2.1 Cell Structure Flashcards
What are the distinguishing features of eukaryotic cells?
● Cytoplasm containing membrane-bound organelles
● So DNA enclosed in a nucleus
Describe the function of the cell-surface membrane
● Selectively permeable → enables control of passage of substances in / out of cell
● Molecules / receptors / antigens on surface → allow cell recognition / signalling
Describe the function of the nucleus
● Holds / stores genetic information which codes for polypeptides (proteins)
● Site of DNA replication
● Site of transcription (part of protein synthesis), producing mRNA
● Nucleolus makes ribosomes / rRNA
Describe the structure of a ribosome
● Made of ribosomal RNA and protein (two subunits)
● Not a membrane-bound organelle
Describe the function of a ribosome
Site of protein synthesis (translation
Describe the function of rER and sER
rER
● Ribosomes on surface synthesise proteins
● Proteins processed / folded / transported inside rER
● Proteins packaged into vesicles for transport eg. to Golgi apparatus
sER
● Synthesises and processes lipids
● Eg. cholesterol and steroid hormones
Describe the function of Golgi apparatus and Golgi vesicles
Golgi apparatus
● Modifies protein, eg. adds carbohydrates to produce glycoproteins ● Modifies lipids, eg. adds carbohydrates to make glycolipids ● Packages proteins / lipids into Golgi vesicles
● Produces lysosomes (a type of Golgi vesicle)
Golgi vesicles
● Transports proteins / lipids to their required destination ● Eg. moves to and fuses with cell-surface membrane
Describe the function of lysosomes
● Release hydrolytic enzymes (lysozymes)
● To break down / hydrolyse pathogens or worn-out cell components
Describe the function of mitochondria
● Site of aerobic respiration
● To produce ATP for energy release
● Eg. for protein synthesis / vesicle movement / active transport
Describe the function of chloroplasts in plants and algae
● Absorbs light energy for photosynthesis
● To produce organic substances eg. carbohydrates / lipids
Describe the structure of the cell wall in plants, algae and fungi
● Composed mainly of cellulose (a polysaccharide) in plants / algae
● Composed of chitin (a nitrogen-containing polysaccharide) in fungi
Describe the function of the cell wall in plants, algae and fungi
● Provides mechanical strength to cell
● So prevents cell changing shape or bursting under pressure due to osmosis
Describe the function of the cell vacuole in plants
● Maintains turgor pressure in cell (stopping plant wilting)
● Contains cell sap → stores sugars, amino acids, pigments and any waste chemicals
Describe how eukaryotic cells are organised in complex multicellular organisms
Tissue -Group of specialised cells with a similar structure working together to perform a specific function, often with the same origin
Organ -Aggregations of tissues performing specific functions
Organ system -Group of organs working together to perform specific functions
What are the distinguishing features of prokaryotic cells?
Cytoplasm lacking membrane-bound organelles
● So genetic material not enclosed in a nucleus
Compare and contrast the structure of eukaryotic and prokaryotic cells
Has membrane-bound organelles (eu)
eg. mitochondria, endoplasmic reticulum
No membrane-bound organelles (pro)
eg. no mitochondria, endoplasmic reticulum
Has a nucleus Containing DNA (eu)
No nucleus DNA is is free in cytoplasm (pro)
DNA is long & linear & associated with histone proteins (eu)
DNA is short & circular & not associated with proteins (pro)
Larger (80S) ribosomes (in cytoplasm) (eu)
Smaller (70S) ribosomes (pro)
Cell wall only in plants, algae and fungi Containing cellulose or chitin (eu)
Cell wall in all prokaryotic cells Containing murein, a glycoprotein (pro)
Plasmids, flagella and a capsule sometimes present (pro)
Plasmids / capsule never present (sometimes flagella) (eu)
Explain why viruses are described as acellular and non-living
● Acellular - not made of cells, no cell membrane / cytoplasm / organelles
● Non-living - have no metabolism, cannot independently move / respire / replicate / excrete
Describe the general structure of a virus particle
- Nucleic acids surrounded by a capsid (protein coat)
- Attachment proteins allow attachment to specific host cells
- No cytoplasm, ribosomes, cell wall, cell-surface membrane etc.
- Some also surrounded by a lipid
envelope eg. HIV
Describe the difference between magnification and resolution
● Magnification = number of times greater image is than size of the real (actual) object ○ Magnification = size of image / size of real object
● Resolution = minimum distance apart 2 objects can be to be distinguished as separate objects
Describe and explain the principles of cell fractionation and ultracentrifugation as used to separate cell components
- Homogenise tissue / use a blender
● Disrupts the cell membrane, breaking open cells to release contents / organelles - Place in a cold, isotonic, buffered solution
● Cold to reduce enzyme activity
○ So organelles not broken down / damaged
● Isotonic so water doesn’t move in or out of organelles by osmosis ○ So they don’t burst
● Buffered to keep pH constant
○ So enzymes don’t denature - Filter homogenate
● Remove large, unwanted debris eg. whole cells, connective tissue - Ultracentrifugation - separates organelles
in order of density /mass
● Centrifuge homogenate in a tube at a low speed
● Remove pellet of heaviest organelle and respin supernatant at a higher speed
● Repeat at increasing speeds until separated out, each time the pellet is made of lighter organelles (nuclei → chloroplasts / mitochondria → lysosomes → ER → ribosomes)
