3.2 Cells Flashcards
What is the cell surface membrane?
*double layer of phospholipids + larger proteins within bilayer
•controls movement in and out of cell
What is the structure of the nucleus?
•nuclear envelope= in + out
•nuclear pores= pass MRNA out
•chromosomes
•nucleolus
What is the function of the nucleolus?
Site of rRNA production, making ribosomes
What is the function of the nucleus?
•DNA replication
•transcription (mRna)
•genetic code for each cell
What is the structure of mitochondria?
•double membrane:
Inner is cristae which +SA for enzymes
•fluid centre is matrix
•loop of mitochondrial DNA: codes for enzymes for respiration
What is the function of mitochondria?
aerobic respiration to release ATP energy
What is chloroplast?
(Site of photosynthesis)
•double membrane
•thylakoids (stacks of flattened discs) with chlorophyll for light dependent reaction
•fluid stroma-enzymes for light independent reaction
What is the structure of the Golgi body?
•folded membrane stacked= cisternae
•vesicles pinch off from cisternae
What is a golgi vesicle?
Lipids + proteins are packed in special membrane bound parcels and transported
What is the function of the Golgi body?
•+ carb to protein= glycoprotein
•form lysosomes
•modify + pack proteins and lipids in vesicles
What are lysosomes?
*bags of digestive enzymes (hydrolytic enzymes)
•hydrolyses pathogens in phagocytosis
•breaks down dead cells (autolysis)
•exocytosis: release enzymes to outside to destroy material
•digest worn out organelles to reuse materials
What are ribosomes?
*subunits= rRNA + protein
80S = eukaryotic
70S = pro
Not membrane bound
•site of protein synthesis
What is the structure of endoplasmic reticulum?
•rough+smooth ER have folded membranes (cisternae)
•rough has ribosomes on cisternae
What does the rough endoplasmic reticulum do?
Modifies and transports proteins and glycoproteins
What does the smooth endoplasmic reticulum do?
Synthesis + storage of lipids, carbs, cholesterol and steroid hormones
What is the cell wall for plants and fungi?
(Provides structural strength)
Plants: micro fibrils of cellulose polymer
Fungi: chitin (N-containing polysaccharide)
What is the structure of the permanent vacuole?
•filled with fluid surrounded by single membrane (tonoplast)
•solution of mineral salts, sugars and amino acids, waste and pigments
What is the function of the vacuole?
•turgid: support
•temporary store of amino acids and sugars (food)
•pigment colours petals to attract pollination
•absorbs and hydrolyses potentially harmful substances
Why are prokaryotic cells different to eukaryotic cells?
•cytoplasm lacks membrane bound organelles
•smaller ribosomes (70S)
•single circular DNA free in cytoplasm
•DNA not associated with proteins
•cell wall that contains murein (glycoprotein)
+:
•plasmids
•capsule surrounds cell
•flagella
What is a virus and it’s structure?
(Acellular (no cells) and non-living)
•genetic material: RNA or DNA
•protein capsid
•attachment proteins identify + attach to host cells
•some have lipid envelope
How do viruses invade + hijack host cells?
1)attachment proteins bind to host cells receptor
2) DNA or RNA injected into host cell
3)host cell divides as normal + virus is replicated
What is magnification?
How much larger the image size is compared to actual size
What is resolution?
The smallest distance between 2 entities that can still be seen as separate entities
How do you use an optical (light) microscope? + Advantages
Beam of light is condensed using lens to form an image.
•alive + dead cells viewed
•easy sample preparation (no damage)
•cheaper and portable
Why does a light microscope have a lower resolution?
Longer wavelength of light
Why does TEM have the highest resolution?
Beam of e- have a much shorter wavelength
How is a transmission EM used?
•Beam of e-pass though very thin sample in vacuum.
•Focused using an electromagnet.
•absorbs e- = darker
Shows a detailed internal structure of organelles
How is a scanning EM used?
•e- beamed at surface
•e- knocked off sample + scattered= collected and amplified
3D outside surface structure
What are the disadvantages of an electron microscope?
•expensive
•complex sample preparation where it can alter and damage cells (artefacts)
•dead only = vacuum as e- absorbed so won’t reach specimen
•only black and white
How is an eyepiece graticule set up?
Eyepiece graticole is calibrated using a stage micrometer
How is ultracentrifugation carried out?
1) cells homogenised (broken up) in a cold, isotonic + buffered solution
2) homogenised mixture filtered to remove cell debris+unbroken cells
3) filtrate is put in centrifuge at low speed
4) densest organelle form pellets
5)supernatant spun at higher speed for more pellets
What is the order of collected pellets in a centrifuge? (Densest to least)
1) nuclei
2) i. chloroplast
2) ii. mitochondria
3) ER
4) ribosomes
Why must the homogenised mix be in a cold solution?
Reduces hydrolytic enzyme activity so organelles won’t be digested
Why must the homogenised mix be in an isotonic solution?
No osmosis in or out so the organelles won’t burst nor shrink
Why must the homogenised mix be in a buffered solution?
To keep Ph constant so organelles proteins + enzymes won’t be denatured
What is a cell membrane?
•phospholipid bilayer:
Hydrophobic tails face inwards
Hydrophilic head faces outwards
•partially permeable: allows any lipid soluble substances + very small substances e.g CO2
Why is a cell membrane described as a fluid mosaic?
• phospholipid molecules constantly moving
• composed of different molecules arranged as mosaic e.g proteins, cholesterol
What is the function of cholesterol in the cell membrane?
•Restricts movement of phospholipids = less fluid + more rigid
This helps to maintain shape of animal cells
What are extrinsic proteins used for? ( + e.g with use )
•Mechanical support
•glycoproteins + glycolipids which are used for cell recognition/signalling such as receptors
What are integral/intrinsic proteins used for and e.g?
•transport molecules across membrane
•channel and carrier proteins
How do channel proteins function?
Form tubes that fill with water to allow water soluble ions through membrane by facilitated diffusion
•selective as it opens only in presence of certain ions
How do carrier proteins function?
Bind to larger molecules like glucose and amino acids and will change shape to transport to other side
How is a temporary mount of tissue prepared for optical microscope?
1.Obtain thin tissue
2.place tissue in a drop of water
3.stain tissue on slide
4.add coverslip using mounted needle to avoid air bubbles
What is facilitated diffusion and what does it recquire?
Large, polar molecules can diffuse down the concentration gradient via channel and carrier proteins. It is a passive process
What is diffusion and what can move into membrane by diffusion?
1)Net movement of particles down a concentration gradient until equilibrium is reached. It is a passive process.
2)lipid soluble and small substances can move in
What is osmosis?
Movement of water form area of high to low water potential across partially permeable membrane. From a less negative to a more negative water potential
What is water potential and what does a lower pressure (kPa) for water potential mean?
1) pressure created by water molecules (KPa)
2)It has less water and is more concentrated with solutes
3) water= 0KPa and more concentrated become more negative
What is active transport and how does it work?
•Movement of polar/charged molecules against concentration gradient using ATP energy and a carrier protein
1)molecule binds to complimentary shape on protein
2) ATP bind to protein, hydrolysed to ADP +Pi
3)attached Pi causes protein to change shape + release molecule inside
4) when Pi is released carrier protein reverts to original shape
What is a co-transporter and how does it function?
•type of carrier protein
•it will bind to 2 molecules at a time
•conc. gradient of one is used to move another against its conc. gradient
How does the co-transport of glucose and sodium ions in the ileum work?
1.Na+ actively transported out of epithelial cell into blood by Na-K pump= lower conc. of Na+ in epithelium than ileum lumen (conc. gradient made)
2.Na+ can move down conc. in ileum to epithelium using co-transport protein.
- Glucose or AA will also bind to con-transport protein and move down
conc. gradient to epithelium
4.glucose and AA can move down conc. gradient from epithelium to blood by facilitated diffusion
What affects rate of active transport?
•speed of individual carrier proteins
•no. of carrier proteins
• rate of respiration= ATP
What affects the permeability of a membrane?
• temperature: high will denature membrane protein/increases fluidity of phospholipid bilayer/damage membrane
•Ph: changes tertiary structure membrane
•solvent: May dissolve membrane
How is a colorimeter used?
1) select colorimeter filter with complimentary colour
2)use distilled water to set it to 0
3) measure absorbance or % transmission of solution
4) high absorbance/ low transmission = more pigment in solution
What affects diffusion rate?
• concentration gradient
• surface area
• temperature
• diffusion distance
• size of molecule
What does a serial dilution do and why is it advantageous?
•Step by step dilution to produce different concentrations
•ad: makes very low concentration without measuring out small volumes, improving accuracy
What formulas are needed for dilution series calculations?
C1V1=C2V2
V2=V1 + volume of water to dilute
C1+V1: conc. and volumes of stock solution
C2+V2: conc. and volumes of solutions made
What are non specific responses to pathogens?
•skin: physical barrier + sebum
•tears: lysozymes
•Mucus traps dirt+microbes and cilia beats it away
•platelets produce clots
•phagocytes
•HCl in stomach
What are phagocytes?
Neutrophils (blood) attracted to chemicals by chemoattraction
Macrophages (tissues) recognise foreign atigen
(Bind, engulf and digest pathogens)
What is the process of phagocytosis?
1.attracted to chemicals/debris and recognise foreign antigens
2.Receptors bind + engulf pathogen by endocytosis = phagosome (enclosed vesicle)
3.lysosome fuse with phagosome = phagolysosome
4.lysosomes release hydrolytic enzymes= digest pathogens by hydrolysis
5.macrophage (only) will present antigen on cell surface membrane (APC)
Why is a thin sample needed for an optical microscope?
•let light through
•single layer of cell viewed
What happens to a cell when placed in a hypotonic solution?
It will gain water by osmosis down the water potential gradient, from a less negative water potential to a more negative water potential across a partially permeable membrane
*plant cell is turgid
*animal cell lysis
What stimulates the immune response?
•pathogens
•cells from other organisms/transplants
•abnormal cells/cancer
•toxins
What is the definition of an antigen?
Protein molecule present on cell surface membrane that stimulates an immune response by specific lymphocytes
What is the cell mediated response?
•specific T-H activated by APC
•T-H are cloned by mitosis and differentiate:
*cytotoxic T cells (T-C)
*T-memory cells
*activate B-lymphocytes
*stimulate phagocytosis
What is the humoral response?
•TH cells bind to antigen on APC
•specific T-H cells activate specific B-cells by releasing cytokines
•B cells clone by mitosis and differentiate (clonal selection)
•into plasma B cells and memory B cells
•plasma B cells release specific antibodies complementary to antigen causing agglutination
What do cytotoxic ‘killer’ T cells do?
They release perforin which makes holes on the cell surface membrane of APC and cause osmotic lysis
What is an antibody? (Structure + function)
•4 Polypetide chains joined by disulfide bridges (2 heavy/2 light)
•constant region: allows it to bind to WBC
•2 antigen binding sites to form antigen antibody complex (variable region)
•agglutination: clump up pathogens allowing quick + more phagocytosis
What is antigen variability?
DNA mutates in gene that codes for antigen. Antigen changes shape so previous memory cells are ineffective as no longer complementary to the new antigen (unrecognisable)
What is passive immunity?
1.antibody introduced from outside source
2.short term as antibodies broken down
3.fast acting (antidote)
E.g natural: breast milk
artificial: injection
What is active immunity?
1.involves memory cells
2.antibody made by plasma cells
3.long term immunity
4.can take time to develop
E.g natural: infection
artificial: vaccines
What is a vaccine?
•weak or dead pathogen (antigen)
•antigens on macrophages activate specific B cells to clone and differentiate into plasma + memory B cells
————————————————
•(during secondary immune response)memory B cells: divide rapidly into plasma cells to make large no. of antibodies rapidly = no symptoms
What is herd immunity?
Majority of people are immune so unvaccinated people are less likely to come in contact with infected people
What is the structure of HIV?
•RNA and reverse transcriptase in capsid
•viral envelope: made of membrane of host’s cell membrane
•glycoprotein: attach to TH cells receptors
How does HIV replicate in TH cells?
•HIV glycoprotein will bind to TH cells receptors
•HIV protein capsid fuses with TH cells membrane, allows RNA + enzymes to enter
•reverse transcriptase copies viral RNA into a DNA copy= moves to TH cell’s nucleus (DNA) (retrovirus)
•viral DNA transcribed into mRNA= viral proteins made to assemble new HIV
•released by “budding off”
When does HIV develop to AIDS?
AIDS is when HIV virus in TH cells interfere with normal functioning of immune system= left vulnerable to cancer and infections (immune system destroyed)
Why are antibiotics ineffective against viruses?
•Viruses don’t have cell walls that can be attacked by antibiotics
•no mechanism (protein synthesis/ respiration) that can be targeted
What are monoclonal antibodies used for and what are its ethical considerations?
•medical diagnosis e.g pregnancy/cancer
•target medicine to specific cell types by attaching drug to antibody
:
•deliberate induction e.g of cancer to animals
•testing/treatments have been dangerous
How does the ELISA test work and what does it tell you?
(If patient has antibody or antigens to specific disease)
1.testing wells lined with immobilised antibodies
2.sample added to well
3.wash to remove unbound antigens
4.enzyme-linked antibodies added bind to antigen
5.wash to remove unbound E-L antibodies
6.substrate added, changes colour if enzyme is present (antigen present)
What does the rate of colour change depend on in the ELISA test?
It is directly proportional to the amount of enzyme present (which is proportional to amount of antigen present)
What is the interphase part of the cell cycle?
(G1, S, G2)
•cell grows
•organelles and DNA replicated
•ATP content increases as energy needed for cell division
What are the steps in mitosis?
- Prophase: •chromosomes condense (short/fat), nuclear envelope breaks
•centrioles move to poles (spindle fibres)
2.Metaphase: •chromosomes move to middle
•spindle fibres attach to centromere and chromatid
3.Anaphase: •centromere divides, separates sister chromatids to poles (ATP used)
4.Telophase: •chromosomes longer and thinner, nuclear envelope reforms
•cytokinesis: division of cytoplasm
What is caused by uncontrolled cell division and how can it be stopped?
•cancers/tumours (caused by random mutations)
•drugs to stop DNA replication so cannot enter S phase
•radiation/drugs damage DNA and cell kills itself when detected
•prevent spindle fibre formation so inhibits metaphase / anaphase
What is the process of binary fission in prokaryotic cells?
•replication of circular DNA and plasmids
•(cell grows larger and circular DNA to poles)
•cytoplasm divides, murein cell wall forms= 2 daughter cells with circular DNA and variable no. of plasmids
Why do monoclonal antibodies bind to one specific antigen?
•produced from single clone of plasma B cells
•specific primary/tertiary structure (variable site)
•complementary shape to one antigen
Why are many fields of views used during experiments?
•ensures there’s a representative sample
Why do we push down hard in coverslip but not sideways in mitosis practical?
•to squash tissues to get a single layer of cells so light can pass through
•prevent rolling together of cells/avoid breaking chromosomes
How can a temporary mount be made to view with an optical microscope?
•obtain thin section (one layer of cells)
•place it on a drop of water on the slide
•stain with e.g iodine
•lower coverslip with a mounted needle
How can you use a temporary mount to determine the mean no. of specific organelles in the cells?
•select large no. of cells at random (more representative)
•count the total no. of the organelles in those cells
•divide the no. of the organelles by the no. of cells counted
What are the environmental conditions that can increase the growth rate of cells?
•increased oxygen/glucose to increase rate of respiration
•increased temperature to increase enzyme activity
•increased phosphate concentration so more ATP/DNA/RNA
Why does adding hypotonic solution in cells make the chromosomes easier to observe (mitosis)?
•Water moves into the cells by osmosis
•cells/cytoplasm gets bigger
What is microvilli?
Folded cell surface membrane
