2.1 Cell structure Flashcards
What is the structure and function of cell-surface membrane?
- Phospholipid bilayer with embdedded proteins
- Selectively permeable - enables control of passage of substances in and out of cell
- Barrier between internal and external environment of cell
What is the structure and function of the nucleus?
- Nuclear envelope, nuclear pores, nucleolus, DNA/chromatin
- Controls the cells activity through transcription on mRNA
- Nuclear pores allow substances eg/ mRNA to move between the nucleus and cytoplasm
- Nucleolus makes ribosomes which are made up of proteins and ribosomal RNA
- Where DNA replication takes place
What is the structure and function of the mitochondria?
- Double membrane - inner membrane folded to form cristae
- Matrix containing small 70s ribosomes, small circular DNA and enzymes involved in aerobic respiration (glycosis)
- Site of aerobic respiration producing ATP for energy release
What is the structure and function of the golgi apparatus?
- 3 or more fluid filled membrane bound sacs with vesicles at edge
- Recieves protein from rough endoplasmic reticulum
- Modifies/processes protein eg/carbs/sugars
- Packages into vesicle eg/ for transport to cell surface membrane for exocytosis
- Also makes lysosomes
What is the structure and function of lysosomes?
- Type of golgi vesicle containing lysozymes - hydrolytic enzymes
- Release of lysozymes to break down/hydrolyse pathogens or worn out cell components
What is the structure and function of the ribosomes?
- Float free in cytoplasm or bound to RER. Not membrane bound. 1 large and 1 small subunit
- Site of photosynthesis, specifically translation
What is the structure and function of the rough endoplasmic reticulum?
- Ribosomes bound by a system of membranes
- Folds polypeptides to secondary/tertiary structure
- Packages to vesicle, transport to the golgi apparatus
What is the structure and function of the smooth endoplasmic reticulum?
- Similar to RER but without ribosomes – system of membrane
- Synthesises and processes lipids
What is the structure and function of chloroplasts?
- Thylakoid membranes are stacked up in some parts to form grana, which are linked by lamellae. These sit in the stroma (fluid) and are surrounded by a double membrane. Also contains starch granules and circular DNA
- (Chlorophyll) absorbs light for photosynthesis to produce organic substances
What is the structure and function of the cell wall?
- Made mainly of cellulose in plants and algae, and of chitin in fungi
- Rigid structure surrounding cells in plants, algae and fungi. Prevents the cell changing
shape and bursting (lysis)
What is the structure and function of the cell vacuole?
- Contains cell sap – a weak solution of sugars and salts. Surrounding membrane is called the tonoplast
- Maintains pressure in the cell (stop wilting)
- Stores/isolates unwanted chemicals in the cell
How are specialised cells organised in multicellular organisms?
Specialised cell – the most basic structural/functional subunit in all living organisms; specialised for a particular function
Tissue – Group of organised specialised cells; joined and working together to perform a particular function; often with the same origin
Organ – Group of organised different tissues; joined and working together to perform a particular function
Organ system – Group of organised organs; working together to perform a particular function
How do prokaryotic cells differ from eukaryotics?
Prokaryotic cell cytoplasm contains no membrane bound organelles e.g. mitochondria WHEREAS eukaryotic cell contains membrane bound organelles
Prokaryotic cell has no nucleus / contains free floating DNA WHEREAS eukaryotic cell has a nucleus containing DNA
Prokaryotic DNA is circular and isn’t associated with proteins WHEREAS eukaryotic DNA is linear and is associated with proteins
Prokaryotic cell wall contains murein and peptidoglycan WHEREAS eukaryotic cell wall is made of cellulose
Prokaryotic cells have smaller 70s ribosomes WHEREAS eukaryotic cells have larger ribosomes
Prokaryotic cells may have…. one or more plasmid, a capsule, and/or one or more flagella
What are the different types of viruses?
- Acellular→not made of or able to be divided into cells
- Non-living → unable to exist/reproduce without a host cell
How do viruses replicate?
- Attachment proteins attach to receptors
- Viral nucleic acid enters cell
- Nucleic acid replicated in cell, reverse transcriptase makes DNA from RNA
- Cell produces viral protein
- Virus assembled and released from cell
How do optical microscopes work?
- Use light to form a 2D image
- Visible light longer
- Wavelength so lower
- Resolution 200nm
- Low magnification x1500
How do optical scanning electron microscope work (SEM)?
- Use electrons to form a 3D image
- Beams of electrons scan surface, knocking off electrons from the specimen, which are gathered in a cathode ray tube to form an image
- Electrons shorter wavelength (so higher resolution 0.2nm)
- High magnification x1500000
How do optical transmission electron microscope work?
- Use electrons to form a 3D image
- Electromagnets focus beam of electrons onto specimen, transmitted, more dense = more absorbed = darker appearance
- Electrons shorter wavelength (so higher resolution 0.2nm)
- High magnification x1500000
What are the advantages of the optical microscope?
☺Can see living organisms
What are the advantages of the scanning electron microscope?
☺3D image
☺High resolution; can see internal structures of organelles
☺High magnification
☺Used on thick specimens
What are the advantages of the transmission electron microscope?
☺High resolution; see internal structures of organelles
☺High magnification
What are the disadvantages of the optical microscope?
- 2D image
- Only used on thin specimens
- Low resolution; can’t see internal structures of organelles or organelles smaller than 200nm e.g. ribosomes
- Low magnification
What are the disadvantages of the scanning electron microscope?
- Vacuum; can’t see living organisms
- Lower resolution than TEM
What are the disadvantages of the transmission electron microscope?
- 2D image
- Only used on thin specimens
- Vacuum; can’t see living organisms
Definition of magnification
How much bigger an image of the sample is compared to the real size, measured by A = I/M
Definition of resolution
How well distinguished an image is between 2 points; shows amount of detail; limited by wavelength of radiation used
How do you measure the size of an object viewed with an optical microscope?
- Line up eyepiece graticule with stage micrometer
- Use stage micrometer to calculate the size of divisions on eyepiece graticule at a particular magnification
- Take the micrometer away and use the graticule to measure how many divisions make up the object
- Calculate the size of the object by multiplying the number of divisions by the size of division
- Recalibrate eyepiece graticule at different magnifications
How do you prepare a temporary mount of a specimen on a slide?
- Use tweezers to place a thin section of specimen e.g. tissue on a water drop on a microscope slide
- Add a drop of a stain e.g. iodine in potassium iodide solution used to stain starch grains in plant cells
- Add a cover slip by carefully tilting and lowering it, trying not to get any air bubbles
What are the conditions the sample of tissue must be placed in and why:
Cold - to reduce the activity of enzymes that break down organelles
Isotonic - to prevent water from moving into organelles via osmosis, which would cause them to expand
Buffered - to prevent organelle proteins from becoming denatured
Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells?
- Cell homogenisation breaks open the cells
- Filter to remove large debris
- Use isotonic solution to prevent damage to the mitochondria
- Keep cold to prevent damage to enzymes
- Centrifuge at a lower speed to separate nuclei
- Re-spin supernatant at a higher speed to get mitochondria out
