3.2.1 Cell Structure Flashcards
What is a tissue?
A group of specialised cells
What is an organ?
A combination of different tissues that are co-ordinated to perform a variety of functions
What is an organ system?
Many organs working together to perform a function
Give an example of a organ system?
Digestive, respiratory or circulatory
A group of abnormal cells is….
A tumor
What is the adaptation of the sperm cell?
Organelles
Acrosome in head has digestive enzymes (break down egg)
Mid-piece packed with mitochondria to release energy for movement
Movement
Tail rotates so it can swim
What is the adaptation of the xylem and pholem?
XYLEM
No top/bottom wallas
Ligin = supports tubes
Cells w/o organelles so free movement of water
PHOLEM
Cells have few subcelluar structures
Made of living cells
Cells joined end to end = flow is easier
What are the adaptations of the root hair cell?
Increased surface area (uptake of H20 is greater)
Thinner walls = shorter diffusion pathway
Organelle
Mitochondria = active transport for mineral ions
Permanent vacuole = water potential is maintained
When do eukaryotes get specialised?
In multicelluar organisms
Eukaryotes have become specialised to specific functions
What is the adaption for the muscle cells?
Shape
Layers of protein filaments = cause contraction as they slide over each other
Organelles
High density of mitochondria = provide energy for contraction
What is the adaptation of the red blood cell?
Biconcave shape
No nucleus
= more space so more 02 can be transported
Give an example of a tissue?
Epithelial tissue, xylem and muscle
What are the adaptations of neurons?
Dendrites + axons → receive and transmit signals
Axons covered in fatty sheats
What is an Animal Cell made of?
Organelles (nucleus, endoplasmic reticulum, golgi body, lysosomes, mitochondria, ribosomes) – all have membrane except the ribosomes
Cytoplasm (site of chemical reaction)
Cell Membrane (holds cell contents together, controls what enters/leaves cell, cell signalling)
What two things can change with adaptation to a eukaryotic cell?
The shape of the cell
The organelles
Instead of a single membrane, the mitochondria is what?
Double membrane organelle
What is the cell surface membrane made out of?
Phospholipid bilayer
What does the cristae in the mitochondria provide?
A high surface area
What is the function of the chloroplasts?
The site of photosynthesis
What is the structure of the nucleus?
DNA (DNA wrapped in histones to make) chromatin Nuclear Envelope (double membrane) Nuclear pores Nucleolus Nucleoplasm
What are the functions of the nucleus?
Site of DNA replication and transcription
Contains the genetic code for a single cell
Describe the structure of the endoplasmic reticulum
Folded membranes
Fluid filled
RER AND SER
Function of the RER
Synthesize and transport proteins throughout the cell
Function of the SER
Synthesise, store and transport lipids and carbohydrates
What is the difference between the RER and SER?
RER has ribsomes on surfaces
SER has NO ribsomes
What is the function of the golgi apparatus?
Modify and package proteins
Packages into vesicles for transport
Digestive enzymes are placed into lysosomes
What is the function of the ribsomes?
Site of protein synthesis
Name all the organelles in a Eukaryotic Cell?
Cell surface membrane Nucleues Mitochondria Chlorplasts Golgi apparatus Lysosomes Ribosomes RER SER Cell wall Cell Vacoule
What is a plant cell made of?
Organelles w/ chloroplasts + vacuole
Cytoplasm
Cell membrane
Cell wall
What is the structure of the chloroplast?
Double membrane Contains thylakoids Thylakoids contain chlorophyll Stack of thylakoids is Granum Stroma is fluid surrounding
What is the role of the permanent vacuole?
Providing support = turgid
Stores sugars + amino acids
Pigments help attract pollinators
What is the function of the cell wall?
Provides stability
Prevents the bursting of the cell from osmosis pressure of water
What three things have a cell wall?
Fungi
Plants
Algae
What is the cell wall made of in plants?
Cellulose
What is the role of the cell surface membrane?
To control the movement of substances in and out of the cell
What are lysomes?
Relatively small organelles formed when the vesicles made by the golgi contain digestive enzymes
What are the four functions of the lysosomes?
Hydrolse phagocytotic cells
Break down dead cells
Break down old organelles
Release enzymes outside the cell to destory material around the cell (exocytosis)
What is the cell wall made of in fungi?
Chitin
What is the cell wall made of in Algae?
Cellulose or glycoprotiens
What organelles does a prokaryotic cell have?
Cell wall Capsule Cell surface membrane Cytoplasm Circular strand of DNA Plasmids Flagellum Ribsomes
What is the cell wall made of in Prokayotic cell?
Muerin (glycoprotien)
What is the role of plasmids?
Contains gene that aid survival of prokaryotes
Describe the structure of virueses
Nucleic acid (dna/rna)
a caspid
Attachment protien
Why are viruses described as acellular and non-living
- Acellular → not made of or able to be divided into cells
- Non-living → unable to exist/reproduce without a host cell
How does an optical microscope work?
Use light to form 2d images
What are limitations of light microscopes?
Low resolution so cant view smaller organisms
Only used on thin specimens
What are the advantages of optical microscope?
Can see living organisms
How does a Scanning electron microscope work?
Breams of electrons scan surface
Knocking off electrons from specimen
Gathered in a cathode ray tube to form a 3D image
What are the advantages of a SEM?
3D image
High resolution ( can see internal structures)
High magnification
Used on thick specimen
What are the disadvantages of the SEM?
Lower resolution than TEM
Cannot be used on living specimens
No colour images
What are the principles of TEM?
Beam of Electrons pass through specimen
Denser parts absorb more electrons
Denser parts are darker in appearance
Electrons have a short wavelength
What are the limitations/disadvantages of TEM?
Cannot be living
Specimen must be thin
2D image
What are the advantages of TEM?
High resolution; see internal structures
High magnification
Define ‘Magnification’
How much bigger the image of a sample is compared to the real size
What is the formula for magnification?
by Magnification =
size of image /size of the real object
Define ‘resolution’
How well distinguished an image is between 2 points;
Describe how you would measure size of an object viewed with an optical microscope
- Line up eyepiece graticule with stage
micrometer - Use stage micrometer to calculate the size
of divisions on eyepiece graticule at a
particular magnification - Take the micrometer away and use the
graticule to measure how many divisions
make up the object - Calculate the size of the object by multiplying the number of divisions by the size of divisions counted
- Recalibrate eyepiece graticule at different magnifications
In required practical 2, what are the limitations?
Squash and staining increase artefacts
An optical microscope has a low magnification power
Cut differently at root = inconsistent size of cells
How to convert μm → nm
x1000
How to convert μm → mm
divide by 1000
How were people testing for artefacts before modern technology?
Repeatedly prepared specimens in different ways
Compared each way, if one had a inconsistency when the others didn’t, most likely to be an artefact
How to convert cm → m
divide by 100
What is the formula for mitotic index?
undergoing mitosis/ total number of cells observed
What is the role of a stain in microscopy?
Used to colour components of the cell
What are artefacts?
things that arent actually part of the specimen
What is cell fractionation?
The process of separating cell organelles from each other
What is ultracentrifugation?
Process by which fragments in filtered homogenate are separated in a centrifuge
What are the stages in cell fractionation?
→ homogenisation
→ Filtration
→ Ultracentrifugation
Describe full process of Cell fractionation
Homogenise tissue in blender = break open cell
Place in a cold, isotonic, buffered solution
Reduction of enzyme activity
No water movement by osmosis/water potential
PH constant so enzymes dont nature
Filter homogenate to remove debris
Centrifuge homogenate = spun at low speed
Remove pellet of heavy organelle and spin supernatant at higher speed
Repeat at higher speeds until organelles separated out/or desired organelle
What is the supernatant?
Rest of organelles suspended after centrifuge
State and explain why we need the certain conditions in Homogenisation?
Ice cold = reduces enzyme activity
Isotonic solution = there is no osmosis pressure to do water potential ( no shrink/burst)
Buffered solution = PH at a constant level to prevent damage to protien structure
Breifly, describe stage of Homogensaiton
Cell in sample broken by blender
Must be under specific conditions: ice cold, isotonic and buffered solution
What is the order of organlles heaviest to lightest
Nuclei Chloroplasts Mitochondria Lysosomes Endoplasmic reticlum Ribosmes
(new cats make love even right?)
Which cells retain the ability to divide?
Eukaryotic Cells
What are the stages of Mitosis?
Prophase, Metaphase, Anaphase,Telophase and Cytokinesis
What occurs in Interphase?
S phase = DNA replicates semi-conservatively leading to two sister chromatids
G1 and G2 = no. of organelles and volume of cytoplasm increases; Protein synthesis and ATP content increases
Describe what occurs in Mitosis
Parent cell divisions
Two genetically identical daughter cells, containing identical/exact copies of DNA
PMAT stages
What occurs in Prophase?
Chromosomes condense Shorter and Thicker Two sister chromatids joined by a centromere Nuclear envelope breaks down Centrioles move to opposite poles Formation of Spindle fibers
What occurs in Metaphase?
Chromosomes align along equator
Spindle fibers attach to chromosomes by centromeres
What occurs in Anaphase?
Centromere divides
Spindle fibres contract
Pull sister chromatids to opposite poles of the cell
What occurs in Telophase?
Chromosomes decondesne
Longer and thinner
Nuclear envelope reforms = two nuclei
Spindle fibres and centrioles break down
What occurs in Cytokinesis?
The division of the cytoplasm producing two new cells
How many chromosomes do Human Diploid cells have?
46
Explain the importance of Mitosis
Growth of multicellular organisms by increasing cell number
Repairing damages tissues
Asexual Reproduction
How would recognise a cell in Interphase?
No chromosomes visible
How would recognise a cell in Prophase ?
Chromosomes visible but randomly arranged
How would recognise a cell in Metaphase?
Chromosomes lined up on equator
How would recognise a cell in Anaphase?
Chromatids being separated to opposite poles by spindles
How would recognise a cell in Telophase?
Chromosomes in two sets, one at each pole
What is a Malignant Tumor?
Cancer that spreads and affects other tissues/organs
What is a Benign Tumor?
Non-Cancerous
How do cancers start?
Changes occur in genes that control cell division - mutations
What are Carcinogens?
Agents that may cause Cancer
How do some cancer treatments work?
Disrupt cell cycle → Mitosis slows down → Tumour growth slows
In what two ways can you disrupt the cell cycle as a cancer treatment?
Prevent DNA replication → slows down mitosis
Disrupt spindle formation → chromosomes can’t attach to spindle by their centromere → sister chromatids can’t be pulled to opposite poles of cells = slower mitosis
What is the advantage and disadvantage of cancer treatments?
😊 - Drugs are more effective cancer cells
😔 - Disrupt cell cycle of normal cells too, especially rapidly dividing ones e.g. cells in hair follicles
How do Prokaryotic Cells replicate?
Binary Fission
Describe the process of Binary Fission
Circular DNA and Plasmids replicate
Cytoplasm expands as each DNA molecule moves to opposite poles of cell
Cytoplasm Divides
2 Daughter cells, each with single copy of dna and a variable number of plasmids
TRUE OR FALSE: “circular DNA replicates once, plasmids can be
replicated many times”
True
Why do viruses not undergo cell division?
They are non-living
Describe the process of viral replication
Attachment protein binds to complementary receptor protein on surface of host cell
Inject nucleic acid (DNA/RNA) into host cell
Infected host cell replicates the virus particles
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What is the Fluid-mosaic model of membrane structure?
- Molecules within membrane can move laterally (fluid)
- Mixture of phospholipids, proteins, glycoproteins and glycolipids
Describe the structure of the cell membrane
It has a Phospholipid Bilayer Hydrophilic heads and Hydrophobic tails Channel and Carrier Proteins (intrinsic) Glycolipids Glycoproteins Cholesterol
How does the Phospholipid help adapt the membrane?
Maintains a different environment on each side of the cell
Fluidity = can bend to take different shapes
How do surface proteins help adapt the membrane?
Cell recognition/Act as antigens/receptors
How does Cholesterol help adapt the membrane?
Regulates Fluidity/Increases stability
How does Cholesterol help adapt the membrane?
Regulates Fluidity/Increases stability
What is the main role of cholesterol in the cell membrane?
Make the membrane more rigid by restricting the lateral movement of molecules that make up the membrane
What is an example of cholesterol doing its role?
Binding to fatty acids causing them to pack more closely together
Describe Simple Diffusion
Net movement of small (non polar) lipid soluble molecules across a selectively permeable membrane down a concentration gradient
Passive
What factors affect Simple Diffusion
Surface area, concentration gradient and diffusion pathway distance
Describe Facilitated diffusion
Net movement of lager polar non-lipid soluble molecules aross a selectively permeable membrane down a concentration gradient
Passive
Through a channel protein/carrier protein
What is a Carrier protein?
Carrier proteins transport large molecules, the protein changes shape when molecule attaches
What is a channel protein?
Charged/Polar molecules through its pore
Describe Active Transport
Net movement of ions against a concentration gradient
Uses carrier proteins
Active
Uses energy to change shape of tertiary structure to push through protein
Describe Osmosis
Net movement of water molecules across a selectively permeable membrane down a water potential gradient
Passive
What factors affect Active transport?
PH Temp Speed of carrier protein No. of carrier proteins Rate of respiration (ATP)
What is water potential?
the likelihood (potential) of water molecules to diffuse out of or into a solution;
Describe co-transport (sodium and gluocse)
Movement of 2 different molecules
Sodium ions are actively transported out of cell into blood by Soidum potassium pump
Sodium ions and glucose move by facilitated diffusion into cell VIA co-transporter protein
Concentration gradient of glucose created (higher concentration in the cell than blood)
Concentration gradient causes glucose to move out of cell into the blood by facilitated diffusion through channel protein
How might cells be adapted for transport across their internal or external
membranes
- By an increase in surface area
- Increase in number of protein
channels / carriers
Define ‘Antigen’
Molecules which, when recognised as foreign by the immune system, can stimulate an immune response and lead to the production of antibodies (often on the cell surface membrane)
Why are antigens specific?
To allow the immune system to identify: Pathogens Cells from other organisms of the same species Abnormal Body cells Toxins released from bacteria
Describe the process of Phagocytosis
Phagocyte recognises foreign antigens on the pathogen and binds
Phagocyte engulfs the pathogen by surrounding it with its cytoplasm
Pathogen contained in vesicle/phagosome in the cytoplasm of phagocyte
Lysosome fuses with phagosome and releases lysozymes into vesicle/phagosome
These hydrolyse/digest the pathogen
Phagocyte becomes antigen-presenting and stimulates specific immune response
What is cell mediated immunity?
The type of response when T lymphocytes respond to antigens that are presented on a body cell
Describe the cellular response
T lymphocytes recognise APCs after phagocytosis
Specific T helper cells with receptors complementary to antigen binds
Becomes activated and divides rapidly by mitosis to form clones
What are clones formed in the cellular response used for?
Stimulate B cells for the humoral response
Stimulate cytotoxic T cells to kill infected cells
Stimulate phagocytes to engulf pathogens by Phagocytosis
Define a ‘Antibody’
A protein with specific binding sites produced by B cells in response to the presence of an appropriate antigen
What is Humoral Immunity/Response?
The type of response which involves B lymphocytes and antibodies
Describe what happens in the Humoral Response
Clonal Selection
Some become B plasma cells for the primary immune response - secrete large amounts of monoclonal antibody into blood
Some become B memory cells for the secondary immune response
Explain ‘Clonal Selection’
The receptor on helper t cell attaches to antigen
Activates t cell to divide rapidly
Forms genetically identical cells
These stimulate B-cells to divide and form clones
All produce the antibody that is specific to the foreign antigen
Describe the Primary response in terms of Immunity
Produces antibodies slower
Lower concentration of antibodies
T helpers need to activate B plasma cells to make the antibodies
Infected individual will express symptoms
Describe the Secondary response in terms of Immunity
Faster production of antibodies
Higher concentration
B and T memory cells are present
B memory cells undergo mitosis faster
What is the structure of an antibody?
Quaternary structure protein
What do we call it when a antibody binds specifically to antigens?
Antigen-antibody complex
Describe and explain how the structure of an antibody relates to its function
- Primary structure of protein = sequence of amino acids in a polypeptide chain
- Determines the folds in the secondary structure
- Determines the specific shape of the tertiary structure and position of hydrogen,
ionic and disulfide bonds - Quaternary structure is comprised of 4 polypeptide chains held by bonds
- Enables the specific shaped variable region (binding site) to form which is a
complementary shape to a specific antigen - Enables antigen-antibody complex to form
How do antibodies destroy a Pathogen?
Binds to two pathogens at binding site
Forms Antigen-antibody complex
Agglutination - antibodies clump pathogens together
Phagocytes bind to antibody + phagocytose many pathogens
What is a Vaccination
Injection of antigens from dead/weakened pathogens to induce artificial active immunity
How does a vaccine work?
Stimulates the formation of memory cells, forcing a faster and stronger secondary response
Describe the second exposure to a antigen after Vaccination against it
Faster secondary response Antibodies produced faster Higher concentration Destruction of pathogen (agglutination and phagocytosis) Immunity
What are the disadvantages of Vaccines?
Poor response
Antigenic Variation (mutate frequency is high so antigens change) causes it to be ineffective
Antigenic concealment
A vaccine that would eradicate a disease what should it not be?
Mutating
Having a life cycle w/ other organisms
Have symptoms that make it hard to diagnose or trace
What is Herd Immunity?
When a large proportion of the population has been vaccinated it makes it difficult for a pathogen to spread within that population.
How does Herd Immunity make it difficult to spread pathogens?
More people are immune so fewer people carry pathogen
Less likely that a non vaccinated individual will come in contact with an infected person and pass on the disease
What is active immunity?
Resistance to disease from an individual’s own immune system where an antigen induces plasma cells to make antibodies
What is passive immunity?
(Resistance to disease results from the) introduction of antibodies from another individual’s such as placenta/mother’s milk. Short lived
What are the differences between active and passive immunity?
Active Immunity Exposure to antigen Memory cells involved Antibody produced and secreted by B plasma cells Slower Long term immunity
Passive Immunity No exposure No memory cells Antibody introduced into body from another organism Fast acting Short term immunity
What are the ethical issues of vaccines?
Tested on animals before use on humans Tested on humans Vaccine may not work Expensive - less money spent of research and treatments of other diseases Can have side effects
What can antigenic variability be responsible for?
May experience a disease more than once
Vaccines against a disease may be hard
More frequent making of diseases
Explain the effect of antigen variability on disease
- Change in antigen shape (due to a genetic mutation)
- Not recognised by B memory cell → no plasma cells / antibodies
- Not immune
- Must re-undergo primary immune response → slower / releases lower concentration of
antibodies - Disease symptoms felt
What is a monoclonal antibody?
Antibody produced from a single group of genetically identical B cells/plasma cells
What are the use of monoclonal antibodies
Bind to specific complementary antigen
- Have a variable region with a specific tertiary structure/shape
- Only one complementary antigen will fit
Explain the replication of HIV in helper T cells
- HIV attachment protein attaches to a receptor on the helper T-cell membrane
- Virus lipid envelope fuses with cell surface membrane and capsid released into cell which uncoats, releasing RNA and reverse transcriptase into cytoplasm
- Viral DNA is made from viral RNA
- Reverse transcriptase produces a complementary viral DNA strand from viral RNA template
- Double stranded DNA is made from this (DNA polymerase) - Viral DNA integrated into host cell’s DNA (by enzyme integrase)
- Host cell enzymes used to make viral proteins from viral DNA (within human DNA) → viral proteins assembled with viral RNA to make a new virus
- New virus bud from cell (taking some of cell surface membrane as envelope)
How does HIV cause the symptoms of AIDS
Infects and kills helper T cells as it multiplies rapidly → cannot stimulate cytotoxic t cells, b cells and phagocytes
Immune system deteriorates = more likely to catch infections
Normal diseases can be more deadly
Why antibiotics are ineffective against viruses
Antibiotics can’t enter human cells - the virus exists in the host cell (acellular)
Viruses don’t have their own metabolic reactions
A resistant strain of bacteria via natural selection → reducing the effectiveness of antibiotics and waste of money
