Cell structure Flashcards
What is a eukaryotic cell?
Cell where the DNA is contained in nucleus and membrane-bound organelles
What is a prokaryotic cell?
DNA is free in cytoplasm and no organelles
Describe the structure of nucleus
- Nuclear envelope: Double membrane controls what enters and exits
- Nuclear pores: Allows large molecules out
- Nucleolus: Small sphere makes rRNA/ribosomes
- Nucleoplasm: Granular jelly-like material fills nucleus space
- Chromosomes: Protein bond linear DNA
Function of nucleus
- Site of DNA replication
- Site of mRNA/tRNA/rRNA/ribosome production
- Contains genetic material of cell
Describe the structure of mitochondria
- Double membrane: Controls entry and exit
- Cristae: Extension of inner membrane = large SA for respiration enzymes
- Matrix: Respiratory enzymes + proteins + lipids
- Mitochondrial DNA: Loop of DNA to produce own proteins
Function of mitochondria
- Site of aerobic respiration
- Site of production of ATP
- DNA codes for enzymes needed in respiration
Describe the structure of chloroplast
- Double membrane: Controls entry and exit
- Thylakoid: Folded membrane disks containing chlorophyll stack up to make grana
- Grana: Large surface area for chlorophyll + proteins for LDR
- Lamellae: Tubular extensions that attach thylakoids to adjacent grana
- Stroma: Fluid filled matrix with enzymes for LIR
- DNA/Ribosomes: To produce own proteins
Function of chloroplast
- Site for photosynthesis
Describe structure of endoplasmic reticulum
- Cisternae: Tubules and flattened sacs from cell membrane and connected to nuclear envelope
RER: - Ribosomes attached for large SA for protein synthesis
SER: - No ribosomes and more tubular structure
Function of endoplasmic reticulum
RER:
- Protein synthesis
- Transport of protein
SER:
- Synthesis/store/transport of lipids and carbs
Describe the structure of Golgi apparatus
- Cisternae: Stack of membrane bound flattened sacks
- Secretory vesicles: Small rounded structure that pinch off membranes
Function of Golgi apparatus
- Adds carbs to proteins to make glycoproteins
- Modify/transport/store lipids
- Produce lysozomes
Describe the structure of lysozomes
Single membrane sack containing lysozyme/hydrolyzing enzymes
Function of lysozome
- Hydrolyzes phagocytic cells
- Autolysis
- Exocytosis
- Hydrolyze worn out organelles for re-use
Describe the structure of ribosomes
- Made of a small + large subunits of protein and rRNA
- 80s: Large ribosome in eukaryotic cells
- 70s: small ribosomes in prokaryotic cells, mitochondria, chloroplasts
Function of ribosomes
- Site of protein synthesis
Describe structure of cell wall
- Plants: Made of cellulose
- Fungi: Made of chitin
- Bacteria: Made of murein
Function of cell wall
- Gives cell mechanical strength so it doesn’t burst under pressure during osmosis
- Barrier
- Structural support
Describe structure of vacuole
- Tonoplast: single membrane
- Cell sap: filled with fluid that contains mineral salts, aminos, wastes, pigments
Function of vacuole
- Turgidity to cell
- Temporary store of sugars and aminos
- Pigments cause petal color which attract pollinators
Difference between prokaryotic cells and eukaryotic cells
- Unicellular
- No membrane bound organelles
- 70S ribosomes
- No nucleus but circular free floating DNA not associated with proteins
- Murein cell walls
- Has plasmid, capsule, flagellum
Structure + function of plasmids
- Small ring of DNA
- Carries non-essential genes
Function of flagellum
- Rotating tail for mobility
Structure + function of capsule
- Slimy top coat made of proteins
- Prevents desiccation
- Protection from host immunity
Describe the structure of a viral particle
- Linear genetic material
- Viral enzymes
- Protein capsid
IF ENVELOPED VIRUS: - Lipid envelope
- Attachment proteins
Describe how optical microscopes work
- Beam of light condensed to create image
- Different structures absorb different amounts/wavelengths of light
- Reflected light transmitted to observers eye
Describe how electron microscopes work
- Beam of electrons is condensed by electromagnets in a vacuum chamber
- High energy beam passes through/over specimen
- Denser areas absorb more electrons
- Focus image onto fluorescent screen which will produce image on computer
Pros/Cons of optical microscope
PROS:
- Affordable
- Colored image
- Living specimen
CONS:
- Lower magnification
- Lower resolution as light has a longer wavelength
- 2D
- Can’t see organelles
Pros/Cons of TEM
PROS:
- High magnification
- High resolution as electrons have a shorter wavelength
- Detailed imaging of organelles + internal structures
CONS:
- Expensive
- BW imaging
- 2D
- Vacuum = non-living specimen
- Artefacts
- Must be a thin sample
Pros/Cons of SEM
PROS:
- High resolution as electrons have a shorter wavelength
- Detailed image of 3D structure cells
- Specimen doesn’t need to be thin
CONS:
- Expensive
- BW imaging
- Vacuum = non- living specimen
- Only shows outer surface
Formula for magnification
M= I/A
IF SCALE BAR:
Measurement mentioned on scale bar = actual size
Measurement taken of scale bar = image size
What is magnification?
Factor by which the image is larger than the actual specimen
What is resolution?
Minimum distance at which 2 structures can be distinguished
Describe how to calibrate an eye piece graticule
1) Put stage micrometer onto stage and line up with graticule values
2) Count how many divisions on the graticule fit in 1 division on the micrometer
3) Length of 1 graticule division= measurement of 1 division on micrometer/ number of divisions
4) Calibrated values can be used to measure actual size
Describe cell fractionation
1) Homogenize tissue to break open cells to release the organelles
2) Filter homogenate to remove large cell debris
3) Spin homogenate in centrifuge
4) Most dense organelles will form pellet at the bottom
5) Filter off supernatant and spin again at higher speed
Order of pellets formed in ultracentrifugation
- Nucleus
- Chloroplast
- Mitochondria
- Lysozomes
- ER
- Ribosomes
Why must the solution be cold + isotonic + buffered?
- Cold: Reduce enzyme activity that could damage organelles
- Isotonic: Same water potential so organelles don’t burst/shrivel
- Buffered: Constant pH not to damage organelles
Stages of the cell cycle
- Interphase: Longest stage of growth + synthesis
- Nuclear division: Mitosis/meiosis
- Cytokinesis: Division of cytoplasm
Stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Describe prophase
- Chromosomes condense and become visible
- In animal cells centrioles move to opposite poles of cell
- Nuclear envelope + nucleolus disintegrate
Describe metaphase
- Sister chromatids line at equator
- Spindle fibers attach to centromeres
Describe anaphase
- Using energy from ATP spindle fibers retract = centromere splits
- Sister chromatids separate into 2 chromosomes and are pulled to opposite poles
- Spindle fiber disintegrates
Describe telophase
- Chromosomes become thin + long
- Nuclear envelope starts to reform
Describe cytokinesis
- Cytoplasm splits into 2 = 2 new genetically identical cells
Purpose of mitosis
- Cell replacement/repair
- Growth
- Asexual reproduction
Formula to calculate mitotic index
MI = Number of cells in mitosis/ Total cells *100
Describe binary fission
-DNA loop replicates + both copies stay attached to cell membrane + plasmids replicate in cytoplasm
- Cell elongates, separating the 2 DNA loops
- Cell membrane contracts & septum forms
- Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids
