Cells Flashcards
What is cell fractionation?
Process where cells are broken up and organelles are separated out of the cell
What are the conditions needed for cell fractionation to take place?
- Cold: to rescue enzyme activity that could break down organelles
- Same water potential as the solution: to prevent organelles from bursting/shrinking due to osmosis
- Buffered: so pH does not change which could change the structure of organelles/functioning of enzymes
What are the steps of cell fractionation?
- Homogenisation: Breaks up plasma membrane and releases organelles
- Filtration: Solution is filtered through a gauze which separates large cell debris from organelles. As organelles are smaller than the debris, they pass through the gauze.
- Centrifugation: Centrifugal force causes the most dense organelles to form a pellet at the bottom of the tube. Speed increases to remove the supernatant and leave pellets behind
What is the order of organelle size?
Largest: Nucleus Chloroplast Mitochondria Lysosome Rough Endoplasmic reticulum Ribosomes Smallest
What is the equation for magnification?
Image size / actual size
What is resolution and magnification?
Resolution -resolving power- ability to distinguish between two objects
Magnification- How many times bigger the image is compared to the actual object
What are the comparisons between electron and light microscopes?
Electron microscopes have a short wavelength compared to light therefore a higher resolving power
Electrons are negatively charged so beam can be focused using electromagnets
Electron microscopes have a higher magnification
Light microscopes can be used to view living things whereas optical cant
Light microscopes are cheaper/easier to use compared to electron
Electron microscopes have to be in a vacuum, light microscopes do not
What is the max magnification and revolution of a light microscope?
x1500 + 200nm
What is the max magnification and revolution of an electron microscope?
x1500000 + 0.1-0.2nm
What are the differences between SEM and TEM?
TEM
Beam passes through specimen
Produces 2D image
SEM
Beam is on the surface of the specimen from above
Produces a 3D image
Lower resolution than TEM
What is an eyepiece graticule?
Glass disk placed in the lens of microscope which has as scale on - usually 10mm long and has 100 sub divisions
What needs to be done before using an eyepiece graticule? + how is this done?
Calibrated for a particular lens:
Using a stage micrometer (special slide), this is usually 2mm long and has small division of 0.01 mm
Eyepiece graticule and micrometer need to be lined up to calculate the length of the divisions on the eyepiece graticule
What is the structure of the nucleus?
Nuclear envelope: Double membrane which controls the entry/exit of materials in the nucleus and the reactions
Nuclear pores: Allow the passage of large molecules like mRNA
Nucleolus: creates rRNA + assembles ribosomes
Chromosomes: contains protein bound, linear DNA
What is the function of the nucleus?
Controls all activities in the cell
Produces mRNA and tRNA for protein synthesis
Contains DNA
Produces rRNA + ribosomes
What is the function of the mitochondria?
Produces ATP and transfers energy from respiration
What is the structure of mitochondria?
Double membrane- inner membrane is invaginated which forms cristae
Cristae- gives a large surface area for respiration
Matrix- contains proteins, lipids, ribosomes, DNA to control production of proteins
What is the function of chloroplasts?
Carry out photosynthesis
What is the structure of chloroplasts?
Double membrane
Grana- stacks of disc like structures called thylakoids, where chlorophyll is stored
Stroma- location of starch grains and a fluid filled matrix
What is the function of rough endoplasmic reticulum?
Provides a large surface area for synthesis of glycoproteins/proteins
Provides a pathway for material transport like proteins
What is the structure of rough endoplasmic reticulum?
Has ribosomes on outer surface
What is the function of smooth endoplasmic reticulum?
Synthesises, stores and transports lipids/carbohydrates
What is the structure of smooth endoplasmic reticulum?
No ribosomes/more tubular than RER
What is the structure of Golgi apparatus?
Like a wifi sign, has many circular vesicle structures surrounding it
Has cisternae- flattened membrane sacs
What is the function of golgi apparatus?
Golgi modifies proteins by adding non-protein components like carbohydrates and these are transferred through the vesicles.
What is the structure of lysosomes?
Circular structures containing enzymes
What is the function of lysosomes?
Hydrolyse material ingested by phagocytic cells
Release enzymes outside cell for exocytosis
Digest worn out organelles to reuse their chemicals
Break down cells when they are dead -> autolysis
What is the function of ribosomes?
Site of protein synthesis
What are the two types of ribosomes and where are they found?
70s- in prokaryotes
80s- in eukaryotes
What is the structure of vacuoles?
Filled with cell cap
Single membrane (tonoplast)
Have a central vacuole inside
What is the function of vacuoles?
Make cells turgid to support plants
Can act as a temporary food store due to sugars and amino acids
What is the function of the cell wall? + what is it made of?
Made of microfibrils and cellulose
Gives strength to cell to avoid bursting under osmotic pressure
Allows water to move through the plant
What is a:
Tissue
Organ
Organ system
Tissue- group of cells with a similar function working together
Organ- group of tissues that perform a variety of functions
Organ system- Organs that work together as a single unit
What are the comparisons between eukaryotes and prokaryotes?
Prokaryotic cells:
- No nucleus, only area of DNA
- DNA not associated with proteins
- DNA may be in the forms of circular strands called plasmids
- No membrane bound organelles
- No chloroplasts
- Ribosomes are smaller
- Cell wall made of murein
- May have a capsule on outside
Eukaryotic cells:
- Distinct nucleus, with envelope
- DNA associated with proteins called histones
- No plasmids + DNA is linear
- Membrane bound organelles are present
- Chloroplasts present in plant cells
- Ribosomes are bigger
- Cell wall is mostly made of cellulose
- No capsule
What are the structures found in a bacterial cell?
Cell wall Capsule Cell-surface membrane Circular DNA Plasmid
What is the function of capsules?
Protects bacterium from other cells
What is the function of plasmids?
Contains genes that allow bacteria to survive in adverse conditions
Which one is larger? Prokaryote or Eukaryote?
Eukaryote
What is the structure of a prokaryote?
Flagellum-> for locomotion Genetic material-> large circle of DNA Cytoplasm-> contains enzymes + where chemical reactions take place Ribosomes Capsule Cell wall Cell membrane Plasmid
What are viruses?
Acellular, non living particles, smaller than bacteria
Contain nucleic acids
Can only multiply in living host cells
What is the structure of a virus?
Genetic material (RNA)
Attachment proteins on outside -> allow viruses to identify/attach to host cells
Capsid -> protein coat which encloses nucleic acid
Lipid envelope
Matrix
Reverse transcriptase (enzyme)
What is mitosis?
Cell division that results in two identical daughter cells with the same DNA as parent cell
What are the 4 phases of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens in prophase?
Chromatids become visible, nucleolus disappears
Centrioles separate to opposite poles of the cell + create spindle fibres
What happens in metaphase?
Chromosomes line up along the equator of the cell
Spindle fibres released from the poles and attach to the centromere/chromatid
What happens in anaphase?
Spindle fibres retract which pulls centromere/chromatids which are bound to opposite poles
Therefore centromere divides in two and chromatids are pulled to opposite poles
Separated chromatids = chromosomes
Requires ATP from respiration
What happens in telophase?
Chromosomes become longer and thinner
Spindle fibres disintegrate but nucleus forms again
Cytoplasm splits in two to create two identical cells
What is a centromere?
The centre of a chromosome
What is cytokinesis?
Cytoplasm splits in two to create two identical cells
What is the process of cell division in prokaryotic cells?
Binary fission:
Circular DNA replicates and these attach to cell membrane
Plasmids replicate
Cell membrane grows bigger and cytoplasm divides into two
New cell wall forms between DNA molecules which divides the original cell into two identical daughter cells
(this contains circular DNA + copies of plasmids)
How do viruses undergo cell division?
They cannot undergo cell division therefore they replicate by attaching to a host cell through their attachment proteins + inject their nucleic acid into the host cell which gives the ‘instructions’ to form new viruses
What part of the cell cycle does DNA replication occur?
Interphase
What occurs when there is uncontrolled cell division?
Tumours and cancer
What are the 3 stages of the cell cycle?
Interphase
Nucelar division -> mitosis
Cytokinesis
How long is the cell cycle/longest stage?
Usually around 24 hours and interphase is 90% of this time
How is cancer treated?
Killing dividing cells by blocking a part of the cell cycle:
-preventing DNA from replicating
-inhibiting metaphase stage of mitosis by interfering with spindle formation
BUT these also interfere with normal cells which divide rapidly which is why hair loss occurs in cancer treatment
