thoughts
The importance of understanding cellular structure and function is pivotal for comprehending how cells maintain homeostasis, undergo division, and respond to their environment. This knowledge lays a foundation for exploring more complex biological and medical concepts.