CELLS Flashcards
What is the structure of eukaryotic cells?
- Cell-surface membrane
- Nucleus
- Mitochondria
- Chloroplasts (in plants & algae)
- Golgi apparatus and golgi vesicles
- Lysosomes
- Ribosomes
- Rough Endoplasmic Reticulum
- Cell wall (in plants, algae & fungi)
- Cell vacuole (in plants)
What is the structure of prokaryotic cells?
- Cytoplasm (lacks membrane-bound organelles)
- Smaller ribosomes
- No nucleus (DNA free in cytoplasm)
- Cell wall containing murein (glycoprotein)
- One or more plasmids
- Capsule
- One or more flagella
Structure and function of cell-surface membrane?
- Found on surface of animal cells & just inside cell wall of others, mainly made of lipids & proteins
- Regulates movement of substances in & out of cell, also has receptor molecules allowing it to respond to chemicals like hormones
Structure and function of the nucleus?
- Surrounded by nuclear envelope (double membrane, contains many nuclear pores)
- Contains chromosomes (made from protein-bound linear DNA and nucleolus- which makes ribosomes)
- Controls cells activities, contains instructions to make proteins
- Nuclear pores allows substances to move between nucleus and cytoplasm
Structure and function of mitochondria?
- Double membrane (inner one folded to form structures called cristae. Inside is matrix, containing enzymes involved in respiration)
- Site or aerobic respiration, where ATP is produced
Structure and function of chloroplast?
- Small, flattened structure found in plant & algal cells
- Surrounded by double membrane, also has membrane inside thylakoid membrane (these membranes are stacked up in some parts of the chloroplast to form grana- linked together by lamellae which are thin, flat pieces of thylakoid membrane)
- Site of photosynthesis, some parts of photosynthesis occur in grana & other parts happen in stroma (thick fluid in chloroplasts)
Structure and function of golgi apparatus?
- Group of fluid-filled, membrane-bound flattened sacs, vesicles often seen at edges of sacs
- Processes/modifies and packages new lipids & proteins, also makes lysosomes
Structure and function of golgi vesicles?
- Small fluid-filled sac in cytoplasm, surrounded by a membrane & produced by golgi apparatus
- Stores lipids & proteins made by golgi apparatus & transports them out of cell (via cell-surface membrane)
Structure and function of lysosome?
- Round organelle surrounded by membrane, type of golgi vesicle
- Contains digestive enzymes called lysozomes which are kept separate from cytoplasm by surrounding membrane, can be used to digest invading cells or to break down worn out components of cell
Structure and function of ribosome?
- Very small organelle, either floats free in cytoplasm or is attached to rough endoplasmic reticulum
- Made up of proteins & RNA, not surrounded by membrane
- Site of protein synthesis
Structure and function of rough endoplasmic reticulum?
- System of membranes enclosing a fluid-filled space, surface is covered with ribosomes
- Folds & processes proteins that have been made at the ribosomes
Structure and function of smooth endoplasmic reticulum?
- Similar to RER, but no ribosomes
- Synthesises and processes lipids
Structure and function of cell wall?
- Rigid structure, surrounds cells in plants, algae & fungi
- In plants & algae, made mainly of carbohydrate cellulose
- In fungi, made of chitin
- Supports cells and prevents them from changing shape
Structure and function of cell vacuole?
- Membrane-bound organelle found in cytoplasm of plant cells, contains cell sap - a weak solution of sugar and salts. The surrounding membrane = tonoplast
- Helps maintain pressure inside cell and keep cell rigid. Stops plant wilting
- Also involved in isolation of unwanted chemicals inside the cell
What are specialised cells?
Cells which have specific adaptations to help them carry out their specific functions
How does a cell become specialised?
Process called differentiation:
- Unspecialised cells (stem cells) produce cells with specialised structures
- Stem cells: divide to replace damaged or old tissue, or new cells for growth
What is the structure and function of red blood cells?
- Small & flexible so can fit through narrow blood vessels
- Biconcave shape to maximise surface area or oxygen absorption
- Carry oxygen from lungs/gills to all body tissue and carry carbon dioxide (waste product of metabolism) to lungs where it’s excreted
What is the structure and function of a macrophage (white blood cell)?
- Large white blood cell, important part of immune system
- Born from white blood cells called monocytes, which are produced by stem cells in bone marrow
- Uses the process of phagocytosis to engulf particles & then digest them
- Some roam the body & some stay in one area
What is the structure and function of a sperm cell?
- Gamete produced in testicular organ of males
- Their tail propels the cell, also small & thin which aids their movement
- The head of sperm contains enzymes to digest exterior of the egg, allowing it to enter the egg & fuse with it
What is the structure and function of a neuron?
- Specialised cells that function to transmit electrical impulses within the nervous system
- They allow for rapid changes in an organisms internal and external environment
- Generate electrical signals called action potentials, allowing them to quickly transmit information over long distances
- Responsible for detection of stimulus, relay of impulse and stimulation of response
What is the structure and function of the epithelial cell?
- Cells that come from surfaces of body such as skin, blood vessels, urinary tract or organs
- Serve as barrier between inside & outside of body, and protect it from viruses
What is the structure and function of the stoma?
- Tiny pore in the surface of a leaf that is used for gas exchange
- The opening & closing of stomata are to regulate transpiration & allow gas exchange
- Diffusion of oxygen, carbon dioxide & water occurs rapidly when stomata are open
What is the structure and function of a root hair cell?
- Found in roots of plants
- Have a large amount of mitochondria which provide more energy for active transport
Structure and function of capsule?
- Some prokaryotes have this, eg bacteria
- Made from secreted slime & helps protect bacteria from attack by cells of the immune system
Structure and function of plasmids?
- Small loops of DNA
- Contains genes for things like antibiotic resistance & can be passed between prokaryotes
- Not always present, but some prokaryotes have several
Structure and function of flagella?
- Long, hair-like structure that rotates to make prokaryotic cell move
- Not all prokaryotes have one, but some have many
What is the structure of a virus?
- Acelluar (doesn’t contain a cell), non-living particles
- Smaller than bacteria (20-300nm)
- Contain nucleic acids such as DNA or RNA which is enclosed within a protein coat called capsid
- Can only replicate inside a living host
- Some are surrounded by envelope (lipid bilayer) or have attachment proteins to help bind to host cells
What is the process of binary fission?
- Circular DNA and plasmids replicate
- Cell gets bigger and DNA loops move to opposite poles of cell
- Cytoplasm begins to divide
- Cytoplasm divides & 2 daughter cells are produced, each with 1 copy of circular DNA & many copies of plasmids
How do viruses replicate themselves?
- Use their attachment protein to bind to complementary receptor proteins on surface of host cells
- Inject DNA/RNA into host cell, this hijacked cell then used its own machinery (eg enzymes, ribosomes) to replicate the viral particles
What is magnification?
How much bigger the image is compared to the actual size of the specimen
What is resolution?
The ability to distinguish between two close points
What is the magnification formula?
Magnification = Image size / Actual size
What is an optical microscope and how does it work?
- Uses light to form an image
- Max resolution of 0.2 micrometers
- Max magnification of x1,500
What is a transmission electron microscope and how does it work?
- Uses elcetromagnets to focus a beam of electrons which is transmitted through specimen. Denser part of specimen absorb more electrons, so appear darker on image
- High resolution, can see internal structures, only used on thin specimen
- Max resolution of 0.0002 micrometers
- Max magnification of x50,000,000
What is a scanning electron microscope and how does it work?
- Scans a beam or electrons across specimen and scatter
- Images show surface of specimen & are 3D, can be used on thick specimen
- Max resolution of 0.0002 micrometers
- Max magnification of x1,000,000
What are the types of cell fractionation?
Homogenisation:
- Break up plasma membrane (eg by grinding cells in blender) & release organelles into solution
- Ice cold solution = reduce enzyme activity
- Isotonic solution = same concentration as cell to prevent damage to organelles by osmosis
- Buffer solution added to maintain pH
Filtration:
- Solution filtered through gauze to separate large/tissue debris from organelles (organelles are smaller so pass through gauze)
Ultracentrifugation:
- Cell fragments poured into tube & put in centrifuge, spun and low speed. Heaviest organelles stay at bottom of tube & form thick sediment (pellet), rest or organelles stay suspended in fluid above sediment (supernatant)
- Process repeats and increasing speeds until all organelles are separated
What are the stages of the cell cycle?
Mitosis - cycle starts and ends here
G1- cell growth & new organelles & proteins are made
Synthesis - cell replicates DNA, ready for division by mitosis
G2- cell keeps growing, proteins needed for cell division made
What is the process of mitosis?
Interphase:
- Preparation for division, DNA unravelled & replicated
- Organelles replicated for spares
- ATP content increased for energy
Prophase:
- Chromosomes condense, become shorter and fatter
- Tiny bundles of protein (centrioles) start moving to opposite poles, forming network of protein fibres (spindle)
- Nuclear envelop breaks down & chromosomes lie free in cytoplasm
Metaphase:
- Chromosomes (each with 2 chromatids) line up along equator of cell & become attached to single by their centromere
Anaphase:
- Centromeres divide, separating each pair of sister chromatids
- Spindles contract, pulling chromatids to opposite poles of spindle, centromere first
Telophase:
- Chromatids reach opposite poles on spindle & uncoil to become long & thin (chromosomes)
- Nuclear envelop forms around each group of chromosomes, two nuclei
Cytokinesis:
- Cytoplasm divides, producing 2 daughter cells
How do you calculate the time for each stage of mitosis?
Number of cells in stage / total number of cells x total number of minutes in cell cycle
How is cancer a result of uncontrolled cell division?
- If there’s a mutation in a gene that controls cell division, the cells can grow out of control
- The cells keep dividing making more and more cells, forming a tumour
- Cancer is a tumour that invades surrounding tissue
What are treatments for cancer and how are they used?
Some treatments control the rate of cell division in tumour cells by disrupting the cell cycle - killing the tumour cells, but also killing normal dividing body cells.
Cell targets of cancer treatment:
G1- some chemical drugs (eg chemo) prevent synthesis of enzymes needed for DNA replication, so the cell is unable to enter S phase, disrupting the cell cycle & forcing the cell to kill itself
S phase- radiation & some drugs damage DNA. During cell cycle at many points DNA is checked for damage. If severe damage if detected, the cell will kill itself - preventing further tumour growth
Why is the cell membrane described as a fluid mosaic?
Fluid mosaic = arrangement of molecules in membrane
- Phospholipids form continuous bilayer which is fluid as they’re constantly moving
- Cholesterol molecules present in bilayer
- Proteins scattered through bilayer (including channel & carrier) which allow large molecules/ions to pass through, receptor proteins on cell-surface membrane allows cell to detect chemicals released from other cells
- Some proteins able to move sideways through bilayer, others in fixed position
- Some proteins have polysaccharide chain attached (carbohydrate) called glycoprotein
- Some lipids have polysaccharide chain attached called glycolipid
What is cholesterol?
- Type of lipid, present in all cell membranes (except bacterial)
- Fit between phospholipids & bind to their hydrophobic tails, causing them to pack closely together which restricts movement of phospholipids - making membrane less fluid & more rigid
- Helps maintain shape of animal cells, particularly important for cells that aren’t supported by other cells (eg red blood cells)
What is diffusion?
Net movement of molecules/ions from an area of high concentration to lower concentration, down a concentration gradient
Passive process - requires no energy
What does simple diffusion depend on?
- Concentration gradient: higher it is, faster rate of diffusion
- Thickness of exchange surface: thinner the surface (shorter diffusion pathway), faster rate of diffusion
- Surface area: larger it is, faster rate of diffusion
What does faciliated diffusion depend on?
- Concentration gradient: higher it is, faster rate of diffusion. As equilibrium reached, rate of faciliated diffusion levels off
- Number of channel/carrier proteins: once all proteins in membrane are in use, faciliated diffusion cannot happen any faster, even if you increase concentration gradient. So greater number of channel/carrier proteins, faster rate of faciliated diffusion
What is simple diffusion?
Molecules diffuse directly through cell membrane, down concentration gradient
What is faciliated diffusion?
Large/charged molecules diffuse through channel/carrier protein in cell membrane, down concentration gradient
What are carrier proteins and what do they do?
Move large molecules across membranes, down concentration gradient
- Large molecule attaches to it in membrane
- Protein changes shape
- Releases molecule on opposite side of membrane
What are channel protein and what do they do?
Form pores in membrane for charged particles to diffuse through, down concentration gradient
What is osmosis?
Diffusion of water molecules across a partially permeable membrane, from an area of high water potential to low water potential
What factors affect the rate of osmosis?
- Water potential gradient: higher the water potential gradient, faster the rate of osmosis
- Thickness of exchange surface: thinner the exchange surface, faster the rate of osmosis
- Surface area of exchange surface: larger the surface area, faster the rate of osmosis
What is active transport?
Uses energy (ATP) to move molecules/ions across membranes, against their concentration gradient
How are carrier proteins involved in active transport?
Molecule attaches to protein, changes proteins shape and this moves the molecule across the membrane, releasing it on the other side
What are the 2 main differences between active transport & faciliated diffusion?
- Active transport moves solutes from low to high concentration, faciliated diffusion is high to low
- Active transport requires energy (ATP), faciliated diffusion does not
What is a co-transporter?
A type of carrier protein
- Binds 2 molecules at a time
- Concentration gradient of 1 is used to move the other against its own concentration gradient
What factors affect the rate of active transport?
- Speed of individual carrier proteins: faster they work, faster the rate
- Number of carrier proteins present: more proteins, faster the rate
- Rate of respiration in cell and availability of ATP: if respiration is inhibited, active transport cannot take place
How is glucose/amino acids absorbed by co-transport?
- Sodium ions actively transported out of ileum epithelial cells into the blood via sodium-potassium pump. This lowers sodium ion concentration in epithelial cell, making sodium ion concentration in lumen higher (creates concentration gradient)
- Causes sodium ions to diffuse from lumen into epithelial cell, down their concentration gradient via the co-transporter proteins
- Co-transporter carries glucose/amino acid molecule into epithelial cell with sodium ion, concentration of glucose/amino acid inside epithelial cell increases
- Glucose/amino acid diffuses out of the epithelial cell into the blood, down its concentration gradient, through channel protein via faciliated diffusion
What are antigens and how are they used by the immune system?
Molecules that generate immune response when detected by body, usually proteins so have specific tertiary structure and found on surface of cells
Used by immune system to identify:
- Pathogens: diseases causing microorganisms
- Abnormal body cell: cancerous cells/tumours
- Toxins: released from bacteria
- Cells from other individuals of same species: organ transplant
What are pathogens?
Disease causing microorganisms that trigger an immune response eg bacteria, virus, fungi, protest
What are phagocytes?
Type of white blood cell that carries out phagocytosis
Found in blood and tissues
First cell to respond to an immune system trigger in the body
What are the 2 types of phagocytes?
Neutrophils
- Large, multi-lobed nucleus
- Produced in bone marrow, circulate blood in large numbers
- Highly mobile, squeeze through capillary walls into tissues, or onto epithelial cells surface eg the lungs
- Short-lived, but increase rapidly in numbers
Macrophages
- Larger than neutrophils, also made in bone marrow
- In blood, they circulate as monocytes, but then settle in body organs like lymph nodes & mature into macrophages
- Play a part in co-ordinating with specific immune response
What is the process of phagocytosis?
- Phagocyte recognises foreign antigens on pathogen & binds to antigens
- Cytoplasm of phagocyte moves around pathogen, engulfing it
- Phagosome is formed during this (endocytosis)
- Pathogen is now contained in phagocytic vacuole in cytoplasm of phagocyte
- Lysosome fuses with phagocytic vacuole, lysozymes break down pathogen
- Lysozymes digest pathogen - harmless products removed/used by phagocyte
- Phagocyte presents pathogens antigens - sticks antigens on its surface to activate other immune system cells
What are antibodies and where are they found?
Specialised protein made by plasma cells, which can bind to and help neutralise foreign antigens
Can be free in blood (or tear fluid), or used as receptors on the surface of white blood cells
What is the structure of antibodies and how does it relate to its function?
- 2 binding sites, so can bind 2 pathogens at same time
- Specificity depends on variable reigons, which form antigen binding sites
- Variable reigon with unique tertiary structure, complementary to specific antigen (all antibodies have same constant reigons)
- Hinge reigon in middle allows flexibility between branches of the Y shape
- Weakness of di-sulphide bridges allows them to move further apart to bind to more than 1 antigen at a time
- Quaternary structure (more than 1 polypeptide chain)
What are the functions of antibodies?
- Aggulutination: antibodies with more than 1 binding site can stick many pathogens together which can stop them spreading throughout body or make them too large to enter cells
- Neutralisation: by attaching to binding sites on pathogen, the antibody can prevent pathogen from binding to host cells, stopping them from entering. They may also neutralise toxins secreted by pathogen in same way
- Increase phagocytosis: by coating pathogens in antibodies, it makes it easier for phagocytes to bind to and engulf them
- Cell lysis: some antibodies work other molecules to ‘punch’ holes in pathogens’ cell walls, they’ll then burst when taking on water by osmosis (lysis)
- Reduce mobility: by attaching to flagella of bacteria, antibodies can make them less active so reduce ability of bacteria to move around
What is a lymphocyte?
Type of white blood cell, found in blood and lymph nodes
What is a T lymphocyte (T-cell)?
- White blood cells which contain receptors on their cell surface
- Made in bone marrow, mature in thymus gland
- Cannot recognise foreign antigens directly, but only respond when they are presented on surface of one of our own cells
What is a helper T cell?
- Receptor proteins bind to antigen on antigen presenting cells eg phagocytes
- This activates helper T-cell, which then stimulates B cell
- B cell clones & divides through mitosis before producing plasma cells which produce many antibodies
What is a cytotoxic T cell?
- Kill abnormal cells & body cells that are infected by pathogens
- Produce protein called perforin, that makes holes in cell-surface membrane
- Holes make cell membrane permeable to all substances & cell will then lyse (burst)
What is a B lymphocyte (B cell)?
- Produced in bone marrow, during embryo development
- Each B cell has one specific type of antigen receptor on its surface
- Antibodies bind to antigens on microbes cell surface and flag/label the microbe allowing phagocytes to recognise & destroy them easily
What is a cellular response?
T-cells and other immune system cells they react with
What is a humoral response?
B-cells, clonal selection & production of monoclonal antibodies
What is clonal selection?
Activating B-cells
- Complementary receptors on surface of B-cells bind to antigens and become antigen-presenting cells (APCs)
- APCs bind with active cloned helper T cell then are presenting the same complementary receptor
- One bound, helper T cell releases cytokines, which stimulate division and differentiation of the B cells
What do cytokines do?
Stimulate B-cells to divide and make two clones
What are the two types of B cells?
- B effector cells: these differentiate to produce plasma cells, which release antibodies into blood and lymph, only last few days
- B memory cells: remain for years and can respond with a higher concentration and more quickly to the same antigen in a future attack
What are the stages in immune response?
- Phagocytes engulf pathogens:
- Phagocyte recognises foreign antigens on pathogen
- Cytoplasm of phagocyte moves around pathogen & engulfs it
- Pathogen now in phagocytic vacuole in cytoplasm of phagocyte & lysosome fuses with it, breaking down pathogen
- Phagocyte presents pathogen’s antigens to activate other immune system cells - Phagocytes activate T-cells:
- T-cells receptor proteins bind to complementary antigen presented by phagocyte, activating the T-cell - T-cells activate B-cells
- Antibodies on B-cells bind to antigens & activates the B-cell (clonal selection)
- B-cell divides into plasma cells - Plasma cells make antibodies to specific antigen
- Plasma cells secrete monoclonal antibodies which bind to antigens on pathogen to form many antigen-antibody complexes
- Phagoctes bind to antibodies & phagocytose many pathogens at once
- Process leads to destruction of pathogens carrying the antigen in the body
What is a primary immune response?
When antigen enters body for first time & activates immune system
- Slow as aren’t many B-cells to make antibodies to bind
- Symptoms show
What is a secondary immune response?
If same pathogen enters body again, the immune system will produce a faster, stronger immune response
- Clonal selection happens faster & memory B-cells are activated to produce right antibody to antigen
- Memory T-cells activated & divide into correct type of T-cells to kill the cell carrying the antigen
- Often gets rid of pathogen before symptoms show
What are vaccines
Contain antigens that cause body to produce memory cells against a particular pathogen, without the pathogen causing disease
What is antigenic variation?
- Some pathogens change their antigens, so if you’re infected a second time, memory cells won’t recognise the different antigens, so a primary response is carried out
- Makes it more difficult to develop vaccines against some pathogens
- Example: influenza
What is active immunity and what types are there?
Where the immune system makes its own antibodies
- Natural: become immune after catching a disease
- Artificial: become immune after vaccination
What is passive immunity and what types are there?
When you’re given antibodies by a different organism
- Natural: baby becomes immune from antibodies it gets from its mother
- Artificial: become immune after injected with someone else’s antibodies
What are the differences between active and passive immunity?
Active immunity: - Requires exposure to antigen - Takes while for protection to develop - Memory cells are produced - Protection is long-term as antibody is produced in response to antigen being present in body Passive immunity: - Doesn't require exposure to antigen - Protection is immediate - Memory cells aren't produced - Protection is short-term as the antibodies given are broken down
What is HIV?
A virus which affects the immune system, leads to AIDS
What is AIDS?
Condition where immune system deteriorates & eventually fails
What is the structure of HIV?
- Core that contains genetic material (RNA) & some proteins
- Outer coating of protein = capsid
- Extra outer layer = envelope, made of membrane stolen from cell membrane of previous host cell
- Sticking out from envelope = copies of attachment protein to help HIV attach to host helper T-cell
What is the process of HIV replication?
- Attachment protein attaches to receptor molecule on cell membrane of host T-cell
- Capsid is released into cell, where it uncoats & releases RNA into cytoplasm
- Inside cell, reverse transcriptase is used to make complementary strand of DNA from viral RNA template
- From this, double-stranded DNA is made & inserted into human DNA
- Host cell enzymes used to make viral proteins from viral DNA within human DNA
- Viral proteins are assembled into new viruses, which bud from cell to infect other cells
What are symptoms/causes of AIDS?
- Initial symptoms include minor infections of mucous membranes & recurring respiratory infections
- As AIDS progresses, the number of immune system cells decrease so patients become more suspectable to infection
- During late stages of AIDS, patients have low number of immune system cells & can develop range of serious infections
How is HIV transmitted?
- Usually in blood or semen
- Via unprotected sex, through bodily fluids (eg sharing needles) and from HIV-positive mother to fetus across placenta or through breast milk
Why don’t antibiotics work against viruses?
- They kill bacteria by interfering with metabolic reactions, targeting bacterial enzymes & ribosomes
- Designed to only target bacterial enzymes & ribosomes, not human
- As human viruses use human enzymes & ribosomes to replicate, antibiotics cannot inhibit them as they don’t target human processes
- They also work by interfering with bacterial cell walls so water will enter, causing cell to burst & viruses dont have cell walls to they cannot interfere
Is there a cure for HIV?
No current cure
- Antiviral drugs can slow down progression of HIV & AIDS
- Best way to control HIV infection is to stop spread via unprotected sex
What are monoclonal antibodies?
- Antibodies produced by single group of genetically identical B-cells
- Produced outside of body
- Binding site has specific tertiary structure, so is specific to individual antigen
What is the ELISA test?
Uses antibodies to detect and quantify a protein
- Can be used to detect HIV & pathogens or diseases
- Useful where the quantity of an antigen needs to be measured
What is the process of the ELISA test?
- Apply sample to surface, which all antigens will attach
- Wash surface several times to remove any unattached antigens
- Add antibody to surface; which is specific to antigen
- Wash again
- Add another antibody, that will attach to first antibody (second antibody has enzyme attached to it)
- Add colourless substrate of the enzyme, enzyme acts on substrate to change it into a coloured product
- Amount of antigen present is relative to the intensity of the colour that develops
