UNIT 2, Topic 2A & 2B - Cells Flashcards
Function of the cytoskeleton
Network of protein fibres - provides strength/ shape
What is the nucleolus?
(Concentrated area inside nucleus) Composed of protein and RNA, involved in ribosome production
Function of the vacuole
Vesicle that provides storage of water and other minerals (like cell sap, weak solution of sugars and salts dissolved) - surrounded by a membrane called tonoplast. Maintains cell’s pressure so to not wilt and be rigid.
- Also involved in isolation of unwanted chemicals
Function (and description) of the nucleus
Double membrane organelle as surrounded by a nuclear envelope, with nuclear pores. CONTAINS CHROMOSOMES (protein bound linear DNA held by histones). Controls cell activity and DNA that has instructions for protein synthesis. Pores allow substances to move into or out the cytoplasm, like RNA.
- CONTAINS CHROMATIN (mix of DNA and proteins that makes chromosomes)
What is a plasmodesma?
A structure in (plant) cell walls; a channel allows molecules and substances to move back and forth as needed. Additionally, they also create junctions from cell to cell,
allowing numerous cells to work together towards a common goal.
How is algae different to plant cells?
They can be unicellular (Chlorella) or multicellular (seaweed), plants tend to have many cells.
How do fungal cells differ to plant cells?
- dont photosynthesise or have chloroplasts
- cell walls made of chitin, not cellulose
Function of cell wall
Supports and prevents cell from changing shape (remains turgid)
Function of cell surface membrane
Regulates movement of substances in and out of cell. Has receptor molecules on it, allows to respond to chemicals like hormones.
What is the cell membrane made of?
Mainly lipids and proteins
Describe the structure of mitochondria and their related function
Double membrane, one is folded into structures called cristae. Inside this, there is the matrix WHICH contains enzymes involved in respiration.
- produce ATP from aerobic (cellular) resp. Usually a lot of them in active cells.
Describe the (ultra)structure of chloroplasts
Small flattened structure (see drawn notes). Double membrane. Thylakoid membranes stacked up to form grana. Thin, flat pieces of thylakoid membranes join the grana- these are called lamellae.
How structure of chloroplasts links to function
Where photosynth. happens.
Some of it happens in the grana or in stroma.
Golgi body and RER both process substances. What is the difference between them?
Golgi body processes and packages new LIPIDS and proteins. Rough ER processes and FOLDS only proteins.
Structure and function of golgi body?
Group of fluid filled, membrane bound flattened sacs.
- vesicles
Processes and packages new lipids and proteins. Makes lysosomes.
Structure and function of golgi vesicles
Small fluid filled sacs in cytoplasm, membrane bound, produced by golgi apparatus.
- STORES lipids and proteins made by the golgi apparatus and transports out cell via cell surface membrane (exocytosis).
Structure and function of ribosomes
Floats freely in cytoplasm, attached to RER. Made up of RNA and protein. NO MEMBRANE.
The site where protein synthesis
Structure and function of lysosomes
Round organelle with membrane. Type of golgi vesicle, no clear structure.
Contains digestive enzymes: lysosomes. Kept separate from cytoplasm by membrane, and can be used to digest invading cells or break down worn out components of the cell.
- used in phagocytosis.
3 L’s of light (optical) microscopes
Light microscope
Longer wavelength (of light)
Lower resolution and magnification
- electron microscope has higher resolution due to the electrons being fired having a shorter wavelength.
Disadvantage of electron microscopes and light microscopes
Electron: specimen must be dead, electrons may damage sample, black and white
Light: lower resolution so can’t see organelles in detail
Describe how to prepare a microscope slide for light microscope (any specimen)
- explain why each step must be done.
- A temporary/ wet mount can first be produced; pipette a small drop of water onto the slide
- sample held in place by surface tension and also won’t dry out. - Using tweezers, place a thin section of specimen (one cell layer thick so light can pass through) onto droplet
- Add a drop of stain - stains cling to organelles and highlights them
- Slowly lower cover slip at an angle to reduce appearance of bubbles
What is a temporary (wet) mount?
- dry mounts also exist
Where a specimen is suspended in a drop of liquid (oil or water) on a microscope slide (either glass or plastic)
- they’re temporary and can’t be stored fo very long, good for looking at organisms that live in water
When preparing a microscope slide for an optical microscope, suggest what stain could be used for animal cells and plant cells
Animal: eosin solution/ stain
Plant: iodine solution
- Consider if the stains may be hazardous
2 types of electron microscopes
SEM (scanning) and TEM (transmission)
What is a plasma membrane and why is it said to act as a partially permeable barrier?
The collective name given to the membrane surrounding cells AND organelles (cell-surface membrane is just for cells).
It is selective with the substances that can move in and out
Why may a partially permeable barrier be needed (2)
- Contain and isolate enzymes (e.g. respiratory)
- Allow molecules needed (glucose and oxygen) in and out (h²o, co²)
What are the components of the cell surface membrane
Phospholipid bilayer, glycoproteins/lipids, cholesterol, channel/carrier proteins (even receptor proteins)
Which organelles transports substances in/out of organelles
Golgi vesicles
Which organelle isolates hydrolytic enzymes?
(Hydrolytic referred to as hydrolase’s,split different groups of biomolecules)
Lysosomes
What 2 organelles are separate from the cytoplasm so metabolic reactions are contained?
Mito and chloroplasts
Which organelle provides an internal transport system?
Golgi vesicle
Describe phospholipids
2 fatty acid (lipid) tails at centre of cell membrane, hydrophobic, repelled by water so orientated themselves inwards
Phosphate group and glycerol (phospho) head face the outside of cell membrane. Hydrophilic, attracted to water.
Bilayer.
(Answer on Samsung notes) What why is it called the fluid mosaic model and why was it suggested?
Suggested as a means of explaining the cell surface membrane…
Why does the phospholipid not have a 3rd fatty acid/ hydrocarbon tail
Not a triglyceride as it has that phosphate group
Importance of the phospholipid bilayer?
Faster diffusion rate (simple diffusion if molecules are non-polar and small enough to move through membrane)
Controls entry and exit of some molecules (can act as a barrier to dissolved substances as hydrophobic tail prevents polar/water-soluble/ large substances that move by carrier or channel protein)
Flexibility (they move constantly so allow membrane flexibility)
What are the functions of intrinsic and extrinsic proteins
Extrinsic glycoproteins act as receptors such as hormones (target cells) and cell recognition. They also help cells adhere together and provide structural support.
Intrinsic proteins include carrier and channel proteins. These individually have different functions, see other flashcards.
Why are cholesterol (lipid) molecules important?
Binds to fatty acid tails of phospholipids and regulate the fluidity of the membrane. Makes cell membranes less fluid by restricting movement of phospholipids and proteins is there forced to be packed more closely together;
which prevents water and dissolved ions from leaking out of the cell.
Also help to maintain shape of animal cells such as red blood cells that arent by other cells.
- increases fluidity at low temps so that’s it isn’t too rigid. Stabilising cell membrane at high temps by stopping it from becoming too fluid.
what is the RER?
Function?
A system of membranes enclosing a fluid filled space, surface covered with ribosomes.
- folds and processes PROTEINS (hence that have been made by ribosomes)
what’s the SER (smooth endoplasmic reticulum)?
- function?
similar to RER, no ribosomes.
- synthesis and processes LIPIDS.
which organelles have a double membrane?
nucleus (the envelope is a double I assume), mitochondria and chloroplasts.
- just think every organelles that contains some form of genetic material of their own will have a double organelle membrane (which is different to a cell-surface membrane).
what are photos take down a microscope called?
electron micrographs
read.
watch a video (one on ppt) on how to recognise organelles and orientations of them in relation to other organelles.
- also mitochondria being a case where it may look different depending on the way a cell is squashed (may be sausage or circular shape)
Organelles in specialised cells, example of epithelial cells in small intestine (3)
- the walls of small intestine have many finger like protections called villi; ^SA for absorption.
- epithelial cells have folds on cell-surface membrane called microvilli, further ^ SA.
IMPORTANT TO MENTION MEMBRANE. - many mitochondria, providing energy for transport of digested food molecules across the cell into the blood via active transport (e.g. of glucose), against conc. gradient, which requires energy.
- another example: ribosomes may be in high numbers for protein production (such as glandular muscles that secret enzymes, which are proteins).
3 roles of golgi apparatus
- processes and packages new lipids
- processes and packages new proteins made
- makes lysosomes
- so endoplasmic reticulums further fold and process these molecules (SER on top of this synthesis LIPIDS)
Explain the process of exocytosis
- vesicles rise to cell-surface membrane through cytoplasm
- vesicles disintegrates or fuses/modifies the membrane
- proteins (or waste products such as used lysosomes?) released to extracellular environment that they diffuse into
What 5 organelles, in order, are responsible for synthesising proteins?
- nucleolus
- ribosomes (manufacture of unique sequence)
- RER (folding and processing)
- golgi body (packages and modifies final protein)
- golgi vesicles (responsible for exocytosis)
Adaptations of chloroplasts
- chlorophyll substance absorbs light: contained in MANY thylakoids - units of these are arranged in structures called grana, increasing SA (to allow to capture maximum light for photosynthesis).
- surrounded by watery solution of stroma (not sure how this is helpful).
Examples of where some organelles may be high in frequency within a cell (acknowledge vaguely)
- WBCs have many lysosomes yo hydrolyse the engulfed pathogens using their enzymes within.
- many sperm in mitochondria to swim and mice flagellum. This organelle is the site or respiration that produces ATP for the cell movement.
- RBCs dont have many organelles to increase SA for more oxygen to bind to the haemoglobin; maximise its transportation.
3 carbohydrates that are absorbed by the epithelial cell in the small intestine
glucose, fructose, galactose
which organelle synthesised glycoproteins
golgi body
organs are…
a combo of different tissues working together to carry out a specific function
why is artery an organ, whereas blood capillary is not?
artery: many tissues working together in its wall for example.
Capillary is just one tissues type.
5 comparisons between prokaryotic and eukaryotic cells
- eukaryotic has membrane bound organelles, other doesn’t
- nucleus and DNA attached to histones vs free singular circular DNA in cytoplasm
- binary fission vs mitosis / meiosis
- larger ribosomes in eukaryotes
- cell walls with either chitin or cellulose vs MUREIN cell wall
- prokaryotic DNA not associated w/ histones or proteing
Describe binary fission
(a sexual reproduction)
-this division also, as a side note, occurs rapidly in the right conditions.
- genetic info replicates (so circular DNA mostly but if a species has plasmids then that too: plasmids may also replicate many times)
- organelles move to opposite poles of the cells and so separating (the plasmids) randomly & 2 circular DNA separating: cell increases in size because of this
- Cells cytoplasm begins to split, cell-surface membrane divides the organelles … CYTOKINESIS
- 2 new separate bacterial cells have been split from the original one (aka 2 daughter cells, each with one copy of the circular DNA)
what is the purpose of a bacteria capsule?
allows to stick to other bacteria or gut walls for example.
also it is protective
purpose of flagellum
propels the cell, for movement (locomotion)
why are viruses classed as a cellular?
they have no cell membrane and aren’t alive (they don’t respire and need a host cell to replicate, as cant carry out reproduction, also rely on hist cells to carry out metabolic reactions).
- no nutrition, no energy, cant survive
What are the following functions of the viral structures?
1. Genetic material
2. Capsid
3. Attachment protein
- codes for viral proteins !
- protects the genetic material DNA/RNA
- binds to receptors on cells
tip for remembering difference between capsule and capsid.
capsule that surrounds bacteria, think you have to take antibiotics usually in capsule form to target bacterial infections.
Explain viral replication [5 points]
- Attachment proteins attach to * complementary receptors on (host) cell
- Genetic material / RNA enters cell
- Reverse transcriptase enzyme from the cell converts RNA to DNA, and the viral DNA inserts itself into the host cell DNA
- Viral proteins / capsid produced in ribosomes (and other organelles from cell are used)
- Virus particles then assembled and released, killing the cell as many burst out.
Which part of a virus decides the shape and number of attachment proteins on its surface?
Its genetic material / DNA or RNA
Pathogens
Viruses, protists, some fungi, parasites, bacteria
Viral replication
the creation of new viruses within host cells during infection
Describe the plasma membrane and cell wall of a prokarydre such as bacteria
Like eukaryotes: the plasma membrane is mainly made of lipids and proteins, controls movement of substances.
Cell wall supports & prevents cell lysis or changing shape. Made of polymer murien (that is made from glycoproteins)
Read (virus facts)
Viruses are just nucleic acids surrounded by protein : unlike bacteria, they have no cytoplasm, no plasma (cell-surface) membrane, no ribosomes.
resolution
detail and ability to distinguish between 2 points: if microscope can’t separate 2 objects, ^ magnification won’t help
the highest resolving power of TEM cannot always be achieved in practice because:
- difficulties preparing specimen (staining is hard and appearance of artefacts) limit the ultimate resolution achieved
- higher energy electron beam required, this may destroy the specimen
describe how TEMs work
They use electromagnets to focus a (singular) beam of electrons to be transmitted THROUGH the thin, dead specimen. Denser parts absorb more electrons, so appearing darker (bright areas allow more electrons to pass through).
Can see organelles in the cell due to HIGHEST resolution, and it’s a 2D image.
TEM limitations
- whole system must be in a vacuum, living specimens cannot be observed
- complex staining process, yet also no colours (interesting)
- specimen must be extremely thin
- image may contain artefacts (these appear on photomicrograph, but aren’t on actual specimen, can’t be sure of what exists)
what are artefacts? How do they come about?
Things that appear on photomicrographs but aren’t actually part of the specimen, such as dust or air bubbles.
They come from errors preparing the specimen or slide (or during staining)
describe how SEMs work
- all about scattering and lower resolving power than TEM.
it directs a beam of electrons across the surface of specimen. The beam is passed back & forth across the specimen in a regular pattern : electrons bounce and scatter, and the pattern of scattering detected depends on the contours of specimen, which can produce a 3D image.
These are used on thick specimens.
limitations of SEMs
- can’t view organelles
- complex slide preparation (may cause artefacts)
- lower resolution
- (may be more of a point for TEM) must be in an area free of electric / magnetic interference
Why electron microscopes can resolve better than light?
Electrons use a beam of electrons accompanied with a smaller wavelength, whilst light microscopes have a longer wavelength.
Explain why specimens must be kept in a vacuum to be viewed effectively using an electron (TEM) microscope
The beam of electrons can be absorbed by air molecules, preventing these electrons from properly reaching the specimen. May then be unclear which parts are denser, for example.
magnification calculation
I / (MxO)
may require conversion, mm and um (micro), then even nm.
for magnification, may have to use a scale bar.
watch a video on stage micrometers and eyepiece graticules.
scale bars
The scale bar shows the actual length of the image in real life, so in the calculation, scale bar is classed as the real object (look on topic 2 notes)
1. measure scale bar with ruler, then get “image” size by scale bar value.
2. perform conversions
3. calculate for magnification.
3 processes to eventually look at the structure of a particular organelle in a cell.
- homogenisation
- filtration
- ultracentrifugation
Describe the process of homogenisation, and explain the reasoning for the conditions
Used to breakup plasma membrane to RELEASE the organelles, done by vibrating the cells / tissue (eg. sound waves), or grinding in a blender.
Resulting fluid (of tissue and specific solution) = homogenate.
Must occur in: ice cold, isotonic, buffered solution.
Ice cold: reduce enzyme activity (avoids breaking down organelles)
isotonic: the solution has the same water potential (prevents osmosis, to avoid bursting or distorting the organelle’s shape)
buffered: maintains pH of organelles (proteins aren’t denatured)
Describe the filtration process
Why is it used?
Original mixture goes through filter paper in a funnel that passes into a separate test tube.
This is to remove unbroken cells or tissues or large pieces of debris.
Ultra centrifugation: (process on topic 2 notes)
- What is the initial liquid that is centrifuged?
1. Name given to contents forced to bottom of test tube?
2. Why largest & densest contents are spun at a lower speed.
3. Name given to liquid contents after a round of centrifugation?
4. How is ^ liquid separated from the bottom contents?
5. How are the next largest contents then separated?
6. 2 parameters used when separating organelles during ultracentrifugation?
- The filtered solution from previous processes
1. Pellet (unbroken, insoluble cells)
2. Densest organelles need the least amount of force to go to bottom
3. Supernatant
4. Liquid supernatant poured into new test tube
5. Spun at higher speeds, greater pressure required
6. mass & density - note that you keep repeating at higher speeds until all lighter organelles, or desired organelle, has separated out where they will be found in the pellet
Order of organelle density and mass :
Naughty Clever Monkeys Like Eating Raspberries
NCMLER
Nuclei
Chloroplasts
Mitochondria
LYSOSOMES
E. Reticulum
Ribosomes
How did scientist previously distinguish between artefacts and cell organelles?
Scientists distinguished between artefacts and organelles using electron microscopes by analyzing the images for known structures, comparing with light microscope images, and using staining techniques
lysis
Disruption of cells / organelles by rupture of their outer membrane
Advantages of light microscopes
Sample can be alive, colour, and easy setting up samples
What are glycoproteins and glycoplipids?
3 main uses.
Glycoprotein are chains of carbohydrates attached to a protein.
Glycolipids are chains of carbohydrates attached to phospholipids on the cell surface membrane.
- They’re signal receptors for hormones and neurotransmitters
- Receptors involved in endocytosis
- Receptors involved in cell adhesion and stabilising (the carbohydrate chain can form hydrogen bonds with water molecules surrounding cells, fun fact)
Give 2 things that should be done with the colorimeter before it is used to measure the absorbance of the liquid samples.
- Change the colour being detected on the settings (e.g. a blue filter)
- change the settings to absorbance and calibrate the colorimeter using water.
Briefly describe why cell membranes are affected by temperature
Temperature affects the phospholipid movement which can then affect the structure and permeability of the membrane as a whole.
What effect does below 0°C have in membrane permeability, and why?
MORE permeable:
ice crystals can form and pierce the membrane, holes are then made when the ice thaws
- damaged is caused, only reason it becomes more permeable
What effect does 0-20°C have in membrane permeability, and why?
LESS permeable:
the membrane molecules have less kinetic energy and aren’t moving as freely, which in turn makes the structure more closely packed together, and so may be harder for substances to enter (reducing membrane fluidity)
What effect does below 20-45°C have in membrane permeability, and why?
MORE permeable:
molecules have an increase in kinetic energy, they can move more freely (substances may enter more easily therefore), and membrane fluidity increases.
What effect does above 45°C have in membrane permeability, and why?
MORE permeable:
phospholipid bilayer may melt!
both channel and carrier proteins can denature, so cannot control the exchange of substances .
From your knowledge of cell membranes, what 2 properties should a drug possess if it is to enter a cell rapidly?
- non polar and lipid soluble
- small
suggest a function of the membrane surrounding the chloroplast (as there’s 2)
enzymes can’t leave the organelle, making photosynthesis more efficient
CI- ions need to get inside the cell. Suggest how they might move across the membrane
Carrier proteins (As carrier proteins change shape when they bind to ions/ molecules like glucose or amino acids)
Suggest the function of the membrane surrounding the bacterial cell
Allow substances in and out the cell & for cell signalling
The protein content on a typical cell membrane is around 50%. In energy releasing organelles, such as mitochondria, the amount is around 75%. Suggest why
Energy-releasing organelles require lots of substances (e.g. nutrients, enzymes, ATP) to travel across their membranes. Some of these substances will need to use proteins to get across the membrane, so these membranes will have a higher protein content.
Describe the movement of proteins within the bilayer
The molecules move relative to one another, and some move sideways (1) (flexibly - allowing substances in / out) and it’s always moving (1).
Describe the movement of proteins within the bilayer
The molecules move relative to one another, and some move sideways (1) (flexibly - allowing substances in / out) and it’s always moving (1).
hydrophilic
attracts water
role of cholesterol (2)
Helps membrane be less fluid and so more stable. Creates a barrier to polar substances.
fluid
phospholipids in bilayer always moving
How does the cell - surface membrane control what enters/leaves the cell?
Some proteins in it allow large or charged particles that would otherwise find it difficult to cross the membrane
Why facilitated diffusion is described as passive?
No ATP from respiration used, only energy used is the normal kinetic energy of the molecules themselves.
selectively permeable membrane
permeable to water molecules & small ones BUT not larger molecules
Why term co-transport is used to describe transport of glucose into cell
glucose and sodium ions more in coupled together
Explain why a cell membrane is an effective barrier against water-soluble substances
centre of phospholipid bilayer is hydrophobic, so membrane doesn’t allow water - soluble substances through
How may cells themselves be adapted for rapid transport across their internal and externor membranes?
by an increase in surface area or by an increase in the n° of channel / carrier proteins in their membrane
What is the concentration gradient?
The measure of the difference in concentration on either side of the exchange surface (particles diffuse quicker if steeper).
3 factors affecting diffusion
- Conc. gradient (^ rate: such as ventilation & blood circulation)
- Thickness of exchange surface (distance to travel, e.g. one cell
- Large surface of exchange surface (not necessarily SA : V that’s for whole organisms)
Apart from 3 factors for diffusion, what are some other factors that may affect diffusion across the phospholipid bilayer
- Optimum temperature (kinetic energy of diffusing particles, also intact protein structure and ideal fluidity of the phospholipids).
- Number of channel / carrier proteins, more increases the rate.
- Size and charge of particles - lipid soluble / non - polar diffuse quicker through phospholipid bilayer. water soluble and polar diffuse slower through proteins.
What is facilitated diffusion?
Net passive movement of molecules from Q region of high concentration to a region of low concentration across a carrier/ channel protein (depending on the type of molecule).
Describe the nature of carrier proteins, and what type of substances diffuse via it.
They only open when a complementary shaped molecule binds with it.
This causes a change in shape of the carrier protein, allowing it through.
- mainly large (and charged ions? and non lipid soluble, like Cl-) molecules
Describe the nature of channel proteins and what can diffuse via it
They’re pores in the membrane but only allow correct size molecules (small). These tend to polar molecules and water, down concentration gradient!
Side note that different channel proteins facilitate the movement of different charged particles.
What are some similarities and differences between the Z types of protein transporters?
similarities
1. Selective in the sense only some particles can pass through ( e.g. small or complementary ones)
2. Both sensitive to plH and temperature
3. Facilitated diffusion occurs across it: from high to low conc.
differences
1. No binding and changing shape occurs in channel proteins
Describe briefly how a carrier protein transports molecules across a cell membrane?
A large molecule with a complementary shape to fit the carrier protein, the protein then changes shape and opens on the other side, allowing for the substance to move into the cell by facilitated diffusion.
at a level you would describe osmosis in terms of…
water potential
define osmosis
The net, passive passage of H2O molecules from a region where there’s a higher water potential to a region of lower water potential through a selectively permeable membrane.
- or down water potential gradient
What’s water potential?
The pressure created by water molecules pushing against cell membranes (kPa), pure water = 0
More solute lowers the potential (for water to move, as l describe it), a more negative value indicates more pressure).
BY osmosis, which is a passive process
isotonic solution
same water potential: equilibrium
formula for making a dilution series of different concentrations using a stock solution
- this can be used in the osmosis practical
C1 × V1 = C2 × V2
V1= (0.4 × 15) / 1
so you now know you need 6 cm³ of stock solution, for example
15-6 = 9 cm³ of water needed
% change in mass
change in mass/ initial mass × 100
- ignoring anomalies and ensuring table has the same value, e.g. to 1 decimal place
define active transport
An active process whereby molecules/ ions move in and out of a cell from a region of lower concentration to a region of higher concentration using carrier proteins! and energy in the form of ATP (the energy released from its hydrolysis) through a partially permeable membrane
- against conc. gradient
Why is mitochondria and its structure relevant to ATP (adaptations)
The site of aerobic respiration, producing ATP, as its hydrolysis releases energy needed for active transport to move molecules against the concentration gradient.
The cristae (folded inner membrane) creates a larger SA to hold more enzymes on its surface associated with aerobic resp.
note
reminder hydrolysis of ATP is reversible reaction
What other factors may affect the rate of active transport
some examples include:
rate of ATP/glucose production
the number of (e.g. sodium…) carrier proteins
number of mitochondria (aerobic resp site, energy in the form of ATP)
- presence of inhibitory chemicals: stop/ slow active transport
In the production of urine, glucose is initially lost from the blood but then reabsorbed by kidney cells. Explain why it is important that this occurs via active transport rather than by diffusion
Diffusion - would eventually reach equilibrium of conc. so wouldn’t allow total reabsorption
Active t - allows moles to pass against conc. gradient, actively.
This way ( all ) glucose molecules can re - enter ; crucial to have many of these moles as they’re useful in many ways - aerobic respiration.
How does active transport work?
2 molecules BIND at the complementary BINDING site of the carrier protein.
Molecules are then able to be transported against the conc. gradient aided by the hydrolysis of ATP, which releases (chemical) energy. This allows the carrier protein to transport the molecules across the cell membrane
In the ileum, how is glucose and amino acids absorbed?
Glucose & amino acids continuously move by facilitated diffusion (from the small intestine lumen to the bloodstream) down a conc. gradient.
HOWEVER, only about 50% of absorption can happen this way due to equilibrium.
So, the rest of these substances must be absorbed by co-transport (it’s important all glucose molecules are absorbed for aerobic resp, releasing energy for other processes such as cell division or protein synthesis).
- neither of these processes are active at any point for these substances
define co-transport
The transport of 2 different molecules across the membrane through a (specific, complementary) carrier protein.
One molecule is transported against their concentration gradient (without requiring energy), along with a second molecule that is transported down its concentration gradient.
No energy is directly involved.
Ileum
section of small intestine where small, soluble food molecules are absorbed across the epithelium into the blood.
- Duodenum of the small intestine (unsure if need to know): large food molecules digested by enzymes from pancreas
3 adaptations of the villi for rapid diffusion
Large SA (microvilli)
Maintain conc. gradient (blood flow through many capillaries)
Short diffusion pathway (one cell thick)
products of digestion: the 3monosaccharides, from lipids, and from proteins
- glucose, fructose, galactose
- glycerol & 3 fatty acids
- amino acids
Info on micelles on topic 2 notes
…
How do lipid droplets turn into micelles?
Large droplet emulsified by bile.
These now smaller droplets (that have a larger SA for enzyme action) are hydrolysed by lipase into micelles
How are chylomicrons formed?
Triglycerides (from previous micelles) combine w/ modified proteins in the golgi body. This forms chylomicrons.
Bile: produced, stored, and roles?
Made in liver, stored in gall bladder: neutralises pH in stomach (for enzyme action), emulsifiers fats (large to small)
How the products of lipid digestion are absorbed?
- monoglycerides and fatty acids are emulsified by bile salts to form micelles (they stick these 2 molecules together)
- fatty acids and enter the epithelial cell (by diffusion) as micelles disintegrate upon contact of ileum lining, and link to form triglycerides
- Triglycerides combine with modified proteins in the golgi body = chylomicrons (vesicles?)
- Chlyomicrons diffuse out the epithelial cell, exocytosis occurs, and they enter the lacteal to be transported away from the small intenstine
which 3 organelles would be high in frequency in epithelial cells lining the ileum?
mitochondria, golgi body and smooth endoplasmic reticulum (lipids)
describe the role of exopeptidases
hydrolyses the peptide bond in the polypeptide chain, removing singular amino acids off the ends of the chain
do all cell in multicellular organisms retain the ability to replicate?
Not all, some include epithelial cells and hair follicle cells. So the ones that do follow a cell cycle >
What does the cell cycle consist of?
Mitosis is where the cell cycle starts and /or ends.
Interphase:
Then, gap phase 1 (G1): cell grows and new organelles / proteins made.
Synthesis stage (big one): cell replicates its DNA and it’s ready to begin dividing.
And, gap phase 2: the cell continues growing and proteins for cell division are made (spindle fibres)
What occurs generally in interphase?
Cell Carrie’s out normal functions, whilst also preparing to divide.
The cell’s DNA is unravelled and replicated, DOUBLING its genetic content!
The organelles are also replicated, AND its ATP content is increased (hydrolysis of it provides energy needed for cell division).
how can you tell a cell is in interphase
no visible chromosomes
why do cells undergo mitosis (2)
- increase cell number during growth
- replace cells during TISSUE repair
what are the 5 stages of the cell cycle (mitosis in detail)
Interphase (DNA replication)
Prophase (pre/proteins)
Metaphase (middle)
Anaphase (away)
Telophase (2 / tear)
Describe mitosis (4 stages)
- also on topic 2 notes
- Prophase
Nuclear envelope breaks down as the now more condensed (fatter and shorter) chromosomes lie in the cytoplasm.
Centrioles (protein bundles) move to opposite ends of the cell AND form a network of protein spindle fibres. - Metaphase:
Centromeres (that came from replication) line up at the equator, the spindle fibres attach. - Anaphase:
Both the centromeres and sister chromatids separate dye ti spindle fibres contracting and pulling them apart to opposite poles - as the centromere is pulled first. - Telophase:
(Chromatids have reached opp. poles)
It’s like undoing step 1 > chromosomes uncoil and nuclear envelope reforms around each group of chromosomes creating 2 nuclei.
Cytokinesis, 2 genetically identical daughter cells.
What is the similarity shared between chloroplasts, mitochondria and prokaryotic cells?
What does this suggest
The DNA all exists as circular molecules with no associated proteins.
Can gather these organelles originated as prokaryotic cells, and they become part of larger cells through evolution (perhaps due to moralistic relationships)
Explanations for believing a diagram shows the anaphase stage?
- Centromeres divided
- Each pair of sister chromatids are in the opposite poles of the cell
- V shape; suggesting spindle fibres contracted
Explain why: a root tip and a stain is used in investigations, and why tip was firmly squashed.
where mitosis is occuring, to highlight chromosomes so that they’re visible
(3D-2D) One cell layer thick so light can pass through and chromosomes be observed
A different set of results were obtained when the count was repeated with different garlic root tips. Give reasons (3+) for the difference in results.
- different MI / rate of mitosis occuring; so a genetic difference
- cells may spend different amounts of time in each stage
- temp / water availability / nutrient (if these arent control etc)
- age of root tip
- time of day
Explain why, in root tip squash, you must: “push down hard on the cover slip but not sideways”
- push hard to spread the tissue (one cell layer)
- avoid rolling cells and damaging them and break chromosomes
Mitotic index equation (used to find the proportion of cells undergoing mitosis as percentage or decimal)
MI = n° of cells with condensed chromosomes ÷ total n° of cells (×100)
What causes cancer and tumours, any comments on the treatment for them?
Uncontrolled cell division (mitosis is usually a controlled process otherwise) - treatments are directed at controlling the rate of cell division.
What is mitosis and the cell cycle controlled by? What does this tell you about tumours and cancer?
Controlled by genes: mutation in these genes makes cells keep on dividing when not necessary, and uncontrollably.
This forms a tumour, and cancer is a (malignant) tumour that invades surrounding tissue.
Define benign and malignant tumours.
Benign: generally don’t spread, surrounded by a membrane.
Malignant (officially a cancer): spread through bloodstream and lymphatic system to form secondary tumours throughout body.
Chemotherapy: some cancer treatments target/disrupt parts of the cell cycle in tumour cells using chemical drugs.
What are the 2 stages they target?
What are any problems with these drugs?
- G1 phase (cell growth and enzyme protein production), some chemical drugs prevent synthesis of enzymes needed for DNA replication - so then unable to enter S phase and disrupting the cycle. Cell kills itself.
- S phase (DNA rep.), radiation and some drugs damage DNA. DNA in cell cycle is regularly checked for damages. If severe damage is detected, cell kills itself - preventing further tumour growth!
These treatments don’t distinguish between normal and tumour cells, so kill normal dividing body cells. YET tumour cells divide more frequently so they are more likely to be killed.
how much is each singular division on a stage micrometer? (between each line)
0.1 mm long
Why use the meristematic tissue from the root tip?
Higher chance of the cells undergoing mitosis.
What is the mitotic index? What’s it used for.
Ratio between numbers of cell undergoing mitosis and total cells.
To see if an abnormal amount of cells are in the miotic stage: diagnose abnormal growth, suggest treatments (and to tests efficacy of drugs and interventions).
How much of the root tip is usually removed during preparation? Which 2 stains are commonly used in experiment?
5mm.
Aceto-orcein and toluidine blue (unsure if required to know).
How is the cancer tissue different in terms of cell cycle?
the cell cycle is more rapid
2 factors to consider when deciding what stain to use in root tip experiment.
- potential risks
- effectiveness of each stain
A higher MI than normal in organisms shows….
more cells are dividing than normal, due to survival response: injury so cellular repair e.g. or shows cancer
Function of glycoprotein [2]
Contains protein that is used in cell communication / signalling and found on the surface of the cell membrane.
Function of glycoprotein [2]
Contains protein that is used in cell communication / signalling and found on the surface of the cell membrane.
Function of glycolipid
Act as recognition sites (and antigens) and connecting cells together.
Help maintain the stability of the cell membrane.
Also used in cell signalling.
What’s the appearance of chromosomes in anaphase?
V shape where chromosomes are pulled to opposite poles AND CENTROMERES SPLIT
What’s the appearance of chromosomes in prophase?
Chromosomes condense and coil AND they become visible
What are microvilli
Projections from the villi in the ileum: (key) that is a highly folded cell-surface membrane
