Cells and Cell Membranes

Learning Objectives for Cells

  • Lesson 3.1: Cells and Movement of Substances Through Cell Membranes

    • Identify three major components of a cell and discuss the basic structure and function of the plasma membrane and cytoplasm.

    • List and briefly discuss the functions of the primary cellular organelles.

    • Discuss the basic structure and function of the nucleus.

    • Compare the major passive and active transport processes that act to move substances through cell membranes.

    • Discuss the relationship of cell transport to diseases.

Cell Size and Shape

  • Human cells vary considerably in size.

  • All human cells are microscopic.

  • Cells differ notably in shape, reflecting their unique functions.

Cell Composition

  • Cells contain:

    • Cytoplasm: A substance found only in cells.

    • Organelles: Specialized structures within the cytoplasm.

    • Plasma Membrane: The cell's interior is surrounded by a plasma membrane.

Parts of the Cell

Plasma Membrane

  • Forms the outer boundary of the cell.

  • Composed of a thin, two-layered membrane of phospholipids containing proteins.

  • Function: Selectively permeable, controlling substance movement in and out of the cell.

Structure of the Plasma Membrane

  • Components:

    • Phospholipid bilayer

    • Proteins

    • Cholesterol

    • Carbohydrate chains

Cytoplasm

  • Definition: Internal living material of cells.

  • Fills space between the plasma membrane and nucleus.

  • Contains organelles, which are numerous small structures vital for cell function.

Cell Structure

Nucleus

  • Surrounded by a nuclear envelope.

  • Contains:

    • Nucleolus

    • Nucleoplasm

    • Nuclear pores

  • Contains genetic material in the form of chromatin and chromosomes.

Organelles

Ribosomes

  • May attach to rough endoplasmic reticulum (ER) or lie free in cytoplasm.

  • Made of two tiny subunits of mostly ribosomal RNA.

  • Function: Manufacture enzymes and other protein compounds (often referred to as protein factories).

Endoplasmic Reticulum (ER)

  • Definition: A network of connecting sacs and canals that carry substances through the cytoplasm.

  • Types:

    • Rough ER: Collects, folds, and transports proteins made by ribosomes.

    • Smooth ER: Synthesizes chemicals; makes new membrane components.

Golgi Apparatus

  • Structure: A group of flattened sacs near the nucleus.

  • Function:

    • Collects chemicals into vesicles that move from the smooth ER to the plasma membrane.

    • Acts as the chemical processing and packaging center.

Golgi Apparatus: Cell's Protein Export System

  • Process Overview:

    • Ribosomes assemble proteins which are folded in the ER.

    • ER vesicles move to the Golgi apparatus for processing and packaging.

    • Proteins undergo chemical modifications as they move through Golgi chambers and get packaged into vesicles.

    • Secretory vesicles release their contents at the cell surface.

Mitochondria

  • Structure: Composed of inner and outer membranous sacs.

  • Function: Involved in energy-releasing chemical reactions and contain one DNA molecule.

Lysosomes

  • Structure: Membranous-walled organelles.

  • Function:

    • Contain digestive enzymes.

    • Participate in a protective function (eating microbes).

    • Previously thought to be responsible for apoptosis (programmed cell death).

Centrosome

  • Definition: A region of cytoplasm near the nucleus that serves as a microtubule-organizing center.

  • Contains centrioles, which are paired organelles lying at right angles to each other.

  • Function in cell reproduction.

Cell Extensions
Microvilli

  • Description: Small, hair likeextensions of the plasma membrane.

  • Function: Increase the absorptive surface area of the cell.

Cilia

  • Description: Fine, finger like extensions found on free or exposed surfaces of some cells.

  • Function: Capable of moving in unison in a wavelike fashion to move substances across the cell surface.

Flagella

  • Description: Single projections extending from cell surfaces.

  • Function: Much larger than cilia; in humans, they are exemplified by the tails of sperm cells.

Nucleus

  • Surrounded by a nuclear envelope made of two separate membranes with nuclear pores.

  • Contains:

    • Nucleolus: Dense region of nuclear material.

    • Chromatin: The structures that contain DNA, the genetic code responsible for protein synthesis, determining cell structure and function.

  • During cell division, DNA molecules become tightly coiled chromosomes, with each cell having 46 chromosomes in the nucleus.

Relationship of Cell Structure and Function

  • Each human cell has a designated function.

  • Specialized functions differ depending on the number and type of organelles present, affecting maintenance and regulation of life processes.

Movements of Substances: Cell Membranes

Passive transport processes

  • Definition: Do not require added energy.

  • Mechanics: Result in movement down a concentration gradient.

Diffusion

  • Definition: Substances scatter themselves evenly throughout an available space without requiring energy.

  • Mechanics: Movement occurs from high to low concentration.

  • Visual Representation: Illustration can depict a lump of sugar dissolving over time in water.

Osmosis and Dialysis

  • Definition: Specialized examples of diffusion across a selectively permeable membrane.

    • Osmosis: The diffusion of water when some solutes cannot cross the membrane.

    • Dialysis: The diffusion of solutes through a membrane.

Filtration

  • Definition: Movement of water and solutes caused by hydrostatic pressure on one side of the membrane.

  • Function: Responsible for urine formation.

Active Transport Processes

  • Definition: Occur only in living cells.

  • Mechanics: Movement of substances is against their concentration gradient; therefore, it requires energy from adenosine triphosphate (ATP).

Ion Pumps

  • Description: A protein complex in the cell membrane that uses energy from ATP to move substances across cell membranes.

    • Examples: Sodium-potassium pump, calcium pump.

    • Some pumps work with other carriers.

Sodium-Potassium Pump

  • Diagram Representation of how the sodium-potassium ATPase functions:

    • Highlights movement of Na+ and K+ ions across the cell membrane against their gradients using ATP.

Phagocytosis and Pinocytosis

  • Both processes are forms of active transport that require cellular energy.

    • Phagocytosis: Protective mechanism used to destroy bacteria.

    • Pinocytosis: Encompasses absorbing fluids or dissolved substances into cells.

Cell Transport and Disease

  • Cystic Fibrosis: Characterized by abnormally thick secretions in airways and digestive ducts due to failed Cl− (chloride ion) transport.

  • Cholera: Caused by a bacterial infection leading to Cl− and water leakage from intestinal cells, resulting in severe diarrhea and dehydration.

Learning Objectives for Cell Reproduction and Heredity

  • Lesson 3.2:

    • Compare and discuss DNA and RNA and their functions in protein synthesis.

    • Discuss the stages of mitotic cell division and explain the importance of healthy cellular reproduction.

    • Explain adaptability of cells to their environment through changes in growth and reproduction.

Cell Growth and Reproduction

  • Structure of DNA: Resembles a long, narrow ladder twisted into a double helix shape made of sugar (deoxyribose), bases, and phosphate units.

  • Bases: Nitrogen-containing chemicals include adenine, thymine, guanine, and cytosine.

Function of Genes

  • Each DNA molecule consists of genes.

  • Functionality:

    • Genes are copied as RNA transcripts (transcription).

    • Coding RNA dictates protein synthesis, determining cell structure.

    • Noncoding RNA supports or regulates structural and functional proteins of the cell.

DNA

  • Characteristics:

    • Complementary base pairing occurs with adenine-thymine and cytosine-guanine pairs on the DNA ladder.

    • A gene is a specific segment of base pairs within a chromosome.

  • Genetic Code: Sequence of base pairs governs heredity and controls enzyme production that facilitates reactions influencing cell structure and function.

RNA Molecules and Protein Synthesis

  • DNA is contained in the cell nucleus.

  • Protein synthesis occurs in the cytoplasm, thus requiring genetic information to pass from the nucleus via transcription and translation.

Protein Synthesis Overview

  • Begins with transcription where mRNA is formed along a gene sequence of DNA.

  • mRNA transports the genetic code to ribosomes where proteins are synthesized through translation.

  • Codon: Each series of three nucleotide bases represents a specific amino acid necessary for protein construction.

Protein Synthesis and Disease

  • Abnormal DNA that is inherited or damaged can lead to diseases.

  • Damaging factors include chemical, mechanical irritants, radiation, bacteria, and viruses.

Cell Life Cycle

  • Process: Reproduction involves both nuclear (mitosis) and cytoplasmic division.

  • Result: Two daughter cells.

  • Interphase: The period when the cell is not actively dividing.

  • DNA Replication: Process in which each half of a DNA molecule becomes a whole molecule identical to the original, preceding mitosis.

Cell Division Process

  • INTERPHASE:

    • Cell growth

    • Replication of chromosomes

    • Nucleolus visible

  • PROPHASE:

    • Chromatin organizes into chromosomes; centrioles move from the nucleus; spindle fibers appear.

  • METAPHASE:

    • Chromosomes align across the cell center; spindle fibers attach to chromatids.

  • ANAPHASE:

    • Centromeres break apart; chromatids move towards opposite ends; cleavage furrow forms.

  • TELOPHASE:

    • Cell division is completed; nuclei reappear in daughter cells; nuclear envelope reinstates; cytoplasm divides (cytokinesis).

Changes in Cell Growth

  • Hypertrophy: Increase in individual cell size leading to increased tissue size.

  • Atrophy: Decrease in individual cell size and subsequent tissue size reduction.

Changes in Cell Reproduction

  • Hyperplasia: Increase in cell reproduction leading to increased tissue size.

  • Anaplasia: Production of abnormal, undifferentiated cells.

Cancer

  • Overview: Abnormal growth of cells leading to formation of tumors and affected tissues, depicted through various tissue types and their abnormalities.

Questions?

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