3: Cell structure Flashcards
Cell theory
- all living organisms are made up of one or more cells
- cells are the basic functional unit
- new cells are produced from pre existing cells
How far can light microscopes and electron microscopes see objects
light; long wavelength of light means can only distinguish between objects 0.2micrometres
electron; shorter wavlengths - the beam of electrons means distinguising electrons 0.1micrometres
Are micro meters (ym) or nano metres smaller (nm)
nano metres
(nm = 1x100,000,000)
(yn = 1x1,000,000)
Resolution
the minimum distance apart that objects can be to appear as separate items
Cell fractionation
the process where cells are broken up and the organelles are separated out
What conditions are needed in the solution before cell fractionation can occur?
- COLD (to reduce enzyme activity)
- the same WATER POTENTIAL as the tissue (to prevent bursting or shrinking)
- BUFFERED (so pH doesnt fluctuate)
Two stages of cell fractionation:
- Homogenation
- Ultracentrifugation
Homogenation
Cells are broken up by a homogeniser. This releases the organelles from the cell. The left over fluid is homogenate fluid which is filtered to remove any complete cells or large pieces.
Ultracentrifugation
Fragments in the filtered homogenate fluid are seperated in a centrifuge. Spins to create a centrifugal force.
- tube of filtrate placed in centifuge and spun slowly
- heaviest organelle bottom of tube
- fluid at top of tube is removed (supernatant) and transferred to diff tube to spin quickly
- next heaviest are put at bottom
- cycle continues
Negative of light microscope
poor resolution due to long wavelength of light
How does an electron microscope work by using electron beams
the electron are negatively charged so the beam can be focused using electromagnets
- electron beam has a short wavelength
two types of electron microscope
- scanning electron microscope
- transmission electron microscope
Transmission electron microscope
electron gun that produces a beam of electrons focused by a condenser electromagnet
- beam passes through thin section, appears dark if electrons absorbed, appears light if electrons pass through
- photomicrograph
Scanning electron microscope
directs a beam of electrons on surface of specimen rather than penetrating through
- beam passed back and forth by regular pattern
- 3D image by computer analysis
Limitations of TEM
- cant be living (system is in a vaccum)
- complex staining process
- must be v thin (to allow electrons to penetrate)
- flat 2D image
Limitations of SEM
- lower resolving power than TEM
- cant be living
- need to be stained
- must be thin
In a light microscope what do you use to measure the size of an object
- eyepiece graticule, must be calibrated using a stage micrometer
Parts of the nucleus
- nuclear envelope (double membrane, has ribosomes on surface)
- nuclear pores (allows passage of large molecules like messenger rna)
- nucleoplasm
- chromosomes (consists of protein bound linear DNA)
- nucleolus (small spherical region in nucleoplasm, makes ribosomal rna and ribosomes)
Functions of the nucleus
- control centre of cell (makes mrna and trna)
- retain the genetic material of the cell in dna
- manufacture ribosomal rna and ribosomes
Mitochondria
- 1-10 micrometres
- DOUBLE MEMBRANE (inner is folded to form extensions called cristae)
- CRISTAE provide a large SA for the attachment of enzymes
- rest is the MATRIX, contains proteins, lipids, enzymes and dna
Site of aerobic stages of respiration (krebs and oxidative phosphorylation) therefore make ATP so in places with high metabolic activity like epithelial and muscle cells
Chloroplast
- chloroplast envelope, a
double plasma membrane - grana are stacks of thylakoids
- in thylakoids is chlorophyll (1st part of photosynthesis)
- stroma - fluid filled matrix (2nd part)
- chloroplasts contain dna for making proteins, stroma contains enzymes to make sugar, granal membranes large SA for chlorophyll to attach
Endoplasmic reticulum
- 3D system of sheet like membranes in the cytoplasm
- ROUGH ER: ribosomes on outer surfaces of membrane. it privdes large sa for synthesis of proteins, and pathway for materials throughout cell
- SMOOTH ER: lacks ribosomes on surface, synthesise, store and transport lipids and carbohydrates
Golgi apparatus (post office)
- similar to SER but more compact
- stacks of membranes that make flattened sacs (cisternae).
- proteins and lipids produced my ER, passed through this to label them and add non protein components
- then passed into golgi vesicles, which then fuse to the cell membrane and release
Function; form lysosomes. packaging proteins and lipids into vesicles for destination
Lysosomes
special type of golgi vesicle which contain the enzyme lysozymes.
- its a membrane bound organelle
- used to digest invading cells
Ribosomes
- small cytoplasmic granules found in all cells
- 80s in eukaryotic, 90S in prokaryotic
- large sub unit and small sub unit consisting of ribosomal rna and protein
- site for protein synthesis
cell wall
(prokaryotic) - ridid outer layer made of peptidoglycan
- cellulose microfibrils
functions is to provide mechanical strength (osmotic)
Vacuole
- fluid filled sac, single membrane called the tonoplast
Viruses
a-cellular, non living structures which consist of a nucleic acid protected by a protein coat called a capsid.
- the lipid envelope/capsid contains attachment proteins
- matrix
order of cells in organisms
- cells to tissues to organs to organ systems
structure of a bacterial cell
- cell wall (physical barrier)
- capsule (protects from other cells, helps bacteria stick together for protection)
- cell membrane
- circular dna (genetic info for replication
- plasmid (possess gene to aid survival)
Cell cycle
G1 = growth (interphase)
S = DNA synthesis (interphase)
G2 = growth and preparation for mitosis (interphase)
M = mitosis (cytokinesis- cytoplasm divides)
Mitosis compared to meiosis
- mitosis; 2 genetically identical daughter cells, same amount of chromosomes as the parent cell, one round of division, for growth and repair
- meiosis; 4 genetically identical daughter cells with half the number of chromosomes as parent cell
mitosis cycle
- Interphase (chromosomes are invisible, organelles double and dna is replicating)
Stage 1 = Prophase
Stage 2 = Metaphase
Stage 3 = Anaphase
Stage 4 = Telophase
Prophase
chromosomes condense and become visible. centrioles seperate and move to opposite poles of the cell. spindle fibres are created by the centiroles (spindle apparatus). nucleus disintergrates
Metaphase
chromosomes align along the equator of the cell. the spindle fibres released from the poles attach to the centromere and chromatid
Anaphase
spindle fibres retract back and break the centromere and pull the sister chromatids to the opposite poles. now called chromosomes. atp required.
Telophase
chromosomes are now at each pole of the cell and become longer and thinner again. spindle fibres disintergrate. nucleus starts to reform.
- cytokinesis = cytoplasm splits
treatment for cancer
killing diving cells by blocking a part of the cell cycle.
drugs like chemotherapy prevent dna replication and inhibit the metaphase
Cancer
group of diseases caused by a growth of disorder of cells. due to damage to the genes in the cell cycle which leads to uncontrolled growth
