Chapter 2 Basic Components of Living Systems Flashcards by Zoha Riaz

What is cell theory?

both plants and animal tissue is composed of cells
cells are the basic unit of all life
cells only develop from existing cells

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Describe how a compound light microscope works?

A compound light microscope has two lenses…

OBJECTIVE : placed near the specimen (produces a magnified image)

EYEPIECE : through which the specimen is viewed (magnifies the image again)

the objective/eyepiece lens configuration allows for much higher magnification and reduced chromatic aberration than that in a simple light microscope

ILLUMINATION provided by a light below the specimen (sometimes also above)

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What are the 4 ways to prep a sample?

(1) Dry mount

(2) Wet mount

(3) Squash slides

(4) Smear slides

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(1) Dry mount??

Solid specimens are viewed whole/cut into very thin slices with a sharp blade (sectioning).

Specimen is placed on the centre of the slide, and a coverslip is placed over the sample.

e.g. hair, pollen, dust can be viewed this way

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(2) Wet mount??

Specimens are suspended in a liquid : water OR immersion oil.

Coverslip is placed on from an angle (to prevent air bubbles forming).

e.g. aquatic samples and living organisms can be viewed this way

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(3) Squash slides??

First prepare a wet mount, then use a lens tissue to gently press down the cover slip.

Good technique for soft samples.

e.g. root tip squashes can be viewed this way (cell division)

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(4) Smear slides??

The edge of a slide is used to smear the sample, creating a thin, even coating on another slide.

e.g. samples of blood can be viewed in this way (cells)

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Name 2 POSITIVELY charged dyes?

Crystal violet

Methylene blue

(attracted to negatively charged materials in the cytoplasm = staining of cell components)

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Name 2 NEGATIVELY charged dyes?

Nigrosin

Congo red

REPELLED by negatively charged cytosol = leaves cells UNSTAINED (stay on the outside cells)
- therefore stand out against stained background

= NEGATIVE STAINING TECHNIQUE

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What is differential staining?

Used to distinguish between 2 types of organisms / 2 organelles (in a single organism) that would otherwise be hard to identify.

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What is gram stain technique?

Used to separate bacteria into 2 groups : GRAM + and GRAM -

(1) Apply crystal violet to a bacterial specimen.
(2) Then apply iodine, which FIXES the dye.

(3) Wash the slide with alcohol.
- Gram + bacteria will RETAIN the crystal violet dye.
- Gram - bacteria have THINNER cell walls and therefore do NOT retain the crystal violet dye.

(4) Gram - bacteria is stained with SAFRANIN dye = counterstain

Gram + bacteria = blue/purple
Gram - bacteria = red

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What is the difference between Gram + and Gram - bacteria?

Gram + bacteria are susceptible to the antibiotic penicillin (which inhibits the formation of cell walls).

Gram - bacteria have much thinner cell walls that are not susceptible to penicillin.

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What is the acid-fast technique?

Used to differentiate species of Mycobacterium from other bacteria.

(1) Lipid solvent is used to carry carbolfuchsin dye into the cells.

(2) Wash the cells with a dilute acid-alcohol solution.
- Mycobacterium are NOT affected by the acid-alcohol solution and therefore retain the carbolfuchsin stain = bright red.
- Other bacteria lose the stain.

(3) Apply methylene blue dye
- Other bacteria = blue

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Fixing??

When chemicals are used to preserve specimens in as near-natural a state as possible.

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Sectioning??

Specimens are dehydrated with alcohols and then placed in a mould with wax/resin = forming a hard block. This block can then be sliced thinly using a MICROTOME (knife).

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Staining??

Specimens are often treated with multiple stains to show different structures.

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Mounting??

Specimens are then secured to a microscope slide with a coverslip placed on top.

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What is the definition of magnification?

How many time larger the image is than the actual size of the object being viewed.

interchangeable lens on a compound light microscope determines the amount of detail that can be seen.

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What is the definition of resolution?

The ability to see individual objects as separate entities.

the resolution of a microscope determines the amount of detail that can be seen.

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What is resolution limited by?

Diffraction of light as it passes through samples (and lenses).

DIFFRACTION = tendency of light waves to spread as they pass close to physical structures

The physical structures present in specimens are close together and the light reflected from individual structures can OVERLAP due to diffraction.
= structures are no longer seen as separate entities
= detail is lost

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How can you increase resolution?

By using beams of electrons which have a wavelength shorter than that of light, meaning that individual beams can be much closer before they overlap.

= objects which are much smaller and closer together can be seen separately without diffraction blurring the image.

Calculation for magnification?

M = I ÷ A

M = magnification
I = image size
A = actual size

(CAN BE REARRANGED)

How do you calibrate a light microscope using a graticule?

What is electron microscopy?

When a beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen.
- more detail of cell infrastructure can be seen as electrons have a much smaller wavelength than light waves.

= up to x 500 000 magnification with clear resolution

What are the disadvantages of electron microscopy?

very expensive
can only be used inside a carefully controlled environment in a dedicated space
specimens can be damaged by the electron beam
therefore complex prep process
ARTEFACTS (structures that are produced due to the prep process)

Two types of electron microscope?

TEM (transmission electron microscope)
SEM (scanning electron microscope)

TEM?? (What is the resolving power?)

A beam of electrons is transmitted through a specimen and focused to produce an image - (similar to light microscopy).

BEST resolution achieved = 0.5nm

SEM?? (What is the resolving power?)

A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected.

resolving power = 3-10 nm

What is an artefact?

A visible structural detail caused by the processing of the specimen and NOT an ACTUAL FEATURE of the specimen.

air bubbles
loss of continuity in cell membranes
distortion of organelles
empty spaces in cytoplasm of cells

LSCM??

LASER SCANNING CONFOCAL MICROSCOPY

In fluorescent microscopes a higher light intensity is used to illuminate a specimen that has been treated with a fluorescent dye.

FLUORESCENCE = the absorption and re-radiation of light
- light of a LONGER WAVELENGTH and LOWER energy is emitted = MAGNIFIED image

LSCM moves a single spot of focused light across a specimen.

Emitted light if FILTERED through a pinhole aperture (only light radiated from very close to the focal plane is detected).

Any light emitted from other parts of the specimen = DECREASES resolution and causes blurring (therefore does not pass through the pinhole aperture and is not detected)

Benefits of LSCM?

Laser used instead of light results in HIGEHR INTENSITIES which improves ILLUMINATION.

As very thin sections of specimen are examined and light from elsewhere is removed = HIGH RESOLUTION images can be produced.

2D image (moving spot across specimen)
3D image (creating images at different FOCAL PLANES)

NON-INVASIVE

Explain the beamsplitter of a LSCM?

= DICHROIC mirror

Which only reflects one wavelength from the mirror but allows other wavelengths produced by the sample to pass through (to the pinhole aperture)

What are the 2 fundamental types of cell?

EUKARYOTIC (make up multi-cellular organisms)
PROKARYOTIC (single called organisms)

Nucleus??

Contains coded genetic info in the form of DNA molecules.
- DNA directs the synthesis of all proteins required by the cell
- controls the metabolic activity of the cell

DNA is contained within a double membrane = NUCLEAR ENVELOPE (protects it from damage in the cytoplasm)

NUCLEAR ENVELOPE contains NUCLEAR PORES that allow molecules to move in and out of the nucleus

DNA associates with proteins called HISTONES to form CHROMATIN. Chromatin coils and condenses to form chromosomes (these only become visible during mitosis).

Nucleolus??

Area within the nucleus responsible for producing RIBOSOMES.

= composed of proteins and RNA

RNA produces —> rRNA (ribosomal RNA)
rRNA + proteins —> RIBOSOMES

Mitochondria??

Essential organelles.

= site of final stages of cellular respiration, where the energy stored in the bonds of complex, organic molecules is made available for the cell to use by the production of ATP

DOUBLE MEMBRANE

highly folded INNER membrane = CRISTAE
fluid inside = MATRIX

Contain a small amount of DNA, mitochondrial (mt) DNA.
- can produce their own enzymes
- can reproduce themselves

Vesicles and Lysosomes??

VESICLES are membranous sacs that have storage and transport roles.
- consist of single membrane with fluid inside

LYSOSOMES are specialised forms of vesicles.
- contain HYDROLYTIC ENZYMES
- responsible for breaking down waste material in cells (old organelles)

in the immune system, responsible for breaking down pathogens ingested by phagocytic cells
important role in programmed cell death (G0) - apoptosis

Cytoskeleton??

Network of fibres necessary for the shape and stability of a cell.

Organelles are HELD IN PLACE by the cytoskeleton and it controls cell movement and the movement of organelles within the cell.

(1) MICROFILAMENTS
- contractile fibres (formed from actin)
- cell movement
- cell contraction (cytokineses)

(2) MICROTUBULES
- globular tubulin proteins polymerise = tubes
- scaffold-like structure determines shape of cell
- act as tracks for the movement of organelles
- spindle fibres are composed of microtubules

(3) INTERMEDIATE FIBRES
- provide mechanical strength to cells
- help maintain integrity

Centrioles??

Composed of microtubules.

2 associated centrioles = centrosome (involved in the organisation and assembly of spindle fibres in cell division)

Flagella and Cilia??

Hair-like structures which protrude from cells.

Flagella used primarily to enable cells MOTILITY or as a sensory organelle.

Cilia can be mobile/stationary.
- stationary cilia are present on the surface of many cells and have an important function in sensory organs

mobile cilia beat in a rhythmic manner = current formed = adjacent fluids/objects to the cells are moved

Each CILIUM contains 2 central microtubules surrounded by 9 pairs of microtubules = 9 + 2 arrangement
- pairs of parallel microtubules slide over one another causing the cilia to move in a beating motion

Endoplasmic reticulum??

ER is a network of membranes enclosing flattened sacs called CISTERNAE.

Connected to the outer membrane of the nucleus.

SMOOTH ER is responsible for lipid and carb synthesis and storage.

ROUGH ER has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins.

Ribosomes??

Free-floating in the cytoplasm OR attached to the RER.

Not surrounded by a membrane.

Constructed of RNA molecules made in the nucleolus of the cell.

SITE OF PROTEIN SYNTHESIS.

Golgi apparatus??

Similar on structure to SER.

Compact structure formed of cisternae and does not contain ribosomes.

Role of modifying proteins and packaging them into (SECRETORY) VESICLES.

Steps of protein production??

1) Proteins are synthesis on the ribosomes bound to the ER.

2) They then pass into the cisternae of the ER and are packaged into transport vesicles.

3) Newly synthesised proteins in transport vesicles move towards Golgi apparatus VIA CYTOSKELETON.

4) Vesicles fuse with the CIS face of the Golgi apparatus and the proteins enter.

5) The proteins are structurally modified and packaged into vesicles. Leave via the TRANS face of the Golgi apparatus.

6) Secretory vesicles carry the proteins that are to be released from the cell. Contents released by EXOCYTOSIS.
- some vesicles form lysosomes - these contain enzymes for use in the cell

What are plant cell walls made up of?

CELLULOSE (complex carb)

freely permeable
gives cell shape
contents of the cell press against cell = rigid
defence mechanism from invading pathogens

Vacuoles??

Membrane lined sacs in the cytoplasm containing CELL SAP.

permanent vacuoles important in maintaining turgor - rigidity
membrane = TONOPLAST (selectively permeable)

(In animals, vacuoles are small and transient).

Chloroplasts??

Organelles responsible for photosynthesis.

DOUBLE MEMBRANE structure like mitochondria.
- fluid = STROMA
- internal network of fibres which form flattened sacs = THYLAKOIDS

several THYLAKOIDS stacked together = GRANUM (joined by lamellae)

GRANA contain CHLOROPHYLL

contain DNA and ribosomes
LARGE SA (internal membranes)

DNA in prokaryotes??

Generally 1 molecule of DNA (chromosome) supercoiled - compact.

PLASMIDS

Ribosomes in prokaryotes??

SMALLER than those in eukaryotes.

80s vs. 70s

Still responsible for protein synthesis

Cell wall??

Made of PEPTIDOGLYCAN (complex polymer of amino acids and sugars)

Flagella in prokaryotes??

Thinner and does not have the 9 + 2 arrangement.

Energy used to rotate supplied by CHEMIOSMOSIS not ATP

attached to the cell membrane of cell by a ‘basal body’ and rotated by molecular motor.

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Chapter 2 Basic Components of Living Systems Flashcards

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