Cells ( Year 12 content ) Flashcards
What’s a eukaryotic cell?
A cell that has its DNA enclosed within a nucleas contains membrane-bound specialised organelles
What’s a prokaryotic cell?
A cell that has its DNA free floating in the cytoplasm and has extra rings of DNA called plasmids
Explain the role of cholesterol, glycoproteins and glycolipids in the cell-surface membrane
●Cholesterol:steroid molecule connects phospholipids and reduces fluidity.
●Glycoproteins:cell signalling, cell recognition(antigens), and binding cells together.
●Glycolipids:cell signalling and cell recognition.
Describe the structure of the nucleas
●surrounded by nuclear envelope, a semi-permeable double membrane
●nuclear Pores allow substances to enter/exit
●dense nucleolus made of RNA and proteins assembles ribosomes
Describe the function of the nucleas
●contains DNA coiled around chromatin into chromosomes
●controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis, and semi-conservative replication.
Describe the structure of a mitochondrion
●surrounded by a double membrane folded inner membrane forms cristae:site of electron transport chain
●Fluid matrix: contains mitochondrial DNA,respiratory enzymes,lipids,proteins
Describe the structure of a chloroplast
●vesicular plastic with double membrane
●Thylakoids:flattened discs stack to form grana;contains chlorophyll.
●stroma:fluid-filled matrix
State the function of mitochondria
Site of aerobic respiration to produce ATP
State the function of chloroplasts
Site of photosynthesis to convert light energy to chemical energy.
Describe the structure and function of the golgi apparatus
Planar stack of membrane-bound, flattened sacs cis face aligns with rER
●modifies and packages proteins for export
●synthesises Glycoproteins
Describe the structure and function of lysosome
Sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes Glycoprotein coats protect cell interior:
●digests contents of phagosome
Describe the structure and function of a ribosome
Formed protein and rRNA Free in cytoplasm or attached to rough ER.
●site of protein synthesis via translation
Describe the structure and function of the endoplasmic reticulum(ER)
Cisternae:network of tubules and flattened sacs extends from cell membrane through cytoplasm and connects to nuclear envelope:
●Rough ER:Many ribosomes are attached for protein synthesis and transport
●Smooth ER: lipid synthesis
Describe the structure of the cell wall
-Bacteria:
made of a polysaccharide called murein
-Plants:
made of cellulose
state the functions of the cell wall
-Mechanical strength and support.
-Physical barrier against pathogens
describe the structure and function of the vacuole in plants
surrounded by a single membrane, contains cell sap: mineral ions, water, enzymes
-controls turgor pressure
explain common cell adaptations
-Folded membrane or microvilli increase surface area
-many mitochondria= large amounts of ATP for active transport
-walls one cell thick to reduce distance of diffusion pathway
state the role of plasmids in prokaryotes
small ring of DNA that carries non-essential genes
state the role of capsule in prokaryotes
-provides mechanical protection against phagocytosis and external chemicals
-sticks cells together
what are the similarities between eukaryotic and prokaryotic cells?
both have:
-cell membrane
-cytoplasm
-Ribosomes
What are some of the differences between prokaryotic and eukaryotic cells?
●Prokaryotic cells contain circular DNA, whereas Eukaryotic cells contain linear chromosomes associated with histones
●prokaryotic cells contain 70S ribosomes, whereas eukaryotic cells contain 80S ribosomes
●Prokaryotic cells undergo binary fission, whereas eukaryotic cells undergo mitosis and meiosis
Why are viruses referred to as ‘particles’ instead of cells?
Acellular and non-living: no cytoplasm, can’t self-reproduce, no metabolism
Describe the structure of a viral particle
● contains RNA
● contains reverse transcriptase
● enclosed within a capsid
● contains attachemnet proteins
State the role of the capsid on viral particles.
● protects RNA from degradation by restricting endonucleases
State the role of attachment proteins on viral particles
Enables viral particles to bind to complementary sites on host cells
Describe how optical microscopes work
1) lenses focus rays of light and magnify the view of a thin slice of specimen
2) different structures absorb different amounts and wavelengths of light
3) reflected light is transmitted to the observer via the objective lens and eyepiece lens
Suggest the advantages and limitations of using ab optical microscope
Advantages
●produces a colour image
● can show living structures
● affordable
Limitations
● only produces 2D images
● lower resolution and magnification than electron microscopes= can not see ultrastructure
Describe how a transmission electron microscope (TEM) works
1) focus a high energy beam of electrons through thin slice of specimen
2) more dense structures appear darker since they absorb more electrons
3) Focus image onto fluorescent screen or photographic plate using magnetic lenses
Suggest the advantages and limitations of using a TEM
Advantages
● electrons have a shorter wavelength than light= high resolution, so ultrastructure visible
●High magnification( X500000)
Limitations
● 2D image
● requires a vacuum= a cannot show living specimen
● extensive preparation may introduce artefacts
● no colour images
Describe how a scanning electron microscope (SEM) works
1) Focus beam of electrons onto a specimens surface using electronmagnetic lenses
2) Reflected electrons hit a collecting devise and are applied to produce an image on a photographic plate
Suggest advantages and limitations of using an SEM
Advantages
● 3D image
● electrons have a shorter wavelength than light = high resolution
Limitations
● requires a vacuum=cannot show living structures
● no colour image
● only shows the outer surface
Define magnification
How much larger the image is compared to the actual size of the specimen
Define resolution
The minimum distance between 2 points in order for them to be distinguished 2 separate points
State an equation to calculate the magnification
Magnification= image size/ actual size
Outline what happens during cell fractionation and ultracentrifugation
1) Keep the tissue sample in a solution that’s cold,isotonic, and buffered
2) Break the tissue either mechanically(blender) or chemically( detergent) to break open cells and release organelles
3) filter the homogenate to remove debris
4) Put the filtrate in the test tube and put that test tube in a centrifuge and spin it
5) The most dense organelles in the mixture form pellets
6) filter off the supernatant and spin again at a higher speed
State the order of sedimentation of organelles during centrifugation
Most dense —> least dense
Nucleus —> mitochondria —> lysosomes —> RER —> plasma membrane —> SER —> ribosomes
Explain why fractionated cells are kept in a cold,buffeted,isotonic solution
Cold: slow action of hydrolase enzymes
Buffered: maintains constant pH
Isotonic: prevent osmotic cells/ shrinking of organelles
State what the cell cycle is and outline its stages
Cycles of division with intermediate growth peroids
1) interphase
2) mitosis or meiosis
3) cytokinesis
Explain why the cell cycle doesn’t occur in some cells
After differentiation, some types of cells in multicellular organisms( e.g. neurons) no longer have the ability to divide
What is the difference between the cell cycle and mitosis?
Cell cycle includes growth peroid between divisions; mitosis is only 10% of the cycle and referers to nuclear divisions
Outline what happens during interphase
G1: Cell synthesises proteins for replication and cell size doubles
S: DNA replicates= chromosomes consist of 2 chromatids joined at a contromere
G2: organelles divide
State the purpose of mitosis
Produces 2 genetically identical daughter cells for:
●growth
● cell replacement/ tissue repair
● asexual reproduction
Name the stages of mitosis
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
Outline what happens during prophase
1) chromosomes condense, becoming visible
2) centrioles form spindle fibres
3) Nuclear envelope breaks down= chromosome free in cytoplasm
Outline what happens during methaphase
Sister chromatids line up at the equator attached to the spindle fibres by their centromere
Outline what happens during anaphase
1) spindle fibres contract= centromere divides.
2) Sister chromatids separate into 2 distinct chromosomes and all pulled to the opposite poles of cell
Outline what happens during telophase
1) Chromosomes decondense, becoming invisible again
2) New nuclear envelope forms around each set of chromosomes
What are tumour suppressor genes
Genes that code for proteins to trigger apoptosis ( programmed death of damadged cells ) / slow down the cell cycle
What are oncogene
Genes that code proteins to stimulate cell cycle to progress from one stage to the next
How can mutations to tumour suppressor genes and oncogenes cause cancer?
●Tumour suppressor: no production of a protein needed to slow the cell cycle
●Oncogenes: form permanently- activated oncognes
● Dusrupution to the cell cycle—> uncontrolled cell division—> tumour
Suggest how cancer treatments control the rate of cell division
Disrupt the cell cycle:
● prevent DNA replication
● dusrupt spindle formation= inhibits metaphase/ anaphase
Outline how HIV replicates
1) Attachment proteins(GP120) attach to receptor(CD4) on host cell( T-Helper)
2)Reverse transciptase turns RNA into DNA, capsid opens up releasing the viral DNA into the T-Helper cells DNA
3) T-helper cells use viral DNA to make viral protein
4) viral proteins assemble to form the viral particle
How do new viral particles leave the host cell?
1) Bud off and use a cell membrane to form an envelope
2) cause lysis of host cell
Why is it so difficult to develop effective treatment against viruses?
Replicate inside living cells= difficult to kill them without killing host cells
What is an antigen?
●Cell-surface molecule stimulates immune response
● Usually glycoproteins, sometimes glycolipids
How does phagocytosis destroy pathogens?
1) phagocyte engulfs pathogen via endocytosis to form a phagosome
2) phagosme fuses with lysosomes(phagolysosome)
3) lysosomes secrete lysozymes that digest photogen
Explain the role of antigen-presenting cells(APCs)
Enhances recognition by T-Helper cells, which can not directly interface with pathogens/antigens in body fluid
Give 2 differences between specific and non-specific immune responses
●Nonspecific( inflammation, phagocytosis)= same for all pathogens
●Specific( B and T lymphocytes)= complementary pathogen
Nonspecific= immediate
Specific= time lag
Name the 2 types of specific immune response
●cell mediated
●humoral
Outline the process of cell mediated-response
1) pathogen engulfs by phagocyte
2) phagocyte becomes antigen presenting cell
3)T-helper cell binds to APC
4) T-helper cell divides to form more T-helper cells, T-memory cells and T-cytoxic cells
Outline the process of humoral response
1) B-cell engulfs the pathogen
2) B-cell becomes APC
3) T-Helper cells bind to antigens on B-cells
4) This initiates the cell division of B-cells into plasma cells and memory cells
5) Plasma cells secrete antibodies complementary to antigen
What is an antibody?
Proteins secreted by plasma cells
●Quaternary structure: 2 ‘light chains’ held together by disulfide bridges, 2 longer ‘heavy chains’
● Binding sites on variable regions of light chains have specific tertiary structures complementary to an antigen
● rest of the molecule is the constant region
How do antibodies lead to the destruction of a pathogen?
Formating of antigen-antibody complex results in agglutination, which enhances phagocytosis
What are monoclonal antibodies?
Antibodies that have the same tertiary structure
What are memory cells?
●specialised T-helper cells and B cells produced from primary immune response
●remain in low levels in the blood
● can divide rapidly by mitosis if organisms encounter the same pathogen again
Constrats the primary and secondary immune response
Secondary response:
● faster rate of antibody production
● shorter time lag between exposure and antibody production
● Antibody level remains higher after the secondary response
● pathogen usually destroyed before any symptoms
What causes antigen variability?
1) random genetic mutations change DNA base sequence
2) different sequences of codons on mRNA
3) different primary structures
4) different tertiary structures
5) different shapes of antigen
Explain how antigen variability affects the incidence of disease
●Memory cells no longer complematry antigen= individual not immune= can catch disease more than once
Compare passive and active immunity, and give examples of both types
1)Passive natural: antibodies in breats milk/ across the placenta
2)Passive artificial: injected with antibodies
3)Active natural: humoral response to infection
4)Active artificial: vaccination
Explain the principles of vaccination
1) The vaccine contains a dead/ weakened form of a pathogen
2) Triggers’ primary immune response
3) memory cells produced and remain in the bloodstream, so secondary reposnse is rapid and produces a higher concentration of antibodies
4) Pathogen is destroyed before it causes symptoms
What is herd immunity?
●Vaccinating large proportion of population reduces available carriers of the pathogen
●Protects individuals who have not been vaccinated
Suggest some ethical issues surrounding the use of vaccines
●production may involve use of animals
● potentially dangerous side-effects
● clinical tests may be fatal
Describe the structure of HIV
● Genetic material(RNA) and reverse transcriptase surrounded by capsid
●Surrounded by virla envelope
● GP120 attachment proteins on surface
How does HIV result in the symptoms of AIDS?
1) Attachment proteins(GP120) bind to complementary CD4 receptors on T-Helper cells
2) HIV particles replicate inside T-Helper cells, killing them
3) AIDS develops when there are too few T-Helper cells for the immune system to function
4) Individuals can not destroy other pathogens and suffer secondary diseases
Why are antibiotics ineffective against viruses
●Antibiotics often work by damaging murein cell walls to cause osmotic lysis. Viruses have no cell wall
●Viruses replicate inside host cells= difficult to destroy them without damaging normal body cells
Sugget the clinical applications of monoclonal antibodies
●pregnancy tests by detecting HCG hormones in urine
● ELISA test
● targeted treatment by attaching drugs to antibodies so that it only binds to cells with abnormal antigen
Explain the principles of the direct ELISA test
1) monoclonal antibodies bind to the bottom of the test plate
2) antigen molecules in sample bind to antibody. Rinse excess
3) Mobile antibodies with enzyme attached bind to antigens that are on the fixed monoclonal antibodies. Rinse excess
4) Add substrate for enzymes. Positive result: colour change
Suggest some ethical issues surrounding the use of monoclonal antibodies
●Production involves animals
Explain the functions of membranes within cells
●provide internal transport systems
● selectively permeable to regulate the passage of molecules into/ out of organelles
● provide reaction surface
● isolate organelles from cytoplasm for specific metabolic reactions
Define osmosis
The net movement of water from a high water potential to a low water potential across a partially permeable membrane
What is water potential?
●Pressure created by water molecules measured in kPa
● water potential of pure water at 25°C and 100kPa is 0
● more solute= more negative water potential
How does osmosis affect plant and animal cell?
● Osmosis into cell:
Plant: vacoule swells=cell turgid
Animals: lysis
● Osmosis out cell:
Plant: vacoule shrinks= cell flaccid
Animals= crenation
Define simple diffusion
The net movement of molecules from an area of high concentration to an area of low concentration
Define facilitated diffusion
The net movement of molecules from an area of high concentration to an area of low concentration requiring channel and carrier proteins
Explain how channel and carrier proteins work
Channel: hydrophilic channels bind to specific ions
Carrier proteins: a large molecule attaches to a carrier protein in the membrane, and the protein changes shape. This releases the molecule on the opposite side of the membrane
Name the 4 factors that affect the rate of diffusion
● Temperature
● Diffusion distance
● Surface area
● Difference in concentration gradient( how steep it is)
State Ficks law
Surface area x difference in concentration gradient/ diffusion distance
How are cells adapted to maximise the rate of transport across their membranes?
● many carrier/channel proteins
● folded membrane increases surface area
Define active transport
The movement of molecules from an area of low concentration to an area of high concentration requiring ATP and carrier proteins
Compare and contrast active transport and facilitated diffusion
●Both may involve carrier proteins
● active transport requires energy from ATP hydrolysis; facilaited diffusion is passive
● Faciliated diffusion may also involve channel proteins
Define co-transport
Movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration gradient
Explain how co-transport is involved in the absorption of glucose/ amino acids in the small intestine
1) Na+ ions actively transported out of epithelial cells and into bloodstream
2) Na+ concentration is lower in the epithelial cells than the lumen
3) When Na+ ion diffuses into the epithelial cell, it brings along glucose/amino acid with it
