A DISORDER OF CELL DIVISON Mutations leading to cancer: switch on of 'divide' signal switch off of 'dont divide' signal loss of - correction mechanism on DNA copying escape mechanism from cell division limit of number of times a cell can divide control of keeping cells within tissue boundaries ability to evade body defence mehcanisms recuruit blood vessels to growing tumour migrate into blood stream of lymph vessels metastasis (development of a secondary tumour)

Cells and Organelles Flashcards by Trushna Damania

What constitutes a cell?

Cells( ORGANELLES AND MEMBRANE) => Tissues => Organs

Independent cells e.g. protozoa (occasionally form colonies)

Specialised cells can come together - advantage

Stem cells= divide to form clones; differentiation via switching on and off of particular genes triggered via cell signalling

Genes = production of protiens, enzymes, organelles, cell-cell contacts, secretion absorption.

Establishment of polarity

Cells respond to in-built development, external factors and epigenetics

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What are the scales of cells and molecules?

Average Cell: 25 micrometers

Nerve/muscle cell: 10cm

Globular protiens: nanometers

Virus: 20-30 nm

Metabolite e.g. ATP: Angström

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Identify and explain the role of organelles in a cell.

Nucleus = contains genetic material and site of transcription of RNA

Nucleolus = site of transcription of ribosomal RNA

Nuclear envelope = seperates nucleus from cytoplasm

Mitochondrion = different forms in different cell types, polymorhpic, site of aerobic respirations to synthesise ATP via oxidative phosphorylation

Rough Endoplasmic Reticulum = studded with ribosomes, for protein synthesis (extracellular or membrane proteins)

Smooth Endoplasmic Reticulum = involved in lipid synthesis

Ribosomes = involved in protein synthesis

Golgi Apparatus = controls traffic of protiens with in cells and between organelles.

Secretory Granule = vesicles required for exo/endocyotsis

Plasma Membrane = seperates cell from external environment

Cytoskeletal components = FILAMENTS; microtubules (tubulin), actin (actin) and intermediate (various proteins)

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What are the main types of molecules in a cell and their properties?

Solutes found in a cell:

soluble protiens

ions

sugars

nucleotides (ATP, cAMP, GTP)

amino acids

m/tRNA

lipids

peptides

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Differentiate between eukaryotic and prokaryotic cells.

Eukaryotic cells - mammalian cells CONTAINS MANY MEMBRANE BOUND ORGANELLES

Prokarytoic cells - bacterial cells NO MEMBRANE BOUND ORGANELLES

Additional components: photosynthetic pigments, flagella (locomotion) and pili (adhesion)

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Describe types of molecule/organelle/cell movement.

Molecule movement: simple diffusion

Organelle movement: REQUIRES ATP HYDROLYSIS movement through cytoskeleton via motor proteins

e.g. growth of cells, movement of cell membranes, cell divison

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What is cancer?

A DISORDER OF CELL DIVISON

Mutations leading to cancer:

switch on of ‘divide’ signal
switch off of ‘dont divide’ signal
loss of -
- correction mechanism on DNA copying
- escape mechanism from cell division
- limit of number of times a cell can divide
- control of keeping cells within tissue boundaries
ability to
- evade body defence mehcanisms
- recuruit blood vessels to growing tumour
- migrate into blood stream of lymph vessels
- metastasis (development of a secondary tumour)

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What are the main functions of blood?

Transport of molecules (CO₂, O_2,urea, hormones etc)

Heat distribution

Immunity (white blood cells)

Haemostasis (particularly role of platelets, preventing blood loss)

Homeostasis

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What are the major components of blood?

Erythrocytes

Leukocytes

Platelets

Plasma

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What is the structure, role and importance of haemoglobin?

Structure:

Quartenary structure (2 alpha and 2 beta chains) with a haem group (Fe²⁺) which can combine with one molecule of O₂ each. Oxidised form= Fe³⁺ (methaemoglobin- doesnt carry O₂)

Role:

Transport of O_{<strong>2</strong>}(lower affinity; 2^nd haem binds more easily than 1^st due to breaking of conformational shape of globin molecules= cooperative binding) to respiring cells and CO₂ to lungs to be excreted (greater affinity and forms carboxyhaemoglobin)

Importance:

Allows for aerobic respiration in cells.

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What are the essential features and functions of erythrocytes?

Features:

no organelles - only contains

biconcave disk - maximum surface area and flexible

blood group determined by molecules on surface

Functions:

respiratory transport of O₂as oxyhaemoglobin and CO₂ dissociates into bicarbonate ions (enzyme- carbonic anhydrase)

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Define anaemia

Low blood haemoglobin concentration

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Explain the life cycle of erythrocytes.

Only 120 day lifespan- then removed by macrophages

Immature erythrocytes- contain ribosomes = RETICULOCYTES (used as a diagnostic test e.g. chemotherapy or anaemic)

Production of erythrocytes = erythropoiesis stimulated by an increase in the hormone erythropoietin (released in low O₂ conditions) , and in men testosterone too. Cells in bone marrow differentiate into erythrocytes

Increase in RBCs ► Increase in blood Hb ► Increase in blood O₂

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What are the different types of anaemia?

MCV= Mean Cell Volume

Microcytic (small MCV) = failure of haemoglobin sythesis - Fe defincinency
- menstruation
- GIT lesions/ cancer
- parisitic infection
Normocytic (normal MCV)
- acute blood loss
Macrocytic (large MCV)
- failure of DNA synthesis and cell divison; reduced divison of progenitor cells- fewer but larger erythrocytes
- deficinecy
  - folic acid = (thymine sythesis) during pregnancy
  - vit B12 = (needed for folic acid action) autoimmune disease, diet e.g. vegetarian/vegan

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What are polymorphonuclear granulocytes?

Polymorphonuclear granulocytes:

NEUTROPHILS (phagocytic)
EOSINOPHILS (allergy)
BASOPHILS (production of histamine)

segmented nucleus
many cytoplasmic granules
adheres to blood vessels & migrates to tissue
engulf, kill and digest microorganisms
release of inflammatory mediators e.g. toxic O₂ products/ digestive enzymes/ vasodilators/ chemotaxins

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What are B-lymphocytes?

Matured in bone marrow
Humoral (anti-body mediated) immunity
Immunoglobins (antibodies) produced upon detection of a foreign antigen
IgM, IgG, IgA, IgD, IgE
Assistance in phagocytosis
- precipitation
- agglutination
- opsonisation
- neutralisation
Secondary response = greater, quicker, longer due to memory cells

What are T-lymphocytes?

Thymus dependent - migrate and mature in thymus to become immunologically competent (acquiring surfance antigen molecules)
Cellular immunity (cell-mediated response)
circulate- foreign antigen- blast transformation- progeny with receptors for antigen
Activated T-lymphocytes produce
- chemotaxins (attract macrophages)
- lymphotoxin (kills cells)
- interferon (kills viruses)

What are monocytes?

Appearance = large, single horse-shoe nucleus
Appear after granulocytes
Become macrophages in the tissue
Engluf microorganisms, tissue debris and dead polymorphs
Secrete inflammatory mediators and stimulate angiogenesis (vessel growth= repair)

What are the functions of platelets?

DESCRIPTION

Derived from megakaryoctes
2-3 micrometer in diameter
life span of 8-10 days
granules
many organelles but NO NUCLEUS

FUNCTION

express surface receptors for platelet activators (collagen- vessels and thrombin- coagulation cascade)
adhesion to exposed collagen (wound/ atherosclerosis)
release of granules ► platelet aggretion
produce thromboxane A₂via enzyme cycloxygenase - clot/thrombus formation
aspirin inhibits cycloxygenase (anti-platelet)
inhibition of platelet activation by prostacyclin and nitric oxide

What is the concept of the immune response?

Detect foreign antigen
Release of granulocytes
Release of T then B lymphocytes
Release of monocytes

What is the concept of passive immunity?

Immunity gained via acquiring antibodies without stimulating the immune response.

ARTIFICIAL: injection of antibodies

NATURAL: passed from mother to feotus

What are the major functions of plasma?

The fluid component of blood - acts as a carrier for cells, proteins and molecules

Nutrients = glucose, lipids and amino acids
Hormones = thyroxine, cortisol, erythropoietin
Proteins = fibrinogen (clotting), albumins and globulins (carrier molecules; hormones, bile salts, water, insoluble drugs)
Inorganic ions = Na⁺, K⁺, Ca²⁺, PO₄^3-, HCO₃^-
Products of metabolism = urea, lactic acid

Serum - plasma with proteins removed due to clotting

Explain the formation of phospholipid bilayers in an aqueous environment.

Phospholipids

hydrophilic head
hydrophobic tail

Tails pack together to avoid water. Either forms micelles (droplets) or a bilayer (liposomes)

Forms the limit of a cell and also surrounds intracellular compartments- organelles

What are the stuctural components in a phospholipid?

Phospholipids can be described as amphiphilic (contains both hydrophobic and hydrophilic)

PHOSPHATIDYLCHOLINE/ LECITHIN

Choline, phosphate and glycerol = phosphate head
Saturated/ unsaturated = fatty acid chain

Other consituents are phosphatidylethanolamine, phosphatidylserine and sphingomyelin

Unsaturated=kinky=sparse

Saturated=straight=close

What are the permeability properties of the phospholipid bilayer?

Selective permeability Permeable to: * small neutral molecules; water (osmosis), O_2, CO₂and other nutirents (perhaps via simple/facillitated diffusion) Impermeable to: * large, hydrohilic/ charged molecules * cations (K, Na, Ca) * anions (Cl, HCO3) * proteins/ RNA

What is simple diffusion?

Passive movement of molecules across a selectively permeable membrane going down a concentration gradient.

What is facilitated diffusion?

The movement of charged (hydrophilic) molecules down their concentration gradient via protein pores - provides shielding from hydrophobic core of phospholipid bilayer

What is active transport?

The movement of molecules across a selectively permeable membrane going against the concentration gradient May include the use of pumps/ transporters * symporters = molecules move in one direction * antiporters = molecules can move in opposite directions Others use vesicles = pinocyosis, phagocytosis, endocytosis, exocytosis

Explain the movement of Na⁺and K⁺ ions across the cell membrane?

Na⁺and K⁺ pump exchanges 2Na inside and 3K outside Energy gained from: phosphorylation of aspartyl residue and hydrolysis of aspartylphosopate Ionic gradient (less Na and more K on inside than outside) Charge gradient (more + charges outside so inside has a more negative potential) Membrane potential - 70mV; breif distruption can cause an ACTION POTENTIAL (only in nerves and muscle cells). Na enters causing depolarisation - K efflux helps to restore membrane potential.

Explain how amino acids and glucose enter a cell.

Symport transporter used Glucose is contransported with Na (facilitated diffusion) moves down concentration gradient into the cell

Explain briefly the mechanism of cell signalling.

Signals must cross membranes too: * lipid-soluble (steroid hormones) * via exocytosis (hormones) * trans-membrane receptors (gating ion channels/ receptor mediated signalling)

List the main types (with examples) of infectious agents which cause disease in humans

* Prokaryotes * Viruses = HIV, influenza * Bacteria = Shigella, Mycobacterium tuberculosis * Eukaryotes * Fungi = Candida albicans, Aspergillus fumigatus * Protozoa = Plasmodium, Leishmania * Helminth parasites (multicellular) = tapeworms, flukes

What are the key differences between prokaryotes and eukaryotes?

* Prokaryotes don't have an internal membrane * Prokaryotes tend to have a single chromosome * Prokaryotes have a cell wall made of peptidoglycan * Prokaryotes do not have a well defined cytoskeleton

What are the distinguishing features and replication mechanisms of infectious agents?

VIRUSES: obligate parasites, contain own genetic material but uses host cell to make proteins and to replicate, divides by budding BACTERIA: prokaryotes, divide by binary fission FUNGI: can occur as yeast(bud or divide ) /filaments( have cross walls), can cause cutaneous, mucosal and systemic mycoses PROTOZOA: usually have a complicated life cycle with two hosts, infection occurs via a vector or ingestion, replication occurs via binary fission or forming trophozites HELMINTH PARASITES: multi-cellular and visible to the naked eye, life cycle is outside human host with varying complexity