2) Cells Flashcards
- Cell structure - Transport across cell membranes - Cell recognition and the immune system
what property of light limits the resolution of a light microscope?
light’s long wavelength
state the magnification equation
magnification = image size/object size
what is the definition of resolution?
the minimum distance apart that two objects can be distinguished as separate objects in an image
what are the two types of electron microscope?
transmission electron microscope (TEM)
scanning electron microscope (SEM)
how is the beam of electrons focused in an electron microscope?
by electromagnets
why do electron microscopes need to be in a vacuum?
so that the particles in air do not deflect the electrons out of the beam alignment
describe how a TEM works
A beam of electrons passes through a thin section of a specimen.
Areas that absorb the electrons appear darker on the electron micrograph produced.
describe how a SEM works
Beam of electrons passes across the surface of a specimen and scatters
The pattern of scattering builds a 3D image depending on the contours.
what are the main limitations of TEMs
system must be in a vacuum - specimen cannot be living
black and white image
specimen must be very thin for electrons to pass through
what are the main limitations of SEMs?
system must be in a vacuum - specimen cannot be living
black and white image
lower resolution than TEM
what is cell fractionation?
the process in which different parts and organelles of a cell are separated to be studies
what are the three main steps of cell fractionation?
homogenisation
filtration
ultracentrifugation
how can homogenisation be done?
grinding cells using a pestle and mortar, or in a blender
what is the purpose of homogenisation?
to break up the plasma membrane and release the organelles
describe the solution that the cells are homogenised in
ice-cold, isotonic, buffered
why must the solution be ice-cold?
to reduce enzyme activity that could break down the organelles
why must the solution be isotonic?
to prevent damage to the organelles through osmosis
why must the solution be pH buffered?
to prevent pH fluctuations
why is the solution filtered before ultracentrifugation?
to remove large debris
describe the process of ultracentrifugation
- homogenate (homogenised organelle solution) is spun at a low speed in a centrifuge
- heaviest organelles, the nuclei, are forced to the bottom forming a pellet
- fluid is removed leaving the nuclei pellet
- supernatant is spun again faster forming the next heaviest pellet - mitochondria
what are the defining features of a eukaryotic cell?
contain a nucleus and membrane bound organelles
describe the structure of the nucleus
Double membrane called the nuclear envelope containing nuclear pores.
Contains chromatin and a nucleolus.
Granular jelly like material called nucleoplasm makes up the bulk.
what is the purpose of the nuclear pores?
enable molecules to enter and leave the nucleus
what is the purpose of the nucleolus?
site of ribosome production
what is the substance that makes up the bulk of the nucleus?
nucleoplasm
what is the role of the RER?
folds and processes proteins made on the ribosomes
what is the role of the SER?
produces and processes lipids
what is the role of the golgi body?
processes and packages proteins and lipids
produces lysosomes
describe the structure of the mitochondria
oval shaped organelle bound by a double membrane
inner membrane folded to form cristae with matrix on the inside
what is the role of centrioles?
involved in producing spindle fibres for cell division
what is the role of ribosomes?
protein synthesis
what is role of lysosomes?
contain digestive enzymes so can digest molecules
what are prokaryotic cell walls made from?
murein (peptidoglycan)
what is the purpose of a prokaryotic cell’s capsule?
helps the cell retain moisture and adhere to surfaces
what is a plasmid?
circular ring of DNA
what is the role of a prokaryotic cell’s flagellum?
rotates to move the cell
what is the purpose of pili in a prokaryotic cell?
allow them to attach to other bacterial cells
what is the role of ribosomes in prokaryotic cells?
protein synthesis
what are mesosomes in prokayote?
infoldings of the inner membrane, containing enzymes for respiration
describe the structure of a virus
nucleic acid (either DNA or RNA) enclosed in a protein coat called the capsid, sometimes covered by a lipid layer called the envelope
what is the role of mitosis and the cell cycle?
to produce identical daughter cells for growth and asexual reproduction
what are the three stages of the cell cycle?
mitosis
interphase
cytokinesis
what are the four stages of mitosis?
prophase
metaphase
anaphase
telophase
what happens during interphase?
the cell grows and prepares to divide
chromosomes and some organelles are replicated
chromosomes begin to condense
what happens during cytokinesis?
the parent and replicated organelles move to opposite sides of the cell and the cytoplasm divides producing 2 daughter cells
mitosis is needed for what three reasons?
growth
repair
production
how is mitosis important for growth?
cells produced are identical so organisms can grow using mitosis
how is mitosis important for repair?
all cells produced are identical so organisms can replace dead tissues using mitosis
how is mitosis important for reproduction?
some single-celled organisms reproduce by dividing into two identical daughter cells by mitosis
what happens in prophase?
Chromosomes condense
Centrioles move to opposite ends of the cell, forming spindle fibres
Nuclear envelope breaks down and chromosomes are free in cytoplasm
what happens in metaphase?
Chromosomes line up along middle of the cell and become attached to the spindle by their centromere
what happens in anaphase?
Sister chromatids separate.
Chromatids are pulled to opposite poles of the spindle
what happens in telophase?
Chromatids decondense.
A nuclear envelope forms around each group of chromosomes so there are 2 nuclei.
Cytokinesis finishes
what is the name of the process by which prokaryotic cells divide?
binary fission
explain the steps of binary fission
Circular DNA replicates and attaches to cell membrane.
Plasmids replicate.
Cell membrane grows between the 2 DNA molecules and pinches inward, dividing cytoplasm.
New cell wall forms, dividing the original cell.
what genetic information do daughter cells created by binary fission have?
a single copy of circular DNA and a variable number of copies of the plasmids
why do virus not undergo cell division?
because they are non-living
how do viruses replicate?
inject their nucleic acids into another cell which then replicates the virus particles
what is the main function of the membrane?
controlling movement of substances in and out of the cell/organelle
describe the arrangement of phospholipids in the cell membrane bilayer
hydrophilic heads point outward (attracted to water on the outside of the cell)
hydrophobic tails point inwards (repelled by the water)
what kinds of molecules can pass through the phospholipid bilayer? what can’t?
lipid soluble molecules can pass through but water soluble cannot
what properties does the phospholipid bilayer give the cell membrane?
it is flexible and self-sealing
what is the difference between intrinsic and extrinsic proteins?
intrinsic - integrated fully throughout the membrane
extrinsic - on the surface
what 4 components are found embedded in the phospholipid bilayer?
proteins
cholesterol
glycolipids
glycoproteins
are carrier proteins intrinsic or extrinsic?
intrinsic
what is the purpose of proteins in the cell membrane?
aids movement across the membrane
provides mechanical support
act as receptors
what is the purpose of cholesterol in the cell membrane?
makes the membrane more rigid
reduces lateral movement of phospholipids
prevents water/dissolved ions leaking
how does cholesterol in the cell membrane prevent leakage of water and dissolved ions?
because it is hydrophobic
what are glycolipids?
carbohydrate bound to a lipid
what is the purpose of glycolipids in a cell membrane?
act as cell surface receptors and allow cells to adhere to one another, forming tissues
what is a glycoprotein?
carbohydrates attached to extrinsic proteins
what is the purpose of glycoproteins in a cell membrane?
act as cell surface receptors and neurotransmitters
allow cells to adhere to one another, forming tissues
what is diffusion?
passive movement of small, non-polar molecules down a concentration gradient through the phospholipid bilayer
what is facilitated diffusion?
movement of large, polar, charged molecules via a channel/carrier protein in the cell membrane down a concentration gradient
what is osmosis?
diffusion of water molecules down a water potential gradient through a partially permeable membrane
what is active transport?
movement of molecules through carrier proteins against a concentration gradient, using ATP
what is co-transport?
where two substances are both transported across a membrane simultaneously either in the same direction or opposite directions via a carrier protein
what four factors increase the rate of gas exchange by diffusion?
- increasing surface area of the exchange surface
- diffusion gradient becomes steeper
- temperature increases
- diffusion pathway decreases
what are the main differences between bacteria and viruses?
- bacterial are prokaryotic cells whereas viruses consist of nucleic acid in a protein coat
- bacteria do not require a host to survive, viruses do
- viruses are smaller than bacteria
- bacteria have cell wall, cell membrane and cytoplasm as well as organelles, e.g. ribosomes, whereas viruses do not
give three examples of physical barriers to infection
- skin (physical barrier consisting of keratin)
- stomach acid (HCl) (kills bacteria)
- gut and skin flora (natural beneficial bacteria compete with pathogens for food and space)
what allows the immune system to identify cells as self or non-self?
antigens on their surface
give four examples of non-specific immune responses
- inflammation
- lysozyme action
- interferons
- phagocytosis
explain inflammation as a non-specific immune response to infection
- histamine released by damaged tissues increase blood flow to affected area and increase permeability of blood vessels
- as a result, antibodies, WBCs, and plasma leak out into the infected tissues and destroy the pathogen
explain lysozyme action as a non-specific immune response to infection
lysozymes found in secretions such as tears and mucus kill bacterial cells by damaging their cell walls
explain interferons as a non-specific immune response to infection
interferons (protein released by body) prevent viruses spreading to uninfected cells by stopping protein synthesis in viruses
what are the two types of immune response?
specific and non-specific
where are B-cells produced? where do they mature?
- produced in bone marrow
- mature in bone marrow
where are T-cells produced? where do they mature?
- produced in the bone marrow
- mature in the thymus gland
which immune response are B cells involved in?
humoral response
which immune response are T-cells involved in?
cell mediated response
what are memory cells?
cells which replicate themselves when exposed to a pathogen and remain in the lymph nodes searching for the same antigen, resulting in much faster immune response if the person becomes infected with the same pathogen again
what is the role of plasma cells?
produce antibodies
what is the role of T-helper cells?
stimulate B cells and cytotoxic T cells to divide
what is the role of cytotoxic T-cells?
destroy pathogen-infected cells
what is an antigen?
protein that is recognised as non-self by the immune system and triggers an immune response
what does the presence of an antigen trigger?
the production of an antibody
what are the 2 kinds of immune response?
non-specific and specific
how are the effects of a specific immune response different to the effects of a non-specific?
specific responses are slower in action at first but can provide long-term immunity
where are lymphocytes produced?
by stem cells in the bone marrow
what are the 2 types of lymphocytes?
B-cells and T-cells
what has to happen for T-lymphocytes to respond to antigens?
antigens must be presented on a body cell
what are the four most common antigens?
- Pathogens
- Abnormal body cells (e.g. cancerous)
- Toxins
- cells from other individuals of the same species (e.g. transplanted)
Describe the stages of phagocytosis
- phagocyte recognises foreign antigens on a pathogen
- cytoplasm of the phagocyte engulfs the pathogen
- pathogen is how contained in a phagosome
- A lysosome fuses with the phagosome and releases lysozymes that break down the pathogen
- phagocyte presents the pathogen’s antigens on its surface to activate T- Cells
what are the first cells to respond to an immune system trigger?
phagocytes
where are phagocytes found?
in the blood and in tissues
what is the role of T- helper cells?
release chemical signals that activate phagocytes and cytotoxic T-cells
what do T-cells bind to? how?
they have receptors on their surface that bind to complementary antigens presented to it by phagocytes
what are B-cells covered with?
antibodies
what is formed when an antibody binds to an antigen?
antigen-antibody complex
why can each B-cell only bind to one specific antigen?
each B-cell has a different specific shaped antibody on its membrane so they can only bind to one specific antigen
