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OCR Biology A level > Foundations in Biology > Flashcards

Foundations in Biology Flashcards

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1
Q

2.1
How do you use a light microscope?

A

1) set up microscope
- place slide on stage using clips
-turn on light or adjust mirror
2) focus the specimen
- turn to lowest magnification (x40)
- turn coarse focus knob to raise stage to objective lens
- look through the eyepiece
3) turn up the magnification

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2
Q

2.2
What is the magnification equation?

A

Image size = Magnification x Actual size

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3
Q

2.1
What are the 4 ways to prepare a slide?

A

1) Dry mount
2) Wet mount
3) Squash slide
4) Smear slides

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4
Q

2.1
How does Dry mount work?

A

sectioning specimens; cut into thin slices with sharp blade. Place on centre of slide, place cover slip on top of sample
- used for hair, pollen, dust, muscle tissue, etc.

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5
Q

2.1
How does Wet mount work?

A

Specimen is suspended in liquid, e.g. water, or an immersion in oil. A cover slip is placed on from an angle
- used for things like aquatic samples

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6
Q

2.1
How does Squash slides work?

A

wet mount is prepared, a lens tissue is used to gently press down the cover slip - avoid potential damage by squashing the sample between 2 microscope slides.
- squash slides are a good technique for soft samples

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7
Q

2.1
How does Smear slides work?

A

edge of slide is used to smear the sample, creating a thin, even coating on another side. A cover slip is placed over the sample
- e.g. a blood sample

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8
Q

2.1
When was the cell first observed?

A

1665 by Robert Hooke
- He observed the structure of thinly sliced cork using early light microscope
- described compartments seen as ‘honeycomb’ like and named these boxes ‘cells’

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9
Q

2.1
How does staining help in microscopes?

A
  • Resolution is limited by wavelength of light and the diffraction of light as it passes through a sample
  • As most cell structures are usually transparent, images have low contrast as they don’t absorb light
  • Stains increase contrast as different components take up the stain to varying degrees, enabling components to become visible
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10
Q

2.1
Give 4 examples of stains

A

Iodine: stain commonly used to observe plant cells

Methylene blue: positively charged dye, attracted to negatively charged materials in cytoplasm

Congo red: negatively charged dye, repels negativity charged cytosol, stains outside of cell not inside

  • Eosin: negatively charged, acidic dye that binds to basic cell components
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11
Q

2.1
What are the 2 staining techniques?

A

1) Gram stain technique
2) Acid-fast technique

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12
Q

2.1
What is the Gram stain technique?

A

Used to separate bacteria into 2 groups: gram-positive and gram- negative
- crystal violet is first added to bacterial specimen -> slide is washed with alcohol -> gram-positive bacteria retain dye but gram-negative have thinner walls + lose stain
- gram-negative bacteria are stained with counter safranin, which makes them appear red

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13
Q

2.2
What is the definition of magnification?

A

How many times bigger the image size is than the actual object

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14
Q

2.2
What is the definition of resolution?

A

The ability to see individual objects as separate, the higher the resolution the clearer the image and more detail shown

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15
Q

2.3
What is diffraction?

A

The spreading of light, causes blurring and limits resolving power —> diffracting electron beams with shorter wavelengths get closer to each other without overlapping, reducing blurring and increasing resolution

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16
Q

2.3
What is an eyepiece graticule?

A
  • Glass disc with fine scale of 1 to 100
  • has no units
  • placed in eye piece
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17
Q

2.3
What is a stage micrometer?

A
  • placed on stage (then removed for sample)
  • 1mm long, each division is 1μm
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18
Q

2.2
What are the steps to calibrate a microscope?

A

1) Place stage micrometer under the clips on microscope stage
2) Turn the lowest power objective lens in nosepiece
3) align scales in eyepiece graticule and stage micrometer so that they’re parallel and there are 2 points of intersection

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19
Q

2.3
What is the definition of contrast?

A

The difference in shade or colour

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20
Q

2.3
What are the 4 microscopes?

A

Light microscopes:
- light microscope
- laser scanning confocal microscopy

Electron microscopes:
- Transmission electron microscope
- Scanning electron microscope

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21
Q

2.3
How does a light microscope work?

A
  • use light beams. Light passes through specimen + is refracted by 2 lenses which magnify imagine into our eyes
  • have lowest magnification of max. x1500
  • resolution max. Is 0.2 µm
  • used to look at whole cells or tissue (living or dead)
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22
Q

2.3
How does a Laser scanning confocal microscope work?

A
  • laser beam scans specimen tagged with fluorescent dye, causing dye to fluoresce
  • light is focused through pinhole onto detector, hooked up to computer
  • pinhole blocks out-of-focus light, producing 2D image with increased resolution
  • only focal plane will be in focus (you can view 1 layer of thick specimen at a time or stack layers to form 3D image)
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23
Q

2.3
How does a Transmission electron microscope work?

A
  • electromagnets used to focus beam of electrons, which are transmitted through specimen
  • denser parts absorb more electrons and appear darker
  • maximum magnification= x1,000,000
  • maximum resolution= 0.0002 µm
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24
Q

2.3
How does a Scanning electron microscope work?

A
  • electrons ‘scanned’ across specimen, which knocks off electrons from specimen. These are gathered in a cathode ray tube to form image
  • images show the surface of specimen and can be 3D
  • maximum magnification = x500,000
  • maximum resolution = 0.002 µm
  • image usually appears grey but colour can be added through editing
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25
Q

2.3
Where do both SEM and TEM microscopes need to be done?

A

Needs to be done in a vacuum

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26
Q

2.3
What are the maximum resolutions for the 4 microscopes?

A
  • Light - 0.02 µm
  • Laser scanning confocal - little higher than 0.02 µm
  • TEM - 0.0002 µm
  • SEM - 0.002 µm

The lower the resolution, the clearer + detailed the image

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27
Q

2.3
What are the maximum magnifications for all 4 microscopes?

A

Light - x1500
Laser scanning confocal - x1,000
TEM - x1,000,000
SEM - x500,000

The higher the magnification the better

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28
Q

2.4
What is a Eukaryote?
- how do they store DNA
- what do they contain
- give examples

A
  • An organism consisting of one or more cells that hold their DNA within a nucleus
  • They contain many specialised, membrane-bound organelles
  • Eukaryotes include: animals, plants, fungi, protists
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29
Q

2.4
What is the function of the Nucleus?

A

contains DNA, carries instructions for the cell - metabolism, enzymes

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30
Q

2.4
What is the function of the Nucleolus?

A
  • Site where ribosomes are assembled
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31
Q

2.4
What is the function of the Ribosome?

A
  • Either attached to RER or free in the cytoplasm
  • decodes the instructions contained in the mRNA to assemble protein
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32
Q

2.4
What is the function of the Endoplasmic reticulum (ER)?

A
  • Protein synthesis on RER (rough endoplasmic reticulum) and transports newly made protein through cell
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33
Q

2.4
What is the function of the Golgi apparatus/ body?

A
  • Process (structurally modifies) and packages protein
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34
Q

2.4
What is the function of the Vesicles?

A
  • Transports material from ER to Golgi apparatus to cell surface membrane or other sites in the cell, e.g. lysome
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35
Q

2.4
What are the steps in the protein production process?
(5 steps )

A

-The info in gene is copied into molecule mRNA. mRNA leaves nucleus and attaches to a ribosome, possibly attached to RER
1) Ribosome reads instructions + uses code to assemble hormone (protein)
2) Assembled protein inside the RER is pinched off into transport vesicle
3) Vesicles containing protein move via the cytoskeleton
4) Vesicles fuse with cis face of Golgi body + proteins enter. They’re structurally modified + packaged, ready for release
5) Secretory vesicles carry proteins to cell-surface membrane, where they fuse + release heir contents. Some vesicles fuse with lysosomes

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36
Q

2.5
Describe the features of a plant cell
- comparison with animal cells
- where is their energy from
- what are each cell surrounded by

A
  • Plant cells share all common features of animal cells, but also contain additional organelles
  • Plants gain all their energy from sunlight; cells in heir leaves contain many chloroplasts to convert the sunlight into useful form
  • Every plant cell is surrounded by a cell wall, and contains one or more permanent vacuoles
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37
Q

2.5
What is the function of a chloroplast?

A

photosynthesis - so they have to absorb as much sunlight as they can to make glucose

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38
Q

2.5
What is the structure of a chloroplast?

A

The network of internal membranes have a large surface area to contain more enzymes and chlorophyll pigments to enable an increased rate of photosynthesis

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39
Q

2.5
What are the (5) subcellular organelles in chloroplast?

A
  • Stroma
  • Double membrane
  • Lamella
  • Thylakoid
  • Granum
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40
Q

2.5
What is a Stroma?

A

Has appropriate enzymes and a suitable pH for the Calvin cycle

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41
Q

2.5
What is a double membrane evidence for?

A

Evidence for endosymbiosis

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42
Q

2.5
What is a Lamella?

A

Connects and separates thylakoid stacks (called grana)

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43
Q

2.5
What is a Thylakoid?

A

Has ETC and ATP synthesis for photophosphorylation

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44
Q

2.5
What is a Granum?

A
  • Flat membrane stacks increase surface area: volume ratio
  • Small internal volumes quickly accumulate ions
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45
Q

2.6
What is the Endosymbiotic theory?

A
  • An endosymbiont is a cell which lives inside another cell with mutual benefit
  • Eukaryotic cells are believed to have evolved from aerobic prokaryotes that were engulfed by endocytosis
  • Mitochondria and chloroplasts are suggested to have originated by endosymbiosis
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46
Q

2.6
What evidence is there that supports endosymbiosis?

A
  • Mitochondria and chloroplasts have their own DNA (which is naked and circular)
  • Mitochondria and chloroplasts have ribosomes that are similar to prokaryotes
  • Mitochondria and chloroplasts have a double membrane and the inner membrane has proteins similar to prokaryotes
  • Mitochondria and chloroplasts are roughly the same size as bacteria and are susceptible to the antibiotic chloramphenicol
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47
Q

2.6
What is the structure of the cell wall?

A
  • Made of the polysaccharide cellulose
  • Has pores called plasmodesmata
    (allow flow between cells. open network or cellulose allows flow of substances between cells)
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48
Q

2.6
What are the functions of the cell wall?

A
  • Strengthens the cell
  • Supports whole
  • Defence against pathogens
  • Permeable, allowing substances to flow from one cell to another in between cells
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49
Q

2.5
What do vacuoles consist of?

A

A vacuole consists of a membrane called the tonoplast, filled with cell sap - a watery solution of different substances, i.e. sugars, enzymes, pigments

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50
Q

2.5
What are vacuoles important for?

A

Important for keeping cell firm. When the vacuole is full of sap, the cell is said to be turgid

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51
Q

3.1
What are the key biological molecules?
- what do they contain

A
  • Carbohydrates: carbon, hydrogen, oxygen (usually in ratio Cx(H2O)x
  • Lipids: carbon, hydrogen, oxygen
  • Proteins: carbon, hydrogen, oxygen, nitrogen, sulfur
  • Nucleic acids: carbon, hydrogen, oxygen, nitrogen. phosphorus
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52
Q

3.1
Carbohydrates

A

polymer: glycogen
monomer: glucose
elements present: C, H, O
examples in organisms: cellulose (cell wall), starch/glycogen

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53
Q

3.1
Lipid

A

polymer: fast/ oils
monomer: fatty acids + glycerol
elements present: C, H, O
examples in organisms: cell membranes, steroid hormones

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54
Q

3.1
Protein

A

polymer: proteins
monomer: amino acids
elements present: C, H, O, N, S
examples in organisms: enzymes, hormones

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55
Q

3.1
Water

A

polymer: not a polymer
monomer:
elements present: H, O
examples in organisms: blood plasma

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56
Q

3.1
What is a monomer?

A

Single repeating units that are bonded together to form a polymer (has to be more than 2)

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57
Q

3.1
What is a dimer?

A

Two monomers joined together

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58
Q

3.1
How are polymers formed?

A

The monomers must undergo a condensation reaction, which will remove water (H2O)

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59
Q

3.1
How can a polymer be broken down?

A

This can occur through a hydrolysis reaction (the addition of water H2O), forming a monomer

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60
Q

3.1
What are the (5) cations and their uses?

A
  • Calcium ion (Ca2+) : nerve impulse transmission, muscle contraction
  • Sodium ions (Na+) : nerve impulse transmission, kidney function
  • Potassium ions (K+) : nerve impulse transmission, stomatal opening
  • Hydrogen ions (H+) : catalysis of reactions, pH determination
  • Ammonium ions (NH4+) : production of nitrate ions by bacteria
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61
Q

3.1
What are the (5) anions and their uses?

A
  • Nitrate ions (NO3,-) : nitrogen supply to plants for amino acid + protein formation
  • Hydrogen carbonate ions (HCO3,-) : maintenance of blood pH
  • Chloride ions (Cl-) : balance positive charge of sodium + potassium ions in cells
  • Phosphate ions (PO4,3-) : cell membrane formation, nucleic acid + APT formation, bone formation
  • Hydroxide ions (OH-) : catalysis of reactions, pH determination
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62
Q

3.2
What is cohesion?

A
  • the tendency of water to stick together
  • hydrogen bonds between water molecules
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63
Q

3.2
What is adhesion?

A
  • hydrogen bonds between water molecules and cell wall
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64
Q

3.2
What is surface tension?

A

where water meets air, tendency for water to be pulled back into the body of water

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65
Q

3.2
Does water have a high SHC and SLH of evaporation?

A
  • water has a high specific heat capacity (takes a lot of energy to raise 1cm3 of water by 1ºC), so less water evaporates
  • Has a high specific latent heat of vaporisation as a result of H-bonds in water (takes a lot of energy to evaporate 1gram of water), plants become less dehydrated
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66
Q

3.2
Why is water known as polar?

A

this is because oxygen, which is really electronegative is bonded twice with an atom with low electronegativity, H. this makes the electrons go closer to O, making it more negative, therefore H positive

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67
Q

3.2
How does water having a high specific heat capacity help animals?

A
  • Organisms in aquatic environments don’t experience large fluctuations in temperature
  • Terrestrial organisms are prohibited against sudden internal temperature changes
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68
Q

3.2
What does hydrophilic and hydrophobic mean?

A
  • Hydrophilic = water hating, repels water
  • Hydrophobic = water loving, capable of interacting with water, through hydrogen bonding
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69
Q

3.3
What are the 3 disaccharides and what 2 monosaccharides make them?

A

glucose + glucose = lactose
glucose + fructose = sucrose
glucose + galactose = lactose

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70
Q

3.3
What are the 2 types of glucose? What’s different about them
What is glucose? is it soluble in water?

A
  • Alpha glucose and Beta glucose have the same hexagon shape but the hydroxyl groups on carbon 1 is in opposite positions
  • Glucose (C6H12O6) has 6 carbon atoms
  • Glucose is water soluble due to hydrogen groups being polar and can hydrogen bond with water
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71
Q

3.3
What is an isomer?

A

They are molecules with the same molecular formula but different structures

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72
Q

3.3
What is ribose?

A

Ribose is in the pentose group as it has 5 carbon atoms and is also in the hydroxide group (made of hydrogen + oxygen)
- however, deoxyribose is just made of hydrogen

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73
Q

3.3
What occurs in every basic chemical reaction?

A

bonds are broken before bonds are formed, the atoms become rearranged

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74
Q

3.3
What are 6 polysaccharides?

A
  • Glucose
  • Amylose
  • Amylopectin
  • Starch
  • Glycogen
  • Cellulose
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75
Q

3.3
What is the structure and function of glucose?

A

STRUCTURE
- hexose monosaccharide with ring structure
- two isomers, α-glucose and β-glucose
FUNCTION
-

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76
Q

3.3
What is the structure and function of amylose?

A

STRUCTURE
- a helical, unbranched polysaccharide made of a-glucose molecules
- glycosidic bond linking a-glucose molecules is an a-1,4 glycosidic bond
FUNCTION
- stores energy

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77
Q

3.3
What is the structure and function of amylopectin?

A

STRUCTURE
- a branched polysaccharide
- bonds linking the a-glucose molecules are a-1,4 and a-1,6 glycosidic bonds
FUNCTION
- stores energy

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78
Q

3.3
What is the structure and function of starch?

A

STRUCTURE
- spiral molecule composed of amylose and amylopectin
FUNCTION
- water-insoluble molecule that stores energy in plant cells without affecting water potential

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79
Q

3.3
What is the structure and function of glycogen?

A

STRUCTURE
- highly branched polysaccharide
- the glycosidic bonds are readily hydrolysed, releasing the a-glucose molecules
FUNCTION
- energy store in animals
- stores excess glucose in muscle and liver cells
- the branching structure allows rapid hydrolysis to release glucose

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80
Q

3.3
What is the structure and function of celluluose?

A

STRUCTURE
- long (unbranched) polysaccharide chains made of b-glucose
Chains held by hydrogen bonds
FUNCTION
- provides structural support in plants
- prevents lysis during osmosis

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81
Q

3.4
What is the chemical test for proteins and what are the results?

A

• TEST: biuret test is added to the sample in solution. Leave for 5 mins and observe colour change

• RESULTS: positive test is purple
- usually uses a control of distilled water and sample with egg albumen

82
Q

3.4
What is the chemical test for reducing sugars and what are the results?

A

•TEST: Benedict’s reagent is heated to 80 degrees Celsius with a solution of the sample
- Reagent strips can be used for semi-quantitative results

• RESULTS: one heating, if reducing sugar is present, there’ll be a red or orange precipitate
- use colorimetry and calibration curve to quantify reducing sugars in sample

83
Q

3.4
What is the chemical test for non-reducing sugars (e.g. sucrose) and what are the results?

A

•TEST: if reducing sugar is not present, heat with HCl to reduce non-reducing sugar
- sodium hydrogen carbonate solution is added to neutralise the acid. Then Benedict’s reagent is added before heating to 80*C

• RESULTS: on heating is a non-reducing sugar is present, there will be a red or orange precipitate

84
Q

3.4
What is the chemical test for starch and what are the results?

A

•TEST: iodine solution is fuelled in to a sample (solid or liquid)

• RESULTS: positive test turns solution from yellow to blue/black

85
Q

3.4
What is the chemical test for lipids and what are the results?

A

•TEST: known as the emulsion test, the sample is dissolved first in ethanol and then water is added, then sample is shaken

• RESULTS: if lipids are present, the solution goes milky white

86
Q

3.5
What is the difference between saturated and unsaturated?

A

The R-group of a fatty acid may be saturated or unsaturated
- unsaturated lipids have one or more double bonds (C=C)

87
Q

3.5
What are lipids?

A
  • They are non-polar molecules containing carbon, hydrogen and oxygen - generally solid at room temp.
  • lipids are macromolecules (made of repeating units)
88
Q

3.5
What are triglycerides?
- properties
- what are they made of + how

A
  • they are not water soluble. Saturated molecules are usually solid at room temp.
  • they are synthesised by formation of 3 ester bonds between 1 glycerol molecule and 3 fatty acids - this is called esterification
89
Q

3.5
What are phospholipids?
- structure
- what do they form

A
  • phospholipids have a hydrophilic head and 2 hydrophobic tails
  • form phospholipid bilayer membranes
90
Q

3.5
What are the properties and functions of lipids? (Triglycerides)

A
  • they have a long hydrocarbon tail that stores energy
  • breakdown products can be used as a respiratory substrate
  • they can be stored in cells without affecting the water potential
91
Q

3.5
How are the hydrophibic properties of lipids used?
- Give examples

A

The hydrophobic properties of lipids are utilised in waterproofing in biological organisms
- such as the cuticles of leaves, exoskeletons of some insects, and bird feathers

92
Q

3.5
What are the properties and functions of lipids? (Cholesterol)
- what is it used to make

A
  • cholesterol is a lipid that functions as a steroid, is an essential component of prokaryotic + eukaryotic plasma membranes
  • it is used to make steroid hormones, vitamin D and bile
93
Q

3.5
What is the general structure of an amino acid?

A

R. NH2 = amine group
| COOH = carboxyl gr
H2N - C - COOH. R = side chain
|
H
The twenty amino acids that are common to all organisms differ from each other in side chain (R group)

94
Q

3.6
Synthesis of peptides - what are amino acids and how do they join together?

A
  • amino acids are the monomers of proteins
  • they can join together via a condensation reaction, forming peptide bond, with water as by-product
95
Q

3.6
Synthesis of peptides - how are are peptides and polypeptides formed?

A
  • a dipeptide molecule is formed by the condensation of 2 amino acids
  • a polypeptide is formed by condensation of many amino acids
96
Q

3.6
Synthesis of peptides - what are functional proteins, what do they contain?

A
  • a functional protein can contain one or more polypeptide (e.g. 1 molecule of haemoglobin contains 4 polypeptide chains)
97
Q

3.6
What are the 4 levels of protein structure?

A

1) primary
2) secondary
3) tertiary
4) quaternary

98
Q

3.6
Describe the primary structure and the function

A
  • the number and sequence of amino acids in the polypeptide chain
  • encoded by DNA and the mRNA
    • determines the structure of the polypeptide, and the 3D shape of proteins and their active sites
99
Q

3.6
Describe the secondary structure and the function - give examples

A
  • hydrogen bonds form between some amino acids to their pleat or twist a polypeptide
  • a single hydrogen bond is weak but many bonds give these structures stability
    • beta-pleated sheets are structural, like silk
    • alpha helixes make up DNA-binding and transmembrane proteins
100
Q

3.6
Describe the tertiary structure and the function - give examples

A
  • the final 3D specific shape of the polypeptide is held in place by ionic bonds, disulfide bonds, and H-bonds between R groups
  • it is also determined by hydrophobic and hydrophilic interactions
    • globular proteins (e.g. enzymes) or fibrous proteins (e.g. collagen)
101
Q

3.6
Describe the quaternary structure and the function - give examples

A
  • separate twisted or folded polypeptide linked together
  • non-protein, or prosthetic, groups may be associated with proteins having a quaternary structure
    • haemoglobin is made of 4 polypeptide chains, each with a prosthetic group haem (iron)
102
Q

3.7
What are the 2 different types of proteins?

A
  • globular proteins
  • fibrous proteins
103
Q

3.7
what are globular proteins?

A
  • spherical shape
  • water soluble because they have R groups on the inside that are hydrophobic, and ones on the outside the at are hydrophilic
  • involved in metabolic processes
104
Q

3.7
give + explain 3 examples of globular proteins

A

• haemoglobin; protein carries oxygen. Is known as a conjugated protein, made of 4 polypeptide chains + 4 haem prosthetic groups containing an iron (Fe2+) ion
• insulin; protein involved in controlling blood glucose levels. Made of 2 polypeptide chains (joined by disulfide bonds). It’s specific to shape of cell membrane receptors
• pepsin; an enzyme that functions in acidic environment of the stomach. Has few basic R groups, H-bonds, a disulfide bond

105
Q

3.7
what are fibrous proteins?

A
  • usually made of long polypeptide chains that form fibres
  • insoluble because they have amino acids with hydrophobic R groups
  • very strong, yet flexible
106
Q

3.7
give + explain 3 examples of fibrous proteins

A

• collagen; found in bones + tendons, allowing them to withstand large pulling forces. It’s also found in artery walls to allow them to cope with high pressures
• keratin; strong molecule that has a large amount of cysteine amino acids + therefore many disulfide bonds. It’s found in hooves, horns + fingernails
• elastin; an elastic fibrous protein found in walls of blood vessels, lungs + the bladder

107
Q

3.8
What is the structure of a nucleotide?

A
  • aucleotide is the monomer from which nucleus acids are made
  • each nucleotide is formed from a pentose sugar, nitrogenous organic base, and a phosphate group
  • both DNA and RNA are polymers of nucleotides
108
Q

3.8
What is DNA (deoxyribonucleic acid)?

A

It is a nucleotide that holds genetic information. The components are:
• deoxyribose sugar
• a phosphate group
• one of the organic bases:
- the purines; adenine (A) and guanine (G)
- the pyrimidines; cytosine (C) and thymine (T)

109
Q

3.8
describe the structure of DNA

A

DNA is a double-stranded molecule with a ladder-like structure, that twists into a double helix
- the 2 sugar-phosphate backbones are held in place by pairs of complementary bases joined by hydrogen bonds
- the 2 DNA strands are anti-parallel, running in opposite directions

110
Q

3.8
What is RNA (ribonucleic acid)?

A

The components are:
• a ribose sugar
• a phosphate group
• one of the organic bases:
- adenine
- cytosine
- guanine
- uracil (replaces thymine)

111
Q

3.8
What do condensation and hydrolysis reactions do in DNA and RNA?

A

• a condensation reaction between 2 nucleotides forms a phosphodiester bond to form a polynucleotide
• a hydrolysis reaction breaks the phosphodiester bonds between 2 nucleotides

112
Q

3.9
What occurs in DNA semi-conservative replication?

A

The semi-conservative replication of DNA ensures genetic community between generations of cells

1) DNA helipads breaks H-bonds between complementary base pairs
2) double helix unwinds + separates 2 DNA strands
3) New DNA nucleotides bind to exposed bases on DNA template strand
4) DNA polymerase catalyses the condensation reaction that joins adjacent nucleotides

113
Q

3.9
What is the genetic code?

A

The genetic code is carried as a sequence of 3 DBA bases, called a triplet or a codon
- most triplets code for a specific amino acid, but some code for STOP during transcription
- A gene is a sequence of triplets, specifying the order of amino acids of a polypeptide or protein

114
Q

3.9
What are the properties of the genetic code?

A

The genetic code is:
• Universal
• Non-overlapping
• Degenerate (most amino acids are coded for by more than one triplet code)

115
Q

3.10
What happens during protein synthesis?

A
  • a DNA template is transcribed into a mRNA molecule in the nucleus
  • the mRNA is then translated into an amino acid sequence in association with tRNA on ribosomes in the cytoplasm
116
Q

3.10
What occurs in transcription?

A

It is the production of mRNA from DNA
1) DNA helicase breaks H-bonds between bases, causing DNA to unzip + expose about 12 bases at a time
2) enzyme RNA polymerase moves along DNA template strand + attaches free nucleotides to bases on DNA
3) RNA polymerase continues making a strand of mRBA until it comes to a STOP codon

117
Q

3.10
What occurs in translation?

A

It is the production of polypeptides from the sequence of codons carried by mRNA
1) rNA makes up the ribosome that moves along mRNA strand
2) mRNA moves from nucleus via nuclear pore to cytoplasm + one AUG attaches to a ribosome
3) a tRNA with complementary anticodon (UAC), car egg ing specific amino acid (methionine), moves to ribosome + pairs with first mRNA codon
4) ribosome moves along mRBA to next codon + again pairs with complementary tRNA, to bring the 2 amino acid-carrying tRNAs together
5) energy released from ATP is used to form peptide bond between amino acids
6) ribosome moves to 3rd mRBA codon, releasing 1st tRNA + pairing up a 3rd
7) when ribosome reaches stop codon, polypeptide is complete + mRNA and tRNAs are released from ribosome
8) the tRNA molecules released from ribosome can be reused

118
Q

3.11
What is ATP?
- what is it made of
- What is its function

A

Adenosine triphosphate is a nucleotide and is formed from a molecule of ribose, a molecule of adenine, and three phosphate groups
- used for energy transfer in all cells in all living things - known as a universal energy currency

119
Q

3.11
What are the 3 main activities cells require energy for?

A
  • Synthesis: e.g. for a large molecule such as proteins
  • Transport: e.g. pumping molecules or ions across cell membranes by active transport
  • Movement: e.g. protein fibres in muscle cells that cause contraction
120
Q

3.11
What are the 5 properties of ATP?

A
  • small: moves easily into, out of and within cells
  • water soluble: energy-requiring process happen in aqueous environments
  • contains bonds between phosphates with intermediate energy: large enough to be useful for cellular reactions but not so large that energy is wasted as heat
  • releases energy in small quantities: quantities are suitable to most cellular needs, so that energy isn’t wasted as heat
  • easily regenerated: can be recharged with energy
121
Q

3.11
How does ATP release energy?
- what are the products

A

ATP undergoes a hydrolysis reaction which creates adenosine diphosphate, a single inorganic phosphate and energy

122
Q

5.1
Describe the structure of a membrane

A

Membranes are made up of a phospholipid bilayer. The fatty acids form a hydrophobic layer sandwiched between the hydrophilic phosphate heads - various proteins are associated with the bilayer
- carbohydrates are found attached to some lipids (gylcolipids) + some proteins (glycoproteins). Cholesterol is found between the fatty acids

123
Q

5.1
What is the arrangement of phospholipids and proteins known as?

A

It is known as the fluid-mosaic model:
- Fluid: the phospholipids move relative to each other
- Mosaic: the proteins, dotted between phospholipid , are of various shapes + sizes, like a mosaic

124
Q

5.1
What are the 2 types of proteins in the cell-surface membrane?
- What are their functions

A

• Intrinsic proteins
- span the bilayer
- are enzymes, carrier proteins + channel proteins
• Extrinsic proteins
- found in cell surface or embedded in one layer of membrane
- provide mechanical support
- in conjugated glycolipids, act as cell receptors for hormones + other molecules

125
Q

5.1
What are the other 4 components of a membrane?

A

• phospholipids
• glycoproteins
• glycolipids
• cholesterol

126
Q

5.1
What is the function of phospholipids?

A
  • down basic structure of a bilayer membrane, which is a partially permeable barrier
  • make membrane flexible
  • prevent the passage of water-soluble molecules
  • allow passage of lipid-soluble molecules
127
Q

5.1
What is the function of glycoproteins?

A
  • are receptors for chemical signals e.g. peptide hormones + neurotransmitters
  • act as receptors for toxins and drugs
  • role in cell adhesion in some tissues
128
Q

5.1
What are the functions of glycolipids?

A
  • have a role in cell recognition, acting as cell markers or antigens
129
Q

5.1
What is the function of cholesterol?

A
  • may be present; restricts movement of other membrane components, making membranes less fluid, proving mechanical stability
130
Q

5.3
What are the 6 types of membrane transport?

A
  • simple diffusion
  • facilitated diffusion
  • osmosis
  • active transport
  • endocytosis
  • exocytosis
131
Q

5.3
Explain simple diffusion

A
  • it’s the net movement of particles of a liquid or gas from an area of high conc. to an area of lower conc.
  • it’s a passive random process that uses kinetic energy of molecules
  • rate of diffusion can be affected by factors e.g. surface area, temperature
  • examples: lipid-based hormones, CO2, oxygen
132
Q

5.3
Explain facilitated diffusion

A

large, water-soluble molecules + charged ions can’t pass through phospholipid bilayer by simple diffusion. They move by facilitated diffusion which requires:
- channel proteins; these form ores in the membrane- often specific to an ion or a molecule
- carrier proteins; these change shape once an ion or a molecule attached to allow through the molecule

133
Q

5.4
Explain active transport

A
  • it’s the movement of substances across a membrane against the concentration gradient, using energy from hydrolysis of ATP
  • requires carrier proteins, called pumps which:
    • act as one-way carriers for specific molecules + ions across a membrane
    • require energy from hydrolysis of ATP to ADP and inorganic phosphate
    • carry molecules + ions against concentration gradient
    • transport molecules + ions much faster than diffusion
134
Q

5.4
Explain endocytosis

A
  • transports large quantities of material into, or out of, the cell
  • requires ATP as a source of energy
  • cell surface membrane wraps itself around material + brings it into cell into a vesicle. There are 2 main forms:
    • phagocytosis; for solid material
    • pinocytosis; for liquid material
135
Q

5.4
Explain exocytosis

A
  • transports large quantities of material into, or out of, the cell
  • requires ATP as a source of energy
  • the reverse of endocytosis, where a vesicle containing enzymes, mucus or hormones fuses with cell surface membrane to release materials out of the cells
136
Q

5.5
Explain osmosis

A
  • it’s the net movement of water particles by diffusion from a region of higher water potential to an area of lower water potential across a partially permeable membrane
  • water potential is a measure of ability of water molecules to diffuse; pure water has highest water potential of 0 kPa
137
Q

5.2
Explain the factors that affect membrane structure & permeability

A

Many factors increase permeability of phospholipid bilayer
- e.g. an increase in temp in trades permeability of, and therefore the rate of transport across, a membrane
- phospholipids have more kinetic energy, increasing relative movement + making membrane ‘leaky’
- if temp reaches long at which membrane proteins start to denature, a further increase in membrane permeability will occur
- organic solvents, e.g. ethanol, dissolve phospholipids + so will degrade the membrane, eventually destroying it, allowing substances to cross the membrane freely

138
Q

6.1
What are the two main phases in the eukaryotic cell cycle?

A

The two main phases are interphase and mitotic (division) phase

139
Q

6.1
What is interphase?

A

As cells don’t divide continuously, interphase occurs (long periods of growth + normal working separate divisions)
- sometimes referred to as the resting phase as cells are not actively dividing; although interphase is a very active phase, e.g. produces enzymes or hormones, while also preparing for cell division

140
Q

6.1
What occurs in interphase?

A
  • DNA is replicators + checked for errors in nucleus
  • protein synthesis occurs in the cytoplasm
  • mitochondria grow + divide, increasing in num. in cytoplasm
  • chloroplasts grow + divide in plant + algal cell cytoplasm increasing in num.
  • normal metabolic processes of cells occur, e.g. cell respiration through cytoplasm
141
Q

6.1
What are the different stages in interphase?

A

G1 - proteins required for organelles are synthesised
S - DNA replication takes place, resulting in a doubling of mass of DNA in the cell (2n —> 4n)
G2 - organelles grow + divide, + energy reserves are increased

142
Q

6.1
What are the other parts of the cell cycle?

A

• mitosis : the nucleus divides into 2
• cytokinesis : cytoplasm divides to form 2, genetically identical daughter cells

143
Q

6.1
Where are the checkpoints in the cell cycle?

A
  • the end of G1 before DNA replication is triggered
  • the end of G2 before mitosis begins
  • spindle assembly (or metaphase), to ensure chromosomes are aligned on spindle
144
Q

6.1
What is checked at each checkpoint?

A
  • G1: cell size, nutrients, growth factors, DNA damage
  • G2: cell size, DNA replication, DNA damage
  • Spindle assembly: chromosomes attached to spindle
145
Q

6.2
What are the 4 stages of mitosis? And what type of microscope is used to view them?

A

1) prophase
2) metaphase
3) anaphase
4) telophase
To view the stages of mitosis, a light microscope is used

146
Q

6.2
what is viewed in the prophase stage?

A
  • chromosomes comprise 2 genetically identical threads called sister chromatids, joined by centromere
  • chromosomes shorten + thicken by supercoiling + become visible under a microscope when stained
  • nuclear envelope disappears
  • centrioles live to poles of the cell, producing a network of spindle fibres between them
147
Q

6.2
what is viewed in the metaphase stage?

A
  • the chromosomes move to equation of the cell
  • the avg one becomes attached to a spindle fibre by its centimetre
148
Q

6.2
what is viewed in the anaphase stage?

A
  • the spindle fibres contract, which separates the sister chromatids
  • spindle fibres pull chromatids towards opposite poles of cell centromere first (v-shaped); each chromatid’s essentially a chromosome
149
Q

6.2
what is viewed in the telophase stage?

A
  • as the 2 sets of chromosomes reach each of the cell poles, a nuclear envelope forms around each one to form 2 new nuclei
  • chromosomes start forming uncoil
  • spindle fibres break down + disappear
  • after telophase, plasma membrane starts forming invaginate to divide the parent cell into 2 daughter cells (cytokinesis)
150
Q

6.2
Why is the life cycles of mitosis significant?
What do they used for?

A
  • asexual reproduction
  • growth
  • tissue repair
151
Q

6.3
What are the 4 stages of meiosis?

A

1) Prophase
2) Metaphase
3) Anaphase
4) Telophase

152
Q

6.3
What occurs in Prophase 1 in meiosis?

A
  • Chromatids condense
  • homologous chromosomes form bivalents
  • crossing over occurs
153
Q

6.3
What occurs in Metaphase 1 in meiosis?

A
  • bivalents line up at the equator
  • independent assortment occurs (random arrangement of maternal and paternal chromosomes)
154
Q

6.3
What occurs in anaphase 1 in meiosis?

A
  • spindle fibres pull homologous chromosomes to opposite poles of the cell
155
Q

6.3
What occurs in telophase 1 in meiosis?

A

In telophase 1 followed by cytokinesis, the nuclear envelope forms around new nuclei

156
Q

6.3
What occurs in prophase 2 in meiosis?

A
  • chromosomes condense
  • spindle re-forms
  • nuclear envelope breaks down again
157
Q

6.3
What occurs in metaphase 2 in meiosis?

A
  • chromosomes randomly arrange themselves on spindle fibres at equator by centromeres
  • so independent assortment occurs
158
Q

6.3
What occurs in anaphase 2 in meiosis?

A
  • chromatids are pulled apart by contracting spindle fibres to poles of the cell
159
Q

6.3
What occurs in telophase 2 in meiosis?

A
  • In telophase 2 followed by cytokinesis, the nuclear envelope forms around new haploid nuclei
160
Q

6.3
What is the significance of meiosis in the cell cycle ?
What is the end results? Exaplain

A

Results in 4 in identical daughter cells, called gametes. Each daughter cell is:
- haploid; half the chromosome number of diploid parent cell (23 instead of 46)
- genetically unique; have unique set of alleles due to independent assortment + crossing over

161
Q

6.3
What are homologous chromosomes?

A

They are a pair of chromosomes that have the same genes at the same loci (location)

162
Q

6.3
Explain what crossing over is, when does it occur in the cell cycle?

A

During prophase 1, homologous chromosomes form bivalents so that non-sister chromatids (i.e. maternal + paternal chromatids) can cross over at locations called chiasmata + exchange sections of chromosome holding the same genes but potentially different alleles

163
Q

6.3
What is independent assortment, when does it occur?

A

This is caused by the random distribution + separation of homologous chromosomes during metaphase 1 and the random distribution + segregation of sister chromatids at metaphase 2

164
Q

4.1
What are enzymes?

A
  • They are biological catalysts - they speed up rate of reaction but remain unchanged and can be used again
  • they catalyse a wide range of intracellular (e.g. catalase) and extracellular reactions (e.g. amylase + trypsin)
165
Q

4.1
What is the structure of an enzyme?

A

They are specific to a particular substrate. Only the active site of an enzyme is functional. The active site has a tertiary structure, which is complementary to the substrate

166
Q

4.1
What occurs when an enzyme binds to a substrate?

A
  • when an enzyme binds to its substrate, an enzyme-substrate complex is formed. The reaction takes place, making an enzyme-products complex
  • After the reaction, the products leave the active site and the enzyme is free to bind with more substrate
167
Q

4.1
What is the function of an enzyme?

A

Each enzyme catalyses the reaction by lowering its activation energy (minimum energy required to start a chemical reaction), but the rate of reaction is at its highest when it takes in the optimal conditions for the enzyme

168
Q

4.1
How does the lock and key theory work?

A
  • shape of active site on enzyme is complementary to substrate molecule
  • substrate fits into active site exactly on collision
  • an enzyme-substrate complex is formed
  • the reaction occurs
169
Q

4.1
How does the induced-fit theory work?

A
  • shape of active site on enzyme isn’t fully complementary to substrate molecule
  • when substrate molecule collides with active site, enzyme molecule changes shape
  • an enzyme-substrate complex is formed
  • the reaction occurs
170
Q

4.1
What are 3 additional molecules or ions some reactions require?

A
  • co-enzyme
  • cofactor
  • prosthetic group
171
Q

4.1
What is a co-enzyme?
- give an example

A

it is an organic molecule that, when present, increases the activity of an enzyme
- e.g. nicotinamide adenine dinucleotide (NAD) assist electron transport enzymes

172
Q

4.1
What is a cofactor?
- give an example

A

it is an inorganic ion
- e.g. chloride ions assist amylase reactions

173
Q

4.1
What is a prosthetic group?
- give an example

A

it is a tightly bound non-amino acid component necessary for enzyme activity
- e.g. zn2+ on carbonic anhydrase

174
Q

4.2
how do you investigate the effects of variables on enzyme activity?

A
  • when a reaction produces a gas, the volume of gas per unit time can be measured to estimate the rate of reaction under different conditions, e.g. temp., pH or enzyme or substrate concentrations
  • some products can be identified sing an indicator or chemical test. these reactions can be set up + samples of reaction can be tested at time intervals
175
Q

4.2
What are inactive precursors?

A

They are non-working enzymes that are synthesised to prevent cell damage
- a precursor molecule inhibits proteases to stop them damaging the cell. Only when proteases are needed is the precursor removed by chemical reactions + proteases become active

176
Q

4.2
How does enzyme concentration effect enzyme activity?

A
  • higher enzyme concentration increases number of active sites
  • more enzyme-substrate complexes form. The reaction rate increases until substrate concentration becomes the limiting factor
177
Q

4.2
How does substrate concentration effect enzyme activity?

A
  • higher substrate concentration increases number of enzyme-substrate complexes formed, so rate of reaction increases
  • when all enzyme active sites are working, enzyme concentration will become limiting factor
178
Q

4.2
How does temperature effect enzyme activity?

A
  • enzymes have diff. optimum temps. (temp which enzymes work at max rate)
  • raising temp. increases rate of reaction following temperature coefficient (Q10)
  • Temp coefficient (Q10) for specific reaction is the effect of a 10ºC rise in temp. on the rate of reaction
  • above enzyme temp. rate of reaction slows. if enzyme becomes denatured, reaction stops
179
Q

4.2
What is the equation to work out Q10?

A

Q10= rate of reaction at (T+10)ºC
rate of reaction at TºC

180
Q

4.2
How does pH effect enzyme activity?

A
  • diff. enzymes have diff. optimum pHs (the temps. which enzymes can work at optimum rate)
  • above and below optimum pH, rate of reaction decreases
  • pH affects hydrogen and ionic bonds holding the active site in its 3D shape
181
Q

4.3
What are inhibitors?
- what are the 2 types
- what could be the possible outcomes once bonded with an enzyme

A

Enzyme inhibitors control metabolic reaction. This allows product to be made in very specific amounts. There are 2 types:
- competitive inhibitors
- non-competitive inhibitors
Binding between these types and the enzyme can be: irreversible + permanent or reversible + non-permanent

182
Q

4.3
What is a competitive inhibitor?

A
  • compete for enzyme active site with substrate
  • an active site blocked by competitive inhibitor isn’t able to catalyse a reaction - rate of reaction slows
183
Q

4.3
What is a non-competitive inhibitor?

A
  • bind to non-functional part of enzyme (allosteric site) + change specific shape of active site
  • substrate can’t fit into active site, enzyme-substrate complexes don’t form, + rate of reaction decreases
184
Q

4.3
How do enzymes work in metabolic pathways?

A
  • metabolic pathways, e.g. photosynthesis + respiration are made of a chain reaction, each controlled by enzymes
  • enzyme inhibitors play role in controlling these reactions
  • e.g. final product of pathway acts as an inhibitor of an enzyme earlier in that pathway, creating a negative feedback loop
185
Q

4.3
How do inhibitors act as metabolic poisons?
- give an example

A
  • some enzymes involved in metabolic processes can be inhibited by poisons, leading to illnesses or even fatality
  • e.g. carbon monoxide is a competitive inhibitor with oxygen for haemoglobin, which is what makes it potentially fatal
186
Q

4.3
How are enzyme inhibitors utilised in medicine

A

Enzyme inhibitors can be used in medicine to treat diseases. E.g.:
- methotrexate is used in chemotherapy to inhibit enzyme dihydrofolate reductase, blocking DNA replication
- penicillin is an enzyme inhibitor that interferes with cell wall production, causes bacterial cells to burst

187
Q

6.4
What is an Erythrocyte and how is it specialised to carry out its function?

A

It is a red blood cell which contains haemoglobin to transport oxygen from lungs to body tissues

188
Q

6.4
What is a Neutrophil and how is it specialised to carry out its function?

A

It is a type of white blood cell involved in phagocytosis, with a cytoplasm filled with lysosomes to break down phagocytosed material

189
Q

6.4
What is a Squamous Epithelial cell and how is it specialised to carry out its function?

A

Found lining surfaces such as the lungs, blood vessels, + the oesophagus. Has a flat, thin shape to facilitate diffusion of materials across it

190
Q

6.4
What is a Ciliated Epithelial cell and how is it specialised to carry out its function?

A

Has tiny extensions called cilia to move mucus along mucous membranes e.g. in respiratory tract) or ova along the fallopian tubes

191
Q

6.4
What is a Sperm cell and how is it specialised to carry out its function?

A

Flagellum used to swim to ovum using energy released by hydrolysis of ATP in mitochondria in middle section

192
Q

6.4
What is a Root Hair cell and how is it specialised to carry out its function?

A

Long ‘hair’ maximises surface area in contact with soil for uptake of water + mineral ions

193
Q

6.4
What is a Palisade cell and how is it specialised to carry out its function?

A

Long + thin so that the many chloroplasts can absorb maximum sunlight

194
Q

6.4
What is a Guard cell and how is it specialised to carry out its function?

A

Arranged in pairs around stomata to control water vapour loss from plant. Guard cells have a thickened cell wall surrounding the pore which causes the bending of the cell when it is turgid

195
Q

6.5
What are stem cells?
- what are the 3 different types

A

They are cells that have not differentiated yet into specialised cells. stem cells can divide an unlimited number of times, + are a renewing source of undifferentiated cells
- 3 types: totipotent, pluripotent, multipotent

196
Q

6.5
What are totipotent cells?

A
  • occur only for a limited time in early mammalian embryos
  • can differentiate to produce any type of blood cell, including placental cells
197
Q

6.5
What are pluripotent cells?

A
  • found in embryos
  • can differentiate into all tissue types, except placental cells
198
Q

6.5
What are multipotent cells?

A
  • found in many tissues at any post-embryonic life stage
  • can differentiate o form a limited number of different cell types
199
Q

6.5
How are the xylem and phloem of a plant differentiated?

A
  • xylem vessels + phloem sieve tubes differentiate from plant meristems
  • plant meristems are totipotent + can differentiate into many different cells
200
Q

6.5
How do meristem cells differentiate to form xylem and phloem cells?

A
  • meristem cells that are destined to become xylem vessels elongate. Lignin is deposited into the cell walls to strengthen + waterproof them, + the cell dies. End cell walls break down to form long, continuous tubes
  • meristem cells forming phloem differentiate into companion cells + sieve tube elements
201
Q

6.5
What are the potential uses of stem cells in research and medicine?

A
  • Stem cells are potential treatments for some human neurological disorders, e.g. Parkinson’s + Alzheimer’s
  • Also have potential to be used to repair damaged tissue, e.g. breaks in spinal cords causing paralysis, or injured heart muscle after heart attack
  • Also being used for research into developmental biology to help scientists understand how a fertilised egg cell develops into a multicellular organism, + how and why the process can go wrong

OCR Biology A level (5 decks)

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