2.1.1 cell structure Flashcards

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1
Q

State the types of microscopes

A

Light microscope
Electron microscope
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
Light scanning confocal microscope

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2
Q

State and describe the different ways to prepare a sample

A

Dry mount - Used with solid specimens that are either whole or sectioned (sectioning - cut into very thin slices with a sharp blade). E.g. hair, pollen, dust, and insect parts
Specimen placed centre of slide and cover slip placed on top of specimen.
Wet mount - specimen suspended in a liquid such as water or an immersion oil. Cover slip is placed at an angle. E.g. aquatic samples or other living organisms.
Squash slides - used for soft samples e.g. root tip squashes used to look at cell division. Wet mount is first prepared and then a lens tissue is used to gently press down the cover slip. Warning: damage can be done to cover slip (can break)
Smear slides - the edge of the slide is used to smear the sample across another slide creating a thin even coating. Cover slip placed over. E.g. a sample of blood.

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3
Q

Why would you stain a cell?

A

Stains increase contrast as different components within a cell take up the stains to different degrees.
The increase in contrast allows components to become visible so they can be identified.

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4
Q

Define differential staining

A

Differential staining can distinguish between two types of organisms that would otherwise be hard to identify. (can also differentiate between different organelles of a single organism)

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5
Q

State the different staining techniques

A

Negative stain technique
Gram stain technique
Acid-fast technique

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6
Q

Describe negative stain technique

A

Positively charged dyes (i.e. Crystal violet or methylene blue) are attracted to negatively charged materials in cytoplasm leading to staining of cell components.
Negatively charged dyes (i.e. nigrosin or Congo red) are repelled by the negatively charged cytosol. This means that the dye stays outside of the cell (leaving the cells unstained) causing the cells to stand out against the stained background. This technique is called a negative stain technique.

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7
Q

Describe Gram stain technique

A

A technique used to separate bacteria into two groups, Gram-positive bacteria (e.g Streptococcus pneumonae - causes pneumonia) and Gram-negative bacteria (e.g. Yersinia pestis - causes bubonic plague).

Crystal violet is first applied to a bacterial specimen, then iodine, which fixes the dye. Slide then washed with alcohol. Gram-positive bacteria retain the dye where as Gram-negative bacteria have much thinner walls and lose the stain.
Gram-negative bacteria are stained with the counterstain safranin, which makes them appear red.

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8
Q

Describe acid-fast technique

A

The technique differentiates species of Mycobacterium from other bacteria.
Heat or a lipid solvent is used to carry the first stain, carbolfuchsin, into the cells. Then the cells are washed with a dilute acid-alcohol solution. Mycobacterium species resist the effect of the acid-alcohol and retain the carbolfuchsin stain (bright red). Other bacteria lose the stain and take on the subsequent methylene blue stain (blue). Thus the acid-fast bacteria appear bright red, while the nonacid-fast bacteria appear blue when observed under oil-immersion microscopy.

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9
Q

Difference between Light, electron and confocal scanning laser microscopes

A
Light:
Magnification: x1500	
Resolution: 200nm
Cost: inexpensive 
Uses: Thin, transparent samples (living or dead); Natural colour; Simple preparation
SEM:
Magnification: x100,000	
Resolution: 0.2 -10nm
Cost: Expensive 
Uses: Specimens must be dead, dried and coated with heavy metals; Black & white; Complex preparation; Can see details inside of cells; Produces 3D images
TEM:
Magnification: x500,000	
Resolution: 0.02 -10nm
Cost: Expensive 
Uses: Specimens must be dead, dried and coated with heavy metals; Black & white; Complex preparation; Can see details of the surface of structures

CSLM:
Magnification: x2000 (can be up to x15000)
Resolution: 200nm
Cost: Expensive
Uses: Different layers at different depths; Living or dead; Distribution of molecules in cells; Laser causes chemical stain to fluoresce

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10
Q

What is the magnification formula?

A

magnification = Image size / actual size

remember acronym MIA

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11
Q

Define Resolution

A

resolution is the ability to distinguish between two separate points.

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12
Q

Define magnification

A

magnification is how much bigger the image is than the sample of the specimen

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13
Q

Converting units:

A

μm to mm:
divide by 1,000

μm to cm:
Divide by 10,000

1μm = 1,000 mm 
1cm = 10mm
1μm = 10,000 cm 
1μm = 1000 nm
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14
Q

Function and structure of Nucleus

A

contains coded genetic information in the form of DNA molecules (DNA directs synthesis of all proteins required by the cell).
DNA contained within a double membrane called a nuclear envelope which contains nuclear pores.
DNA is too large to leave the nucleus to the site of protein synthesis in the cell cytoplasm therefore it is transcribed into smaller RNA molecules.

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15
Q

Why does a nucleus have a nuclear envelope?

A

to protect it from damage in the cytoplasm

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16
Q

Why does a nucleus have nuclear pores?

A

to allow molecules to move into and out of the nucleus

17
Q

How do chromosomes form? (BASIC)

A

DNA associates with proteins called histones to form a complex called chromatin. Chromatin coils and condenses to form chromosomes.

18
Q

Function of Nucleolus

A

Area within the nucleus, composed of proteins and RNA.

Responsible for producing ribosomes.

19
Q

Function of Mitochondria

A

Site of the final stages of cellular respiration.

Mitochondria helps to produces ATP molecule from aerobic respiration.

20
Q

Structure of Mitochondria

A
  • double membrane

- inner membrane is highly folded to form structures called cristae and the fluid interior is called matrix.

21
Q

Function and structure of vesicles

A

Vesicles are used to transport materials inside the cell. ( transport or sensory vesicles).
Membranous sacs that have storage and transport roles AND consists of a single membrane with fluid inside.

22
Q

Function of Lysosomes

A

Lysosomes are specialised forms of vesicles that contain hydrolytic enzymes.
Responsible for breaking down waste material in cells and play an important role in the immune system as they are responsible for breaking down pathogens ingested by phagocytic cells.
Play an important role in programmed cell death or apoptosis.

23
Q

Function of Cytoskeleton

A

Present throughout the cytoplasm of all eukaryotic cells.
Network of fibres necessary for the shape and stability of a cells.
It also controls cell movement and movement of organelles within cells.
Cytoskeleton has 3 components:
- microfilaments
- microtubules
- intermediate fibres

24
Q

State the 3 components of the cytoskeleton

A
  • microfilaments
  • microtubules
  • intermediate fibres
25
Q

Function and structure of microfilaments

A

contractile fibres formed from the protein actin.
responsible for maintenance of cell shape (tension-bearing), changes in cell shape, muscle contraction, cell motility and cell division.

26
Q

Function and structure of microtubules

A

globular tubulin proteins polymerise to form tubes(forms a scaffold-like structure) that determines shape of cell.
responsible for maintenance of cell shape (compression-resisting), cell motility, chromosome movements in cell division, organelle movements.

27
Q

Function and structure of intermediate fibres

A

gives mechanical strength to cells and helps maintain their integrity

28
Q

Function of centrioles

A

Component of the cytoskeleton present in most eukaryotic cells, except flowering plants and most fungi.
Composed of microtubules.
Two associated centrioles = centrosome

Involved in the assembly and organisation of the spindle fibres during cell division

29
Q

Function and structure of Flagella

A

Used primarily to enable cell motility
In some cells, they are used as a sensory organelle detecting chemical changes in the cellls enviroment.
Flagella is longer than cilia, and more whip-like extensions that protrude for some cell types.

30
Q

Functions and structure of cilia

A

Stationary Cilia:
present on surface of many cells.
play an important role in sensory organs e.g. nose

Mobile Cilia:
beat in a rhythmic manner, creating a current, and cause fluids or objects adjacent to the cell to move
e.g. present in trachea to move mucus away from the lungs
each cilium contains two central microtubules surrounded by 9 pairs of microtubules arranged like a wheel, known as the 9+2 arrangement (pairs of microtubules slide over each other causing the cilia to move in a beating motion)

31
Q

State the two types of endoplasmic reticulum

A
  • Smooth endoplasmic reticulum (SER)

- Rough endoplasmic reticulum (RER)

32
Q

Structure of Endoplasmic reticulum (ER)

A

network of membranes enclosing flattened sacs called cisternae.
connected to the outer membrane of the nucleus

33
Q

Function of Smooth endoplasmic reticulum (SER)

A

responsible for lipid and carbohydrate synthesis and storage
Transport / synthesis / metabolism of fats / lipids / steroids (hormones) / carbohydrates.

34
Q

Function of Rough endoplasmic reticulum (RER)

A

has ribosomes bound to the surface

responsible for the synthesis and transport of proteins

35
Q

Function and structure of ribosomes

A

ribosomes are the site of protein synthesis!!!
can be free-floating in the cytoplasm, or attached to endoplasmic reticulum forming RER.
Not surrounded by a membrane, and they are constructed of RNA molecules made in the nucleolus of the cell.

36
Q

Function and structure of Golgi apparatus

A

compacted structure of cisternae and does not contain ribosomes.
it has a role in modifying proteins and ‘packaging’ them into vesicles.

37
Q

Describe how a cell makes and secrets a protein

A
  1. The nucleus is the site of ribosome and mRNA manufacture
  2. Protein synthesis occurs on the ribosomes bound to the Rough endoplasmic reticulum (RER)
  3. Proteins are transported from RER to Golgi body by transport vesicles.
  4. Golgi body further processes the proteins (by adding sugar chains etc.)
  5. Vesicles containing proteins are ‘pinched off’ the go lei body, packaged into secretory vesicles and move towards the plasma membrane.
  6. Vesicles fuse with the plasma membrane and undergo exocytosis.
38
Q

Define Prokaryotic

A

single-celled organelles within a simple structure (uni-cellular) of just a single undivided internal area called the cytoplasm.

39
Q

Define Eukaryotic

A

make up multicellular organisms

more complicated internal structure as it contains a membrane-bound nucleus and cytoplasm