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Cell Biology+ Flashcards

Introduction to Cells

Cell Theory

  • %%All living organisms are composed of one or more cells%%
  • %%Cells are the smallest units of life%%
  • %%All cells come from pre-existing cells%%

Atypical Cells

Striated Muscle Cell

  • composed of sarcomeres

  • each cell is multinucleated

  • the average muscle fibre is approximately 30 mm long (larger than a typical cell)

  • challenges the idea that a cell has one nucleus, as the striated muscle cell is comprised of multiple nuclei

Giant Algae: Acetabularia

  • genus of single-celled green algae of gigantic size, ranging from 0.5 to 10 cm in length

  • consists of the rhizoid (looks like small roots), the stalk and a top umbrella (made of branches that may fuse into a cap).

  • challenges the idea that cells must be simple in structure and small in size

Aseptate Fungal Hyphae

  • they are hyphae with many nuclei

  • they have NO septa

  • the result of this is shared cytoplasm and multiple nuclei

  • challenges the idea that a cell is a single unit (the fungal hyphae have many nuclei, are very large and possess a continuous, shared cytoplasm

Investigating Cells and Tissues with a Microscope

  • a typical cell ranges from 10 to 20 μm (micrometre) in diameter

Calculating Magnification

  • Commonly used units when measuring cells or cellular parts are:
    • {{1000 nm (nanometres) = 1 μm (micrometre){{
    • {{1000 μm (micrometres) = 1 mm (millimetre){{
  • <<magnification<< <<= size of drawing / actual size<<
  • <<size of specimen<< <<= field of view (FOV) / number of specimens<<
    • ensure that all measurements are given to the same units
  • <<total magnification<< <<= ocular lens magnification x objective lens magnification<<

Unicellular Organisms

  • {{Unicellular organisms carry out seven life functions:{{
    • metabolism
    • growth
    • response (to a stimulus)
    • homeostasis
    • nutrition
    • reproduction
    • excretion
  • homeostasis: %%the maintenance of a constant internal environment by regulating internal cell conditions.%%
  • metabolism:
    • %%the regular set of life-supporting chemical reactions that takes place within the cells of living organisms%%
    • it is the sum of all chemical changes that take place in a cell (synthesis of new molecules + breakdown of the removal of others)

Surface Area to Volume Ratio

  • %%the rate at which substances cross the cell membrane depends on their surface area%%
  • as a cell grows, the volume of the cell increases by a power of 3 (cubed), whereas the surface area of the cell increases by the power of 2 (squared). As such, the surface area to volume ratio decreases as the cell gets bigger.
  • as a cell increases in size, its surface area to volume ratio decreases
  • a large surface area to volume ratio allows for:
    • heat loss to occur faster
    • a larger and faster exchange of waste materials

Specialized Structures

  • villi and microvilli extend off the cell to increase surface area allowing for more efficient absorption
  • folds in the plasma membrane are found in the:
    • immune system
    • lungs
    • gastrointestinal tract
  • as a cell increases in size, its small surface area to volume ratio limits the rate of exchange of materials with its surroundings. A potential solution to this problem is developing projections from the cell membrane (microvilli) to increase its surface area

Multicellular Organisms

  • {{The evolutionary steps of multicellular organisms are as follows:{{
    • organisms grew larger as they were no longer limited by the size of one cell
    • limited by the size of one cell in such an organism were able to specialize through differentiation
    • multicellular organisms displayed emergent properties
  • genome: %%the complete set of genes, chromosomes or genetic material present in a cell or organism%%
  • differentiation: %%when an unspecialized stem cell changes and carries out a specific function in the body. cells differentiate to form different cell types due to the expression of different genes%%
  • according to emergent properties: a complex system possesses properties that its constituent parts do not have - the whole is more than the sum of its parts.

Cell Functions

  • Cell Membrane
    • semi-permeable membrane that protects the cell
    • lets things move in and out of the cell
    • location: around the cell
  • Nucleus
    • the control center of the cell
    • location: inside the cell, near the centre
  • Nucleolus
    • makes ribosomes
    • location: inside the nucleus
  • Nuclear Membrane
    • protects the nucleus
    • lets thing move in and out of the nucleus (pores)
    • location: around the nucleus
  • Mitochondria
    • produces energy (powerhouse of the cell)
    • location: in the cytoplasm
  • Golgi Bodies/Apparatus
    • packages and secretes waste
    • location: in cytoplasm
  • Endoplasmic Reticulum (E.R.)
    • transports materials and sends messages to all parts of the cell
    • There are 2 types of ER: rough (has ribosomes) and smooth
    • both have the same function
    • location: attaches from cell membrane to nuclear membrane
  • Ribosomes
    • makes proteins
    • location: in the cytoplasm or attached to the E.R.
  • Vacuole
    • stores food and water
    • plants have one big vacuole; animals have multiple
    • location: in cytoplasm
  • Lysosome
    • contains digestive enzymes
    • destroys bacteria, old cell parts
    • location: cytoplasm

Prokaryotic and Eukaryotic Cells

  • Procaryotic cells existed before eukaryotic cells
  • Pro=before
  • eu=true
  • eukaryotic cell: has a true nucleus
  • prokaryotic cells: have a nucleoid region, no nucleus

Prokaryotic Cells

  • one-celled organisms
  • prokaryotic cells go through asexual reproduction, called %%binary fission%%
    • fast, simple, requires few resources and less energy
    • good for rapid survivals of conditions that are harsh
    • short-term gain as a species
  • Process of binary fission
    • the chromosome is replicated semi-conservatively, beginning at the point of origin
    • beginning with the point of origin, the two copies of DNA move to opposite ends of the cell
    • the cell elongates (grows longer)
    • the plasma membrane grows inward and pinches off to form two separate but genetically identical cells
  • parts:
    • plasma membrane
    • cytoplasm
    • pili
    • flagella
    • 70S ribosomes
    • no organelles
    • few internal structures
    • unicellular or colonial
    • cell wall
    • cell membrane
    • circular chromosomes
    • no nuclear membrane. Has nucleoid region
    • plasmids

Eukaryotic Cells

  • contain organelles surrounded by membranes
  • can be unicellular or multicellular
  • eukaryotic cells have a compartmentalized cell structure, which refers to the formation of compartments within the cell by membrane-bound organelles.
  • parts
    • linear chromosomes
    • plasma membrane
    • cytoplasm
    • mitochondria
    • 80S ribosomes
    • nucleus
    • nucleolus
    • smooth and rough ER (endoplasmic reticulum) Golgi apparatus
    • vesicle
    • lysosomes
    • centrioles
    • vacuole
    • cell wall (plants and fungi)
    • the cell membrane (all)
    • chloroplast (only in plant cells)

Cell Membrane

  • the cell membrane is made of a phospholipid bilayer
  • proteins, lipids and carbohydrates (CHO) are scattered throughout two rows of phospholipid (PPL) molecules
  • proteins can be transmembrane/integral or peripheral
  • %%amphipathic: has both hydrophilic and hydrophobic, allowing for a natural arrangement into the bilayer.%%

Structure

  • hydrophilic heads face %%inside and outside of the membrane (the watery environments)%%

  • hydrophobic fatty acids %%face each other in the middle of the membrane%%

Functions of Cell Membrane

  • the function of the cell membrane is to control what enters and leaves the cell (the food goes in and waste goes out); acts as a barrier between the inside and outside of the cell
  • the cell membrane is semi-permeable
    • small, soluble lipids can pass through
    • water can pass through
    • large molecules CANNOT pass through (due to how tightly packed the PPLs are)
    • some molecules require energy
  • %%semi-permeable: only some molecules are allowed to pass freely%%

Fluid Mosaic Model

Phospholipid Bilayer

  • lipid bilayer: 2 layers of PPLs
  • phosphate head is polar (water-loving)
  • fatty acid tails non-polar (water-fearing)
  • proteins embedded in the membrane

Membrane Proteins

  • functions of membrane proteins:
    • receptor sites for hormones (hormone binding sites)
    • immobilize enzymes
    • cell adhesion - makes tight junctions between cells
    • cell-to-cell communication
    • transport of materials
    • passive transport
    • active transport

Types of Proteins:

  • Integral proteins

    • span across the membrane (transmembrane)
    • hydrophilic parts sticking out on either side of the membrane

  • Peripheral proteins

    • found on the inner or outer surface of the membrane
    • can be attached to integral protein

  • Glycoproteins

    • proteins with a carbohydrate (sugar) attached
    • usually involved in cell recognition, signalling or sites for hormone binding

  • Cholesterol

    • found only in animal cells
    • type of lipid-steroid
    • many are hydrophobic but has -OH (hydroxyl) group which makes that part of hydrophilic (to interact with (PPL heads)
    • involved in controlling the fluidity of the cellular membrane
    • disrupts the PPL molecules - makes the cellular membrane more fluid (not to crystallize)/ but not too fluid - rigid ring structure
    • reduces the permeability of hydrophilic molecule

Stem Cells

  • %%stem cell: an undifferentiated cell of a multicellular organism that can form more cells of the same type indefinitely, and from which certain other kinds of cells arise by differentiation%%
  • properties of stem cells:
    • self-renewal - the ability to divide and form new stem cells
    • potency - the ability to differentiate into different cells

Types of Stem Cells

Totipotent

  • %%each cell is able to develop into a new cell including extra-embryonic tissue%%
  • forms to make an entire organism
  • can be taken from early 1-3 days embryos
    • this is called the morula, which is the first cells that are formed following the fertilization of an egg cell
  • can differentiate into placental cells

Pluripotent

  • c%%ells that can form any type of cell (there are 220 cell types)%%
  • can be taken from the blastocyst (5 to 14 days)
  • can differentiate into all body cells; not able to make an entire organism

Multipotent

  • also called adult stem cells
  • appear in 14-day-old embryos and beyond
  • the stem cells will continue down certain lineages and cannot naturally turn back into pluripotent cells or switch lineages
  • can be taken from fetal tissue, cord blood and adult stem cells.
  • %%can%% %%only differentiate into some closely related types of body cells.%%
  • located in the "stem cell niche"

Characteristics of Stem Cells

  • unspecialized
  • divide rapidly
  • differentiate into several types of cells
  • have a large nucleus relative to the volume of cytoplasm
  • useful because they provide therapies for diseases and other health problems

Embryonic Stem Cells

  • nearly unlimited growth potential
  • is able to differentiate into any type of cell in the body
  • higher risk of becoming tumour cells than adult stem cells
  • lower chance of genetic damage due to the accumulation of mutations than with adult stem cells
  • often genetically different from an adult patent that is receiving the tissue
  • removing cells from an embryo kills it unless only one or two cells are taken.

Cord Blood Stem Cells

  • obtained and stored easily
  • commercial collection and storage services are already available
  • fully compatible with the tissues of the adult that grows from the baby, so no rejection problems occur
  • limited capacity to differentiate into different cell types - only naturally develop into blood cells, but research may lead to the production of other types
  • limited quantities of stem cells from one baby's cord
  • the umbilical cord is discarded whether or not stem cells are taken from it

Adult Stem Cells

  • difficult to obtain as there are very few of them and they are buried deep in tissues
  • less growth potential than embryonic stem cells
  • less chance of malignant tumours developing than from embryonic stem cells
  • limited capacity to differentiate into different cell types
  • fully compatible with the adult's tissues, so rejection problems do not occur
  • removal of stem cells does not kill the adult from which the cells are taken.

The Controversy of Stem Cells

  • embryonic stem cells are derived from
    • extra blastocysts that would otherwise be discarded after IVF
    • the blood from the umbilical cord
    • adult tissues such as bone marrow
  • extracting stem cells destroys the developing blastocyst (embryo)
  • can also be derived in a lab (induced pluripotent stem cells)
  • Therapeutic Uses of Stem Cells
    • Can be used in the treatment of leukemia and Stargardt's disease

Stages of Embryogenesis

  • cleavage
  • totipotent, 8-cell stage
  • pluripotent, turns into a blastocyst

Cellular Transport

Types of Cell Transport

Passive Transport

  • the cell does NOT use energy
  • simple diffusion
  • facilitated diffusion
  • osmosis
  • it is the movement of ions or molecules across a membrane from a region of a higher concentration to a region with a lower concentration
  • Simple Diffusion:
    • the random movement of particles from an area of high concentration to an area of low concentration
    • continues until all molecules are even spaces (equilibrium is reached)
    • note: molecules will still move around but stay spread out
  • Facilitated Diffusion
    • involves the transport of ions or molecules across a membrane through a membrane protein along the concentration gradient
    • from highly specific channels through the membrane
    • structure determines which particles can travel through
    • can be open or closed in response to signals from hormones, electric charge, pressure, light
    • requires channel proteins
  • Osmosis
    • diffusion of water through a selectively permeable membrane
    • water moves from high to low concentration
    • some cells have water channels called aquaporins
    • this increases the permeability of water in that cell
    • Hypotonic Solutions:
    • fluid surrounding the cell has a LOWER solute concentration than the cell's cytoplasm
    • water diffuses INTO the cell by osmosis (cell grows)
    • Isotonic Solutions:
    • fluid surrounding the cell has an EQUAL solute concentration as the cell's cytoplasm
    • water diffuses into and out of the cell by osmosis in equal amounts (the cell does not change size)
    • Hypertonic Solution:
    • fluid surrounding the cell has a HIGHER solute concentration than the cell's cytoplasm
    • water diffuses OUT of the cell through osmosis.

Active Transport

  • the cell uses ATP directly to move molecules or ions from one side of the membrane to the other
  • primary
  • secondary
  • involves concentration gradient
  • the cell uses energy (ATP)
  • actively moves molecules to where they are needed
  • movement from an area of low concentration to an area of high concentration
  • against the concentration gradient

Secondary Active Transport:

  • uses an electrochemical gradient as a source of energy to transport ions or molecules across a cell membrane
  • eg. ion pumps are carrier proteins that use ATP to pump ions across the membrane.
  • e.g. sodium/potassium pumps are important in nerve responses
  • concentration gradient→a difference in concentration between one side of the membrane and other
  • electrochemical gradient→the combination of a concentration gradient and an electric potential (voltage) across a membrane; stores potential energy that can be used by the cell
  • Sodium-potassium pump
    • maintaining an electrochemical gradient between the inside and outside of the cell; the inside is negatively charged
    • for every 3 sodium (Na+) ions that leaves, 2 potassium (K+) come in
    • the electrochemical gradient is used by nerve cells to relay signals

Membrane-Assisted Transport

  • the cell uses energy (from ATP)
  • endocytosis (phagocytosis, pinocytosis), exocytosis
    • this is done by vesicles
  • endocytosis
    • materials coming INTO the membrane
    • a cell engulfs material by folding the cell membrane around it, pinching it off to form a vesicle
    • e.g. antibodies from mom's milk, bacteria and viruses (immune system cells)
  • phagocytosis
    • cell-eating
    • endocytosis involving solid particles
  • pinocytosis
    • cell-drinking
    • endocytosis involving liquid particles
  • exocytosis
    • materials coming OUT of the membrane
    • vesicles fuse with the cell membrane and empty their contents into the extracellular environment
    • macromolecules and other large particles use this method to leave the cell
  • vesicles
    • a small sac of membrane
    • formed by "pinching" off of the plasma membrane or membrane-bound organelles (Golgi or ER)
    • moves things around the cell

Factors affecting diffusion

  • molecule size
  • molecule polarity
  • molecule or ion charge
  • temperature
  • pressure

Types of membrane proteins

  • channel proteins
  • carrier proteins

Carrier Proteins:

  • bind to specific molecules
  • transport them across the membrane and release them on the other side
  • changes shape
  • lower rates of diffusion than channel proteins
  • e.g. potassium channel in the axon (neurons)
    • K+ channels are voltage-gated in axon
    • when charges are more positive outside the axon, the channel is closed
    • when charges are more negative outside the axon, the channel opens temporarily allowing the k+ to leave through diffusion
  • in a hypotonic solution, water moves INTO the cell and the cell swells and bursts - the cell becomes turgid for plants and lysis for animals.
  • in a hypertonic solution, water moves OUT of the cell, and the cell shrinks and shrivels, this is called plasmolysis in plants and crenation in animal

Origin of Cells

Miller-Urey Experiment

  • simulated the conditions of early Earth's atmosphere - methane, hydrogen, ammonia gas
  • used electricity to simulate lightning and storms
  • Results:
    • a variety of small organic molecules were produced
    • e.g. amino acids (the building blocks of protein) and other carbon compounds

Conditions for Emergence of Life

  • Production of carbon compounds like sugars and amino acids (simple organic molecules)
  • Assembly of carbon compounds
    • inorganic chemicals, such as iron sulphide, supply energy which can be used to assemble carbon compounds into polymers
  • Formation of membranes
    • If amphipathic carbon compounds (like PPLs) were made - they can readily form vesicles that resemble the cell membrane. this creates a separate environment (allowing chemical reactions to occur) on the inside compared to the outside
  • Development of a mechanism for inheritance
    • early genetic material was not DNA but RNA, which has the ability to replicate by itself and can also be a catalyst.
    • since inheritance requires copying and passing genes onward and enzymatic reactions (catalyst), RNA was the best-suited molecule

Endosymbiosis

  • prokaryotes most likely gave rise to archaebacteria and eubacteria

Origin of Eukaryotic Cells

  • some prokaryotes lose their cell walls which allowed them to consume material through their cell membrane more easily.
  • this allowed cell membranes to fold inwards and evolved into membrane-bound organelles (which explains the appearance of mitochondria and chloroplasts)

Endosymbiotic Theory

  • early eukaryotic cells engulf aerobic heterotopic bacteria
  • bacteria were surrounded by a cell membrane and were not digested
  • they then entered a symbiotic relationship with the host cell and evolved into mitochondria
  • early eukaryotic cells engulf photosynthetic bacteria and then evolved into chloroplasts
  • Support for the endosymbiotic theory
    • mitochondria and chloroplasts are different from other organelles as:
    • they are surrounded by 2 membranes
    • have their own circular DNA
    • have 70s ribosomes
    • replicate their own DNA and undergo division independently (binary fission) from a host cell