Cells Flashcards
Structure of nucleus
- nuclear envelope
- nuclear pores
- nucleoplasm
- chromosomes
- nucleolus
What is the nucleolus
Site of rRNA production and makes ribosomes
Function of nucleus
- site of DNA replication and transcription
- contains the genetic code for each cell
Structure of eukaryotic cells
- cell-surface membrane
- nucleus
- mitochondria
- chloroplast
- golgi apparatus + vesicles
- lysosomes
- ribosomes
- RER + SER
- cell wall
- cell vacuole
RER + SER structure
- both have folded membranes called cisternae
- RER have ribosomes on the outer surface but SER don’t
RER + SER function
RER: provides large SA for protein synthesis + provides pathway for the transport of materials
SER: synthesise, store and transport carbohydrates and lipids
Golgi body functions
- add carbs to proteins to form glycoproteins
- produce secretory enzymes
- transport, modify and store lipids
- form lysosomes
Lysosomes structure
- Contain digestive enzymes like proteases and lipases
- they also contain lysozymes
What are lysozymes and what happened to them
- enzymes that hydrolyse the cell walls of certain bacteria
- lysosomes isolate these enzymes from the rest of the cell and then release them either to the outside or into a phagocytic vesicle within the cell
Functions of lysosomes
- break down material ingested by phagocytosis
- release enzymes outside the cell (exocytosis)
- digest worn out organelles
- completely break down cells after they’ve died (autolysis)
- hydrolyse phagocytic cells
Mitochondria structure
- double membrane -> outer one controls entry + exit of materials whilst inner is folded to form cristae
- matrix
What do mitochondria cristae do
Provide a large SA for the attachment of enzymes + are involved in respiration
What does the mitochondria matrix do
Contains proteins, lipids and traces of DNA and also its own ribosomes -> so mitochondria can control the production of their own proteins
Mitochondria function
- site of aerobic respiration
- site of ATP
- DNA to code for enzymes needed in respiration
Ribosomes structure
Made up of 2 sub-units containing protein and rRNA:
- 80S -> found in eukaryotic cells
- 70S -> found in prokaryotic cells, mitochondria and chloroplasts
Ribosomes function
The site of protein synthesis
Vacuole structure
Filled with fluid surrounded by a single membrane called tonoplast
Vacuole function
- make cells turgid and so provide support
- temporary store of amino acids and sugars
- the pigments may colour petals to attract pollinators
Chloroplasts structure
- double membrane
- contain thylakoids -> folded membranes with pigment
- fluid filled strings contains enzymes for photosynthesis
Chloroplasts function
Site of photosynthesis
Cell wall structure (plants and fungi)
Plants: made of micro fibrils of cellulose polymer
Fungi: made of chitin -> a nitrogen containing polysaccharide
Cell wall function
Provide structural strength to the cell
Cell membrane structure
- phospholipid bilayer -> molecules embedded within and attached on the outside
( proteins, carbohydrates, cholesterol)
Cell membrane function
Controls entry and exit of molecules
What things do cell membranes contain
- cholesterol
- glycoproteins
- glycolipids
- proteins
- phospholipids
Vacuole structure
- fluid filled sac, bound by a single membrane called a tonoplast
- a plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and pigments such as anthocyanins
Function of vacuole
- sugars and amino acids act as temporary food stores
- keeps the cells turgid
- pigments may colour petals to attract pollinating insects
Object
Material under microscope
Image
Appearance of material under a microscope
Resolution
The minimum distance apart that 2 objects can be in order for them to appear as separate items
Greater resolution = greater clarity
Light microscope
Uses light rays that pass through a specimen and are focused by the objective lens and eyepiece lens to produce an image
Light microscope resolution
Have a poor resolution due to the long wavelength of light
Electron microscope
Uses a beam of electrons -> an electromagnet is used to focus the beam of electrons on the specimen
Electron microscope resolution
Better resolution due to a shorter wavelength
What are the 2 types of electron microscope
Transmission and scanning
TEM Limitations
- whole system must be in a vacuum so living specimens can’t be observed
- a complex staining process
- image may contain artefacts
- only black and white
- specimen must be very thing, resulting in a flat 2D image
TEM Limitations
- whole system must be in a vacuum so living specimens can’t be observed
- a complex staining process
- image may contain artefacts
- only black and white
- specimen must be very thing, resulting in a flat 2D image
Scanning electron microscope
Directs a beam of electrons onto the surface, rather than penetrate it -> has a lower resolving power than the TEM
SEM limitations
- whole system must be in a vacuum so living specimens can’t be observed
- complex staining process
- image may contain artefacts
Why is cell fractionation possible
Due to the different densities or the organelles
What is cell fractionation
Process where cells are broken up and different organelles are separated out
What must you do before cell fractionation
Put the tissue in cold, buffered and isotonic solution
Why must the solution be cold, buffered and isotonic
Cold - to reduce enzyme activity that might break down the organelles
Buffered - to maintain constant pH as a change in pH could alter the structure of organelles or affect their functioning
Isotonic - to prevent any osmotic gain or loss of water so organelles don’t burst or shrink
What are the steps of cell fractionation
- Place in cold, buffered and isotonic solution
- Homogenisation
- Ultracentrifugation
What happens in homogenisation
- cells are broken up by a homogeniser -> this releases organelles
- the resultant fluid (homogenate) is filtered to remove any debris + complete cells
What happens in ultracentrifugation
- the fragments in the filtered homogenate are separated out in an ultracentrifuge
-> this spins tubes of homogenate quick to create a centrifugal force
What speed is the tube spin in ultracentrifugation
- slow at first -> the heaviest organelle (nucleus) is forced to the bottom where it forms a thin sediment or pellet
- the supernatant is removed and spun at a faster speed so the next heaviest organelle is forced to the bottom
How does a cell become specialised
Every cell contains genes needed for it to develop into a different cell BUT only some of these genes are switched on (expressed) and the rest of switched off
What is a tissue
A collection of similar cells that perform specific function
Examples of tissues
Epithelial and xylem
What is an organ
A combination of tissues coordinates to perform a variety of functions
What tissues does the stomach have
- muscle to churn and mix the contents
- epithelium to protect the stomach wall and produce secretions
- connective tissues to hold other tissues together
What tissues do leaves have
- palisade mesophyll made from palisade cells for photosynthesis
- spongy mesophyll for gaseous diffusion
- epidermis to protect the leaf and allow gaseous diffusion
What are the organ systems in animals
Digestive, respiratory and circulatory
Are eukaryotes or prokaryotes bigger
Eukaryotes are bigger
Structure of a bacterial cell
Cell wall - physical barrier that excludes certain substances and protects against mechanical damage and osmotic lungs
Capsule - protects bacterium from other cells and helps groups of bacteria stick together
Cell-surface membrane - controls entry + exit of chemicals
Circular DNA - holds the genetic info for the replication of bacterial cells
Plasmid - holds the genes that may aid the survival of bacteria in adverse conditions
Virus structure
(Acellular, nonliving)
- contain nucleic acids (like DNA or RNA) as genetic material -> enclosed within a protein coat called a capsid
- some viruses have a lipid envelope -> the lipid envelope (if present and capsid if not) have attachment proteins that allow a virus to identify and attach to a host cell
Prokaryotic and eukaryotic properties
Prokaryotic
- no nucleus
- DNA is not associated with proteins
- some DNA may be in the form of plasmids
- no membrane-bounded organelles
- no chloroplasts
- ribosomes are smaller (70S)
- cell wall are made of murein (peptidoglycan)
- may have a mucilaginous layer called a capsule
Eukaryotic
- have a nucleus with a nuclear envelope
- DNA is associated with proteins called histones
- no plasmids
- membrane - bounded organelles like mitochondria are present
- chloroplasts present in plants and algae
- ribosomes are larger (80S)
- where present cell wall is made out of cellulose (chitin in fungi)
- no capsule
What is the cell wall in fungi made out of
Chitin
Functions of membranes within cells
- control exit + entry of materials in organelles like mitochondria and cytoplasm
- separate organelles from cytoplasm so specific reactions can take place within them
- provide an internal transport system eg ER
- isolate enzymes that might damage the cell eg lysosomes
- provide surfaces on which reactions can occur eg protein synthesis on ribosomes on the ER
Structure of cell surface membrane
Phospholipid bilayer
What significant about phospholipids
They are polar as they have 2 ends that act differently
Function of the phospholipid bilayer in the cell membrane
- allow lipid soluble substances to enter and leave the cell
- prevent water soluble substances from entering and leaving the cell
- make the membrane flexible
What 2 ways are proteins embedded in the cell surface membrane bilayer
- Some are in the surface or partly embedded -> give mechanical support or act as cell receptors
- Others completely span the bilayer - some are protein channels to transport water soluble molecules across the membrane + others are carrier proteins that change shape and carry molecules across the membrane
Functions of proteins in the cell membrane
- structural support
- act as channels, transporting water soluble substances
- allow active transport across the membrane
- act as receptors
- help cells adhere to each other
How permeable is the cell surface membrane
Gene really most molecules don’t freely diffuse across it
Why don’t molecules generally freely diffuse across the cell membrane
- too large to pass through channels
- not soluble in lipids
- are the same charge as the charge on the protein channels > so are repelled
- are polar > so can’t pass through the non-polar hydrophobic tails
What does cholesterol do in the cell membrane
- add strength to the membranes
- very hydrophobic so help prevent loss of water and dissolved ion from the cell
- they also pull the fatty acid tails of the phospholipid molecules -> limiting their movement without making it too rigid
Function of cholesterol in the cell membrane
- reduces lateral movement of other molecules including phospholipids
- make the membrane less fluid at high temps -> prevents leakage of water + dissolved ions from the cell
What are glycolipids made from
A carbohydrate covalently bonded with a lipid
What other components does the cell membrane have
Cholesterol
Glycolipids
Glycoproteins
Function of glycolipids in the cell membrane
- act as recognition sites
- helps maintain the stability of the membranes
- helps cells to attach to one another and so form tissues
What are glycoproteins
Carbohydrate chains attached to extrinsic proteins on the outer surface
Function of glycoproteins in the cell membrane
- act as cell surface receptors
- act as recognition sites
- help cells to attach to one another and so form tissues
- allows cells to recognise one another
The fluid-mosaic model
- fluid -> the phospholipid molecules can move relative to one another
- mosaic -> proteins are embedded in the surface of the membrane like a mosaic
Types of movement across the cell membrane
- diffusion
- facilitated diffusion
- active transport
- osmosis
What is diffusion
Net movement of molecule or ions from an area of high concentration to an area of low concentration until evenly distributed
-> passive process (no energy needed)
What affects rate of diffusion
- conc gradient -> the greater the difference the faster
- area over which it takes place
- thickness of exchange material -> the thinner the faster
What is facilitated diffusion
Exactly like diffusion but protein and/or carrier proteins are involved
What proteins are involved in facilitated diffusion
Carrier proteins and protein channel
Structure of Protein channels
Water filled hydrophilic channels across the membrane
What do protein channels do
- allow specific water soluble ions to pass through
- the channels are selective -> only open in the presence of a specific ion which binds to them and causes them to change shape so it opens on 1 side and closes on the other
How do carrier proteins work
- when a specific molecule binds with the protein it causes it to change shape so that the molecule is released on the other side of the membrane
What is active transport
The movement of molecules of ions or out a cell from an area of lower concentration to an area of higher concentration using ATP and carrier proteins
How does active transport differ from passive forms of transport
- metabolic energy in form of ATP is needed
- substances are mixed against concentration gradient
- carrier proteins are used
- very selective process
Why does a graph of facilitated diffusion level off
Protein channels are saturated
What is osmosis
The movement of water from a region of high water potential to an area of lower water potential through a partially permeable membrane
What is water potential
The pressure created by water pressure
What is the water potential of pure water
Under standard conditions of temp and pressure it is 0
What does the addition of a solute to pure water cause
It will lower the water potential, so the water potential of a solution is always less than 0 (so a negative value)
What is hypotonic
The solution has a higher water potential than the inside of the cell so water moves in by osmosis
Hypotonic solution in animal cell
Animal cells swell up and will eventually burst as their cell membrane isn’t strong enough to withstand pressure (lysis)
Hypotonic solution in a plant cell
They swell up but don’t burst because their cell wall protects them -> their vacuoles expand and they become turgid as the cell membrane pushes on the cell wall
What is isotonic
No difference in water potential between the cell and surrounding solution so no net movement of water
What is hypertonic
When the solution has lower water potential than the inside of the cell so water will move out of the cell by osmosis
Hypertonic solution in animal cell
Animal cells will shrivel as they lose water from their cytoplasm
Hypertonic solution in plant cells
Plant cells are protected from shrinking but their vacuoles shrink and eventually their cell membranes pull away from the cell walls -> this is plasmolysis
Increasing the rate of movement across the ileum
The epithelial cells lining the ileum have microvilli which provide more SA for the insertion of carrier proteins
Why must active transport happen as well as diffusion in absorption
Because diffusion only works until the concentrations are equal meaning not all glucose and amino acids are being transported so active transport is used
What is the name for how amino acids and glucose are absorbed into the blood and why
Co-transport because the glucose or amino acids have been transported in along with sodium ions which have been actively transported out by the sodium-potassium pump
Where and how does the co-transport of glucose happen
In one type of protein-carrier molecule
- Na+ are actively transported out of the epithelial cells into blood
- This now leads to a lower concentration of Na+ in the cell
- This causes Na+ to move into the epithelial cells from the ileum by facilitated diffusion -> this also brings in a glucose molecule (co-transport)
- Glucose now moves down the concentration gradient from the epithelial cell to the blood by facilitated diffusion
What is it that powers the movement of glucose and amino acids into cells and why
Not ATP but the sodium ion concentration gradient as the glucose molecules are moving against the concentration gradient and the sodium ions are moving down it easily
Densities of organelles
Nucleus
Chloroplast
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes
What do the most dense organelles form at the bottom of the centrifuge
Pellets
What stage of the cell cycle requires ATP
Anaphase
Mitotic index
( Number of cells in mitosis/ number of cells in view ) x 100
What are peripheral proteins
Proteins on the cell surface membrane that don’t span the whole membrane
-> provide mechanical support and act as receptors for cell recognition
What are integral proteins
Proteins that span across the cell surface membrane
-> are protein carriers or channel proteins involved in the transport of molecules across the membrane
What are protein channels
Tubes that fill with water to enable to water soluble ions to diffuse
-> selective as channel only opens in the presence of certain ions
What do carrier proteins do
Bind with larger molecules like glucose and amino acids and change shape to transport them to the other side of the membrane
What kind of molecules require facilitated diffusion
Ions and polar substances
What is water potential
Pressure created by water molecules and is measured in kPa
Active transport process
- Transport is through carrier proteins spanning the cell membrane
- Molecule binds to a receptor complementary in shape on the protein
- ATP binds to the carrier protein from the inside of the cell and it is hydrolysed into
ADP +Pi - This causes the carrier protein to change shape and release the molecule to the other side
- The phosphate ion is then released and the protein returns to its original shape
Co-transport of glucose and sodium ions in the ileum
- Sodium ions are actively transported out of the epithelial cell into the blood
- This reduces the sodium ion concentration in the epithelial. cell.
- Sodium ions can then
diffuse from the lumen down their concentration gradient into the epithelial cell - The protein the sodium ions diffuse through is a co-transported protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient
- Glucose then moves by facilitated diffusion from the epithelial cell to the blood
