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