Cell Biology Flashcards
Physiology
The study of the function of anatomical structures
Levels of Organisation: Chemical
Atoms combine to form molecules - determines function
Levels of Organisation: Cellular
Molecules interact to form organelles
Levels of Organisation: Tissue
A group of cells working together to perform one or more specific functions
Levels of Organisation: Organ
Organs consist of two or more tissues working in combination to perform several functions
Levels of Organisation: Organ System
Groups of organs interacting to perform a particular function forms an organ system
Levels of Organisation: Organism Level
All organ systems of the body must work together to maintain the life and health of the organism
Homeostasis
- Tendency toward internal balance
- All body systems working together to maintain a stable internal environment
Homeostatic Regulation
Adjustment of physiological systems to preserve homeostasis
Homeostatic Regulation: Autoregulation (Intrinsic)
Automatic response in a cell, tissue, or organ to some environmental change
Homeostatic Regulation: Extrinsic Regulation
Responses controlled by nervous and endocrine systems
Nervous System Characteristics
Rapid, short-term and very specific responses
Endocrine System Characteristics
Releases hormones (chemical messengers) which affect tissue and organs. Slow, long-term
Three components required for homeostatis
Receptor: Receives the stimulus
Control Centre: Processes the signal and sends instructions
Effector: Carries out instructions
Negative Feedback
- A stimulus produces a response that opposes or negates the original stimulus
- Provides long-term control over the body’s internal conditions and systems
- Corrective mechanism involving an action that directly opposes a variation from normal limits
Positive Feedback
- An initial stimulus produces a response that exaggerates or enhances the change in the original conditions creating a positive feedback loop
Cell Theory
- Cells are the building blocks of all plants and animals
- All cells come from the division of preexisting cells
- Cells are the smallest units that perform all vital physiological functions
- Each cell maintains homeostasis at the cellular level
Cytology
The study of cellular structure and function
Sex cells
Sperm and oocytes
Somatic cells
All other cells except sex cells
Plasma membrane
- Outer boundary of the cell
Functions of Plasma membrane
Physical Isolation: Separates inside of cell from the surrounding extracellular fluid
Regulation of Exchange: controls entry of ions and nutrients, elimination of wastes and the release of secretions
Sensitivity to Environment: First part of cell affected by changes in composition, concentration or pH of the extracellular fluid
Structural Support: Specialised connections between plasma membranes, or between membranes and extracellular materials, gives tissues stability
Membrane Lipids
- Phospholipid bilayer: hydrophilic tail, hydrophobic head
Membrane Proteins: Integral Proteins
Part of membrane structure, cannot be removed without damaging or destroying the membrane
Membrane Proteins: Peripheral proteins
Bound to the inner or outer surface of the membrane
Membrane Proteins; Functional Proteins: Anchoring Proteins
Attach plasma membrane to other structures and stabilise its position
Membrane Proteins; Functional Proteins: Recognition Proteins
Cells of the immune system recognise other cells as normal or abnormal based on the presence or absence of recognition proteins
Membrane Proteins; Functional Proteins: Enzymes
May be integral or peripheral proteins. Catalyse reactions in extracellular fluid or in the cytosol
Membrane Proteins; Functional Proteins: Receptor Proteins
Sensitive to the presence of ligands. Extracellular ligand will bind to complementary receptor which may change activity of cell
Membrane Proteins; Functional Proteins: Carrier Proteins
Bind solutes and transport them across cell membrane. May require ATP
Membrane Proteins; Functional Proteins: Channels
Some integral proteins contain a channel that forms a passageway completely across the plasma membrane
Membrane Carbohydrates
- Carbohydrate portion of molecules such as proteoglycans, glycoproteins and glycolipids, extend beyond the outer surface of membrane, forming a layer known as the glycocalyx
Glycocalyx Functions
- Lubrication and Protection
- Anchoring and locomotion
- Specificity in binding
- Recognition
Cytoplasm
- Material located between the plasma membrane and the nuclear membrane
- Contains cytosol and organelles
Cytosol
- Contains dissolved nutrients, ions, soluble and insoluble proteins, and waste products
Cytoskeleton
- Provides structural framework for a cell
- Movement of cellular structures and materials
Cytoskeleton: Microfilaments
Composed of actin. Anchor the cytoskeleton, determine consistency of the cytoplasm and actin will interact with myosin to produce movement of a portion of a cell
Cytoskeleton: Intermediate Filaments
Composed of keratin. Strengthen cell and help maintain its shape, stabilise the positions of organelles and stabilise the position of the cell
Cytoskeleton: Microtubules
Composed of tubulin. Form primary components of the cytoskeleton, disassembly of microtubules provide a mechanism for changing cell shape, can assist in moving vesicles or other organelles, form spindle apparatus in cell division and form structural components such as centrioles and cilia
Microvilli
- Finger-shaped projections of plasma membrane on their exposed surfaces
- Greatly increase the surface area of the cell exposed to the extracellular environment
Centrioles
- During cell division, centrioles form the spindle apparatus associated with the movement of DNA strands
- Intimately associated with the cytoskeleton
Cilia
- Long, slender extensions of the plasma membrane
- ‘Beat’ rhythmically to move fluids or secretions across cell surface
Ribosomes
Protein synthesis
Proteasomes
- Contain an assortment of protein-digesting (proteolytic) enzymes or proteases
- Responsible for removing and recycling damaged or denatured proteins, and for breaking down abnormal proteins
Endoplasmic Reticulum
- Network of intracellular membranes connected to the nuclear envelope
- Synthesis, storage, transport, detoxification
Nucleus
- Contains all the genetic material for the cell
- Surrounded by a nuclear envelope, communicates with the cytosol by the way of nuclear pores
Smooth endoplasmic reticulum
- No ribosomes associated
- Synthesis of the phospholipids and cholesterol needed for maintenance and growth of the plasma membrane, ER, nuclear membrane and golgi body in all cells
- Synthesis of steroid hormones
- Synthesis and storage of glycerides
- Synthesis and storage of glycogen in skeletal muscle and liver cells
Rough Endoplasmic Reticulum
- Newly synthesised proteins are chemically modified and packaged for export to their next destination, the golgi apparatus
Golgi apparatus
- Typically consists of five or six flattened membranous discs
- Functions:
- Modifies and packages secretions, such as hormones or enzymes, for release through exocytosis
- Renews or modifies the plasma membrane
- Packages special enzymes within vesicles for use in the cytoplasm
Lysosomes
- Are special vesicles that provide and isolated environment for potentially dangerous chemical reactions
- Produced at the golgi apparatus, contain digestive enzymes
- Degrades large molecules
- removal of pathogens
- Removal of damaged organelles
Lysosomal Storage Disorders
- Dysfunction of either lysosomal enzyme(s), a lysosomal protein involved in enzyme activation
- Accumulation of undigested material
- Chronic and progressive deterioration of cells, tissues and organs
Mitochondria
- Responsible for energy production
- Double membrane organelles, with inner membrane folds enclosing important metabolic enzymes
Peroxisomes
- Absorb and break down fatty acids and other organic compounds
Protein Synthesis: Transcription
DNA strands separate, the promoter has been exposed, RNA polymerase attaches to the template strand. Passes through the nuclear pore. Enters cytoplasm, carries information to ribosomes
Protein Synthesis: Translation
mRNA attaches to ribosome, tRNA brings specific amino acids to ribosome and anticodon on tRNA matches up with the complementary codon on the mRNA. tRNA molecules are released and when the polypeptide chain has been completed it breaks away from the ribosome into its final protein shape. Carries out function in cell
Gene
Section of DNA which has the instructions for one protein i.e. the sequence of amino acids
Codon
3 base code for an amino acid
Gene activation
- The gene is kept inactive by being tightly coiled and bound to histones.
- Gene activation requires the DNA to be uncoiled to expose the sites required to start the process of making protein e.g. transcription
- Every gene has a ‘start’ and ‘stop’
Protein folding diseases
- Caused by loss of protein function due to misfolding and degradation e.g. lysosomal storage disorders, cystic fibrosis
- Aggregation of misfolded protein outside the cell away from intracellular control mechanisms e.g. amyloidoses
- Parkinson’s diseases
- Alzheimers
The Cell life cycle
I: Interphase G1: Normal cell functions, plus growth, duplication of organelles and protein synthesis S: DNA Replication G2: Protein synthesis M: Cell division
DNA replication
DNA Strands unwind, and DNA polymerase begins attaching complementary DNA nucleotides along each strand. On one original strand, the complementary copy is produced as a continuous strand. Along the other original strand, the copy begins as a series of short segments spliced together by ligases. This process ultimately produces two identical copies of the original DNA molecule
Mitosis
- Divides duplicated DNA into two sets of chromosomes
- The DNA coils tightly into chromatids
- Chromatids connect at a centromere
- Protein complex around centromere is kinetochore
Prophase
Chromosomes are visible, centrioles move to opposite side of cell, nuclear envelope disappears, spindle fibres extend and attach to chromosomes
Metaphase
Chromosomes align themselves along the metaphase plate, equidistant from poles
Anaphase
Centromere split; two sister chromatids move to the opposite sides of cell
Telophase
Nuclear envelope forms, chromosomes change to chromatin, final location of nucleus at opposite ends of cell
Cytokinesis
Splitting of the cytoplasm with the formation of two identical cells
Cell death: Apoptosis
- Programmed cell death
- Activation of ‘suicide genes’
- DNA fragmentation
- Ingestion of dying cell by phagocytosis
Cell death: Necrosis
- Cell is injured
- Cellular contents flows into interstitial fluid
- Inflammatory response is initiated
Cell death: Cell ageing
- Involves telomeres
- As a cell divides it loses sections of the telomere
- Eventually, the cell stops dividing
Cell differentiation
The process of specialisation, results from the inactivation of particular genes in different cells, producing populations of cells with limited capabilities. Specialised cells form organised collections called tissues, each of which has certain functional roles
Cancer
Tumour results from abnormal cell division and growth
- Benign: Cells are contained, generally not life-threatening
- Malignant: Cells are no longer contained, can also travel to other organs and tissues
Diffusion
Process of molecules moving from a high concentration of that particle to a low concentration of that particle to create equilibrium; alcohols, fatty acids, steroids, gases
Facilitated Diffusion
- Substances can be passively transported across the membrane by carrier proteins
- Molecules must bind to a receptor site on carrier protein, shape of protein changes, moving the molecule across the plasma membrane and releasing it into the cytoplasm
- No ATP
- Molecules move from an area of high concentration to one of a lower concentration
- E.g. glucose and amino acids
Important factors for the rate of diffusion
- Distance
- Molecules size
- Temperature
- Gradient Size
- Electrical force
Osmosis
- Net movement of water molecules from a high concentration (low solute) to a low concentration (high solute)
Osmolarity/Osmotic concentration
- The total solute concentration in an aqueous solution
- Osmoles per litre (Osmol/L)
- Osmole is the number of moles of ions that contribute to a solution’s osmotic pressure
- Normal plasma (intracellular environment) approximates 285mosmol/L
Isotonic
Same concentration inside and outside the cell there is no net flow of water between the cell and solution
Hypotonic
Less salt concentration outside, water enters the cell which may eventually burst (lysis)
Hypertonic
High salt concentration outside, water will leave cell, which may lead to the cell shriveling (crenation)
Membrane Potential
- The transmembrane potential results from the unequal distribution of ions across the plasma membrane
- Transmembrane potential: The potential difference, measured in volts, between the two sides of a plasma membrane
- Resting potential: the transmembrane potential in an undisturbed cell
- In normal conditions: inside of plasma membrane is slightly negative with respect to the outside of the cell
- Slight excess of positive charges outside the cell
- Slight excess of negative charges and proteins inside the cell
Passive Transport
- Does not require energy
- Dependent on a concentration gradient
- Diffusion, osmosis, facilitated diffusion
Active Transport
- Requires energy
- Moving molecules against their concentration gradient from a low to a high
- Requires ATP
Sodium-potassium exchange pump
In the body
- Sodium ions are high in the extracellular fluid and lower in the cytoplasm
- Potassium ions are low in the extracellular fluid and high in the cytoplasm
- Ions can move down their gradients through leak channels
- 1 ATP molecule pumps 3 Na+ out and 2K+ in
What does homestasis within the cell depend on
The ejection of sodium ions and recapture of potassium ions
Secondary active transport
Moves a specific substrate down its gradient, 2 sodium ions bind, then glucose is transported into the cell followed by active transport of sodium ions out of the cell
Vesicular Transport: Endocytosis
Extracellular materials can be packaged in vesicles at the cell surface and imported into cell
Vesicular Transport: Receptor-Mediated Endocytosis
Produces vesicles that contain a specific target molecule in high concentrations
- Target molecules (ligands) bind to receptors
- Areas coated with ligands form deep pockets
- Pockets pinch off, forming endosomes (coated vesicles)
- Coated vesicles fuse with primary lysosomes to form secondary lysosomes
- Ligands are removed and absorbed in cytoplasm
- Lysosomal and endosomal membranes separate
- Endosome fuses with plasma membrane, receptors are again available for ligand binding
Vesicular Transport: Phagocytosis
Material is brought into the cell enclosed in a phagosome that is subsequently exposed to lysosomal enzymes
Vesicular Transport: Pinocytosis
Formation of endosomes filled with extracellular fluid
Vesicular Transport: Exocytosis
Fusion of vesicles containing fluids or solids (or both) with the plasma membrane and the release of contents to the outside
Phagocytosis and Gut diesease
- H. Pylori: bacterium that lives in the inner lining of the stomach
- Stimulates inflammatory immune response, contributing to the onset of gastritis, peptic ulcers and gastric cancer
- Engulfed by white blood cells called macrophages
- Resist digestion rather than fusing with a lysosome and being degraded
