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Biology > Microscopes and cell structure > Flashcards

Microscopes and cell structure Flashcards

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1
Q

Magnification

A

The number of times larger an image appears , compared with the real size of the object.

magnification = image size / size of real object

Using a scale bar:
-measure the length of the scale bar(mm)
- measure the diameter of the structure (mm)
-length of structure/length of scale bar
-multiply by value shown on the scale bar

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2
Q

Resolution

A

The clarity of an image , the ability to distinguish two separate points .It allows more detail to be seen.

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3
Q

electron micrograph & photomicrograph

A

Photograph of an image seen using an electron microscope.

Photograph of an image seen using an optical microscope

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4
Q

Light (optical) microscope

A
  • lenses focuses the rays of light and magnify the view of the thin slice of specimen
  • different structures absorb different amounts of wavelength of light.
  • Reflected light is reflected back to the observer via the objective and eyepiece lenses.

-can use living cells

Magnification ~ x1500-x2000
Resolution ~ 200nm(limited by the wavelength of light)
produces a photomicrograph

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5
Q

Transmission electron microscope (TEM)

A
  • A high energy beam of electrons are passed through a thin slice of specimen
  • the denser the structure the darker it appears as it absorbs more electrons
  • focuses image onto a fluorescent screen or photographic plate to produce and black and white 2D image.
  • requires a thin slice of specimen

Magnification ~ x 50 million
Resolution ~ 0.05 - 2nm

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6
Q

Scanning electron microscope (SEM)

A
  • Focus a beam of electrons onto the specimen using electromagnetic lenses.
  • secondary electrons bounce off and are detected and focused onto a screen.
  • image is in black and white but false colour can be added.
  • specimen must be placed in a vacuum and coated in precious metals.
  • magnification~ x200,000
    -resolution ~ 5-50nm
  • 3D image
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7
Q

Laser Scanning confocal microscopes

A
  • most modern technique
  • uses laser light to illuminate the specimen and LIVE samples can be viewed.
  • can visualise specific proteins and structures and watch them move.
  • allow us to tag these with special dyes and antibodies.
  • resolution ~200nm
  • coloured
  • 2D image (many planes of focus can be combined in a computer to construct a 3D image.
  • cross section of the specimen can be seen by adjusting the plane of focus at different horizontal levels.
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8
Q

Electron microscopes

A

-electrons have a short wavelength meaning they have a higher resolution

-electron microscopes contain a vacuum so electrons can passthrough without bouncing off molecules in the air.

  • resolution is 2000x better than light microscopes
  • cannot view living specimen
  1. a beam of electrons pass down the microscope.
  2. focus the electron beam by using electromagnets called electromagnetic lenses.
    3.specimen placed in the path of the electron beam
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9
Q

Stains

A
  • allows us to contrast different structures
  • makes the internal structures more visible
  • creates a clearer image
  • differential staining ~ use two different coloured stains simultaneously on the same specimen.
  • do not use stains on LIVE specimen ~ instead we use light interference which shows an illuminated specimen against a dark background.

Examples:

iodine ~ cellulose in cell walls (yellow)
sudan red ~ lipids
crystal violet ~ groups of bacteria
acetic orcein ~ binds to DNA and stains chromosomes dark red.

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10
Q

eye piece graticule

A
  • A measuring device.
  • placed in the eyepiece of a microscope
  • acts as a ruler when you view an object under the microscope
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11
Q

stage micrometer

A
  • A precise measuring device
  • placed on the stage
  • used to calibrate the value of eyepiece divisions at different magnifications.
  • 1mm in length (1000 micrometres)
  • 100 divisions ( each 10 micrometres in length)
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12
Q

calculation method using graticules:

A
  1. find a length on the stage micrometer than aligns with a length on the eyepiece graticule.
  2. stage micrometer / eyepiece graticule
    This tells us the length of one unit at that magnification
  3. measure the object in graticule units
  4. value from step 3 x length of one unit (step 4) = actual object length
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13
Q

objective & value of one eyepiece division

A

x4 ~ 25
x10 ~ 10
x40 ~ 2.5
x100 ~ 1.0

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14
Q

Proteins and protein synthesis

A

Enzymes ~chemical reactions
Structural proteins ~ e.g organelle movement
Transport molecules ~ e.g haemoglobin

Protein synthesis:
The instructions for encoding an amino acid sequence of a protein are contained within the gene for that protein.

TRANSCRIPTION ~ the genetic information encoded by that gene is converted into mRNA.

TRANSLATION ~ mRNA leaves the nucleus and a ribosome reads the information contained in the mRNA and synthesises the protein molecule.

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15
Q

Proteins that remain in cytoplasm
VS
proteins secreted by cells

A

Translation takes place on a free ribosome in the cytoplasm . example ~ cellular enzyme.

Translation takes place on a ribosome attached to the RER and makes its way through the RER and the golgi apparatus.

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16
Q

Nucleus

A

Houses nearly all the cells genetic material.

STRUCTURE:
- Double membrane ( nuclear envelope) ~ contain nuclear pores which allow molecules to enter and leave the nucleus.
ENTER ~ steroid hormones
LEAVE ~ rRNA

  • Chromatin ~ consists of DNA coiled around proteins called histones .
    The DNA and histone proteins form chromosomes which are only visible unless cell has undergone mitosis or meiosis.
  • Nucleolus ~ No membrane, produces ribosomal RNA (rRNA).Form part of the structure of ribosomes.
17
Q

Rough endoplasmic reticulum (RER)

A

The intracellular transport system ~ the cisternae form channels for transporting substances from one area of the cell to another.

STRUCTURE:
- sheets of membranes forming flattened sacs called cisternae which contain enzymes.

  • membranes of the cisternae are covered with ribosomes.
  • Ribosomes is where translation takes place for proteins which are secreted from the cell.
  • these proteins actively pass through the membrane into the cisternae and are transported to the golgi apparatus for modification and packaging.
18
Q

Smooth endoplasmic reticulum (SER)

A

STRUCTURE:
- a system of membranes forming cisternae

  • no ribosomes on its surface.
  • make and store lipids and carbohydrates that can then be passed through the golgi apparatus to be modified.
19
Q

Golgi apparatus

A
  • consist of sheets of flattened sacs called cisternae.
  • have secretory vesicles which bring material to and from the golgi apparatus.

Modify proteins :
- add sugar molecules ~ glycoproteins
- add lipid molecules ~ lipoproteins
- fold into 3D shape

Package proteins:
- stored in the cell
OR
- moved to the plasma membrane to be either incorporated or exported.

20
Q

Mitochondria

A
  • Produce the energy carrying molecule , ATP, for aerobic respiration
  • Double membrane (inner & outer) with a fluid filled space between them.
  • The inner membrane is highly folded into CRISTAE which increases the SA for enzymes.
  • inner part is a fluid filled MATRIX

-Loop of DNA ~ contain the genes required for some of the enzymes involved in aerobic respiration.

  • Ribosomes ~ synthesise the proteins encoded by the mitochondrial DNA.
21
Q

Lysosomes

A
  • from the golgi apparatus , a number of proteins are packaged into vesicles which go on to form lysosomes.
  • single membrane
  • Powerful hydrolytic (digestive) enzymes ~ digest large molecules into smaller soluble molecules.
  • internal fluid ~ acidic as this the optimum PH for lysosmal enzymes.
  • Key role in phagocytosis . example ~ in white blood cells.
  • destroy organelles that are damaged or no longer functional.
22
Q

Chloroplasts

A

Function ~ where photosynthesis takes place.
Large organelles ~ 4-10 nanometres long.

Structure:

DOUBLE MEMBRANE ~ control which molecules enter and leave the chloroplast.

THYLAKOIDS~
- membrane - bound discs
-where light DEPENDENT reactions take place.
- contain the chlorophyll and enzymes needed for the light dependent reactions.

GRANUM~ formed by thylakoids stacked on top of each other , so light can be absorbed more efficiently.

LAMELLAE:
- flattened discs
- connect thylakoids on different grana.
-play a role in the light dependent reactions
- allow chemicals to pass between the grana.

STROMA ~
- fluid filled matrix
- where light INDEPENDENT reactions take place
- contain enzymes needed for the light independent reactions.

GLUCOSE~ converted into polysaccharide starch which is stored int he chloroplast as starch granules.

LOOP OF DNA ~ contains the genes which encode some of the proteins needed for photosynthesis.

RIBOSOMES ~ synthesise the proteins encoded by the chloroplast DNA.

23
Q

Cytoskeleton

A
  • A complex network of protein fibres that run throughout the cytoplasm.
  • non membrane bound

Micro(actin) filaments:
- narrowest diameter
- narrow fibres containing the protein actin which contract.
- involved in cell movement.
- play a role during cell division (cytokinesis)

Intermediate fibres :
- formed from a number of different proteins.
- protect against mechanical stress.
- anchor the nucleus within the cell
- enable cell to cell signalling
- adhere to basement membrane.

Microtubules:
-greatest diameter
- formed from subunits of the protein TUBULIN
- Tubulin subunits ~ assemble to form tubulin polymers which then form hollow microtubules:
- these are involved in the movement of organelles
- form spindle fibres involved in the movement of chromosomes during mitosis and meiosis.
- determine shape of cells

24
Q

Centrioles

A
  • found in simple plants ad algae but not flowering plants or most fungi.
  • Animal cells contain a pair of centrioles which are made of microtubules.
  • The two centrioles lie at right angles to each and are found near the nucleus.
  • Pair of centrioles ~ centrosome.
  • play a role in the assembly of the spindle fibres during cell division but not essential
  • form the cilia and flagella (undulipodia)
25
Q

Cilia and flagella (undulipodia)

A

Cilia :
- hair like organelles that extend from the surface of certain cells.
- found in trachea and fallopian tube.
- some do not move.

Flagella :
- whip like organelles that are found on the surface of certain cells e.g sperm.
- moves the cell
- bigger than cilia
- usually only one.

BOTH:
Running through the centre we find nine pairs of microtubules arranged in a circle with another pair of microtubules in the centre.(9+2 structure)

Contain microtubules to allow movement.

26
Q

Cell wall

A

Gives the cell rigidity and contributes to cell shape.

Plants:
- made of the polysaccharide, cellulose
- important due to the HYDROSTATIC PRESSURE of water entering and leaving the cell for photosynthesis.
- permeable to water molecules.

MIDDLE LAMELLA ~ in between plants cells which acts as a glue and contains polysaccharides and magnesium and calcium ions.

Fungi:
- made of the polysaccharide CHITIN as well as other polysaccharides and glycoproteins.

Algae:
- contain both cellulose and glycoproteins.

27
Q

Vacuole

A
  • a membrane sac which is larger than a vesicle and can be longer lived.

Roles:
- removal of waste material
-phagocytosis

Animal cells ~ temporary

Plant cells ~ a large permanent vacuole:
TONOPLAST ~ a membrane which surrounds the vacuole and controls which chemicals enter and leave.

CELL SAP ~ fluid in the vacuole which contains dissolved sugars , mineral salts and amino acids , as well as other molecules , e.g poisonous chemicals and coloured pigment.

LOW WATER POTENTIAL ~creates a hydrostatic pressure acting outwards causing the cytoplasm to press against the cellulose cell wall making it turgid, which helps support the plant , especially those without a woody stem.

28
Q

Ribosomes

A
  • non-membrane bound organelles.
  • formed from rRNA in the nucleolus as two separate subunits , which pass through the nuclear envelope into the cytoplasm then combine.
  • Some remain free and some attach to the RER.
  • synthesise proteins

eukaryotes ~ size 80 s
prokaryotes ~ 70 s

29
Q

vesicles

A
  • sacs of fluid enclosed by a membrane
  • transfer material

examples:
- transfer proteins from the RER to the golgi apparatus

  • carry the glycoproteins from the golgi apparatus to the cell membrane to be secreted from the cell.
30
Q

Eukaryotic cells

A

examples ~ animals , plants & fungi.

  • DNA is contained in a membrane - bound nucleus.
  • DNA is tightly wrapped around proteins called histones.
  • DNA and histone proteins form chromosomes to pack a great deal of DNA into their nucleus.
  • DNA is a LINEAR molecule ~the ends of the DNA molecule in a chromosome are not joined together to form a loop.
  • contain MEMBRANE-BOUND organelles such as golgi apparatus , ER and mitochondria.
  • RIBOSOMES 80 s (non-membrane bound) ~ larger than the ribosomes in prokaryotes.

Animal cells ~ CELL SURFACE MEMBRANE ~ controls the molecules that can pass in and out the cell.

Plants and fungi ~ CELL WALL ~ to maintain structure.

31
Q

Prokaryotic cells

A

examples ~ bacteria and archae

  • much smaller than eukaryotes
  • They have NO membrane-bound organelles at all.
  • DNA is found in cytoplasm rather than a nucleus
  • DNA is arranged into a CIRCULAR chromosome with no free ends.
  • DNA is NOT bound to histone proteins
  • sometimes contain small loops of DNA called PLASMIDS.
  • ribosomes ~ 70s
  • Cell wall ~ PEPTIDOGLYCAN

SLIME CAPSULE ~ on the outside of the cell wall to protect the bacteria from phagocytosis by white blood cells.

FLAGELLUM ~ for movement (not always)

PILI ~ fine protein strands on surface which help bacteria attach to surfaces including other bacteria.

MESOSOME ~ infoldings in the cell membrane , artefacts.

32
Q

Making and secreting a protein

A
  1. TRANSCRIPTION:
    - occurs in the nucleus
    - the gene that has encoded for the protein is transcribed into a length of RNA , called mRNA.
  2. Many copies of the mRNA are made and leave through the NUCLEAR PORES.
  3. TRANSLATION:
    At the RIBOSOMES (attached to RER) , the instructions are translated to form a chain of polypeptide ( a protein).
  4. The RER is membrane-bound so vesicles containing the polypeptide can be PINCHED off.

5.The TRANSPORT VESICLE is moved along the CYTOSKELETON to the GOLGI APPARATUS.

6.The polypeptides are modified and packaged.

  1. SECRETORY VESICLES are pinched off from the golgi apparatus and pass to the PLASMA MEMBRANE.

8.The vesicles and plasma membrane fuse, and the polypeptide is released to the outside of the cell. ( exocytosis)

33
Q

Preparing a microscope slide

A

Select thinnest slice of specimen ~ allows rays of light to pass through.

Use a sharp blade ~ to obtain a thin slice of specimen.

Wet mount ~ to prevent distortion during slicing which could lead to the presence of artefacts.

Biology (6 decks)

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