1.2 Cell Structure Flashcards
1mm to 1um to 1nm
x1000, x1000
1nm to 1um to 1mm
/1000, /1000
Define magnification
The number of times an image is compared with the real size of an object
Magnification equation
mag = size of image
———————
actual size
What is the Golgi body? What is its function?
- formed from vesicles from the RER fusing
- made of a stack of flattened membrane bound cavities
- package and modify proteins, package secretory enzymes, secrete carbs and glycoproteins, transport and store lipids, form lysosomes
What is endoplasmic reticulum?
- elaborate system of parallel double membranes forming flattened sacs with fluid filled spaces called cisternae
- RER connected to nuclear envelope
What is RER and its role?
- ER with ribosomes on surface (site of protein synthesis)
- isolate and transport proteins made in the ribosome
What is SER and its role?
- no ribosomes
- more tubular
- synthesis and transport of lipids and steroids
What is the nucleus and nucleolus? What are their roles?
- spherical, 10-20um in diameter
- bounded by 2 membranes called the nuclear envelope which has pores to allow mRNA and ribosomes to exist their site of synthesis and go to the cytoplasm
- nucleoplasm contains chromatin (coils of DNA bound to protein)
-nucleolus is the site of formation of rRNA
What is mitochondria? What’s its role?
- double membrane bound organelle
- produce ATP energy via respiration
- organic matrix containing lipids and proteins and cristae which provide SA for enzymes involved in AR
- large surface area to volume ratio = efficiency
- 70S ribosomes allow protein synthesis
- small amounts of DNA
What are ribosomes and their role?
- assembled in nucleus from rRNA and protein
- sit of translation of the genetic code
- 2 sub units for tRNA and mRNA attachment
- assemble proteins
Chloroplasts and their role
- photosynthesising tissue
- 2 membranes: chloroplast envelope
- stroma fluid, able to replicate
- thylakoids are flattened sacks that stack to from granum (chlorophyll found here)
What are centrioles and their role?
- star shaped tubes found outside the nucleus
- not in higher cells of plants
- synthesise microtubules of the spindle in CD
What are lysosomes?
- small, temporary vacuoles surrounded by a single membrane formed by being pinched off the Golgi body
- contain and isolate digestive enzymes and fuse and digest worn out cell parts
- digest materials engulfed by cell (ie bacteria)
Structure of the cell wall
- cellulose
- held together in microfibrils, aggregated to fibres and embedded in a polysaccharide matrix called pectin
Outline the functions of the cell wall
- transport: the gaps between fibres make cell wall fully permeable to water and dissolved molecules/ions. Called apoplast and is main pathway for water
- mechanical strength: strong and resists expansion when vacuole is full, making cell turgid and supportive
- communication: cell walls have pores through which strands of cytoplasm called plasmodesmata pass ( cytoplasmic connections between adjacent plant cells). Occurs where there is no cellulose thickening
Explain division of labour in creation of proteins/enzymes
- nucleus contains chromosomes in which the DNA encodes protein
- nuclear pores in the nuclear envelope allow mRNA molecules transcribed off the DNA to leave the nucleus and attach to ribosomes in RER
- ribosomes contain rRNA transcribed from DNA in nucleolus
- protein synthesis occurs on ribosomes - primary structure
- polypeptides transported through RER and packaged into vesicles. Bud off and carry to Golgi body to be chemically modified and folded
- Golgi body produces vesicles w newly synthesised proteins - lysosomes or secretary vesicles for exocytosis
What are viruses?
- acellular organisms
- no organelles, cytoplasm or chromosomes
- exist as inert ‘virions’ until in a host cell which they take over and multiply
- core of nucleic acid (RNA or DNA), surrounded by a protein coat called the capsid
What are the viruses that attack bacteria?
- bacteriophage
- ie T2 which attacks E. coli
Define differentiation and explain how it occurs
- the development of a cell into a specific type
- turn genes on and off
- unspecialised cells are called ‘packing cells’
What is epithelial tissue?
- tissue that covers and lines the internal and external surfaces of the body
- no blood vessels but can have nerve endings
- sit on a basement membrane made of collagen and protein
- usually a secretory or protective function
What is cuboidal epithelial tissue?
- simplest form
- 1 cell thick
- on the proximal convoluted tubule of the kidney nephron and ducts of the salivary glands
What is columnar epithelial tissue?
- also known as ciliated
- elongated cells that line the tubes substances move through (oviduct of Fallopian tubes and trachea)
- cilia on end beat
What is squamous epithelium tissue?
- flattened cells
- walls of alveoli and lime the renal capsule of the nephron
Describe skeletal muscle tissue
- attached to bones and generates locomotion on mammals
- bands of long cell fibres
- tires easily
- has voluntary muscles
—> is striped
Describe smooth muscle
- spindle shaped that contract rhythmically
- skin, blood vessels, digestive & respiratory tracts
- involuntary muscles
—> not striped
Describe cardiac tissue
- mix of smooth and skeletal - striped but lacks the long fibres
- contracts rhythmically
- does not tire
What is connective tissues?
- connects, supports or separates tissues and organs
- elastic and collagen fibres in extra cellular fluid or matrix
- fat cells (adipocytes) between fibres
What is chromatin?
Coils of DNA bound to histone proteins
2 differences between ribosomes in animal cells and ribosomes in prokaryotic
- animals are 80S and prokaryotic are 70S
- ribosomes not attached to ER in the prokaryotes
Why do some mitochondria appear different to each other?
Cut in a different plane or angle
2 structures found in prokaryotic cells also found in mitochondria
- loop of DNA
- 70S ribosomes
- both have plasma cell membranes
Describe two differences between mitochondria and prokaryotic cells
- mitochondria has double membrane, no cell wall, no mesosomes and no flagellum
