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unit 1/ Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Define osmosis

A

Net movement of particles from a higher region of water potential to a lower region of water potential through a partially permeable membrane

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2
Q

Define homeostasis

A

Organisms that need to maintain their internal environment

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3
Q

Name 3 negative feedback effects

A
  • pH
  • temperature
  • water potential
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4
Q

Define negative feedback effect

A

Body’s mechanism for reversing change and retuning it back to optimum conditions

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5
Q

What are the steps for negative feedback including effectors , receptors and coordinators

A

1 - receptors detect change in optimum conditions and send signals to coordinators
2 - the coordinators decides which receptors are appropriate by sending signals to effectors
3 - the effectors change internal conditions back to optimum conditions

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6
Q

Where are temperature receptors located

A

Skin
Hypothalamus

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7
Q

What is the positive feedback effect?

A

Opposite of negative feedback effect
Any changes away from optimum conditions are increased

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8
Q

Name an example of positive feedback and explain

A
  • action potential
  • the influx of sodium ions causes depolarisation which results to more sodium channels to open
  • therefore membrane potential increases
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9
Q

Where does transcription take place in?

A

The nucleus

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10
Q

Where does mRNA move to?

A

The cytoplasm

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11
Q

What are the steps for transcription?

A

1 - DNA helicase breaks hydrogen bonds between the 2 strands
2 - complimentary RNA nucleotides move into place and form hydrogen bonds with bases on the exposed nucleotides on one of the DNA strands
3 - enzyme RNA polymerase joins RNA nucleotides by forming phosodiester bonds
4 - once mRNA has been synthesised the RNA polymerase detaches from the DNA and the DNA goes back into its normal double helix structure
5 - mRNA moves out of the nucleus from nucleus pores
6 - once in cytoplasm, mRNA can take part in translation

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12
Q

What are the steps for translation

A

1 - once the mRNA moves from the nucleus to the cytoplasm a small subunit of ribosome binds with the mRNA at the start codon
2 - the tRNA molecules with an anticodon complementary to the start codon attaches and is held by hydrogen bonds between the complementary base pairs on mRNA and tRNA
3 - a 2nd tRNA molecule moves into place
4 - peptide bonds are formed between the 2 amino acids
5 - ribosome moves to the next codon and the first tRNA molecules has ben released
6 - when ribosome reaches to the stop codon the polypeptide chain is released

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13
Q

Where is mRNA created in?

A

Nucleus

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14
Q

Why does mRNA leave the nucleus?

A

To carry the Copy of the genetic code of one gene to a ribosome in the cytoplasm

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15
Q

Why is mRNA much shorter than DNA?

A

It is only the length of 1 gene and therefore can leave the nucleus

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16
Q

Where is tRNA found in?

A

Cytoplasm

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17
Q

What is the structure of tRNA

A

Single stranded
Cloverleafed shape that is held by hydrogen bonds

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18
Q

What does rRNA make up?

A

Bulk of ribosomes by combining with proteins

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19
Q

How are nucleotides formed?

A

By phosphodiester bonds

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20
Q

What 5 molecules are the fluid mosaic model

A
  1. Phosphobilayer
  2. Glycoprotein
  3. Glycolipids
  4. Proteins
  5. Cholesterol
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21
Q

What are the differences between the phosphobilayer head and tails

A
  1. Tail is hydrophilic as it has no charge
  2. Head is hydrophobic as it is negatively charged
  3. Head contains glycerol and phosphate group
  4. Tails contain fatty acid chains
22
Q

What does cholesterol do in the membrane?

A

Restrict movement of the molecules

23
Q

What are 2 types of protiens?

A

Peripheral
Integral

24
Q

What are peripheral proteins?

A

Proteins that do not extend completely across the membrane and are there for mechanical support and to connect lipids or proteins into glycoproteins and glycolipids

25
Q

What are integral protiens?

A

Proteins that extent fully to the membrane and are used for protein carriers / channels for transport of molecules across the membrane

26
Q

What protein structure are enzymes?

A

Tertiary

27
Q

What is induced fit?

A

When the active site slightly changes shape to mould around the substrate

28
Q

What happens to the bonds in induced fit?

A

Weakens and activation energy is lowered

29
Q

What are the 5 factors effecting enzyme action?

A
  • pH
  • temperature
  • inhibitors
  • enzyme concentration
  • substrate concentration
30
Q

How does pH affect enzyme activity?

A

If pH is too low or too high it can interfere with the charges in the amino acids in the active site.
This can break bonds in the tertiary structure so active site changes

31
Q

How does enzyme concentration effect enzyme activity?

A

If there is insufficient enzyme - the enzymes active site will be more saturated with the substrate and will be unable to work faster

32
Q

How does substrate concentration affect enzyme activity?

A

If there is insufficient substrate the reaction will be slower and fewer collisions happen between enzymes and substrate

33
Q

What is and describe a competitive inhibitor?

A

Has the same shape as substrate and binds to the active site temporarily so it prevents the substrate from binding, this lowers rate of reaction
By adding more substrate this will out compete the inhibitor

34
Q

Describe non competitive inhibitors

A

Binds away from the active site
Causes active site to change shape so substrate is no longer complimentary to the active site

35
Q

What are 3 samples of monosaccharides?

A

Glucose
Galactose
Fructose

36
Q

What is a property of monosaccharides?

A

Soluble in water

37
Q

What are OH groups called?

A

Hydroxyl groups

38
Q

What are isomers?

A

Same formula but different arrangement of atoms

39
Q

What does non polar means?

A

Not easily dissolved in water - hydrophobic

40
Q

What does substrate mean?

A

Surface where organisms live on

41
Q

What is active site?

A

Enzyme where Substrate binds to undergo a chemical reaction

42
Q

Why do we need ATP? 2 reasons

A

For energy
Hydrolysis of one of the 3 phosphate groups of the ATP to provide energy

43
Q

What are the roles of ATP?

A
  • metabolic processes - build large complex molecules from a smaller molecule
  • active transport - changes shape of carrier proteins in membrane and allows molecules and ions to move against a concentration gradient
  • muscle contraction / movement
44
Q

Why is there a leading strand and a lagging stand in DNA replication?

A

Leading strand - replicate continuously
Lagging strand - replicate forming short fragments discontinuously

45
Q

What is a gene?

A

Segment of DNA that codes for a protein

46
Q

Name 3 examples of a disaccharide

A
  • maltose
  • sucrose
  • fructose
47
Q

What are 4 properties of polysaccharides?

A
  • large
  • compact
  • insoluble
  • easily broken down
48
Q

What are triglycerides made of?

A

3 fatty acids + glycerol

49
Q

Explain the test for proteins

A

Biuret solution - turns from blue to purple if present

50
Q

Explain the test for lipids

A

Ethanol and water - cloudy / white if present

51
Q

How does the body regulate water potential?

A
  • If the water potential is lower than set point it is detected by Osmoreceptors
  • This causes ADH to be released from the pituitary gland - ADH is the coordinator in the feedback loop
  • ADH travels from blood into the kidneys nephron
  • The cell linings in the collecting duct and distal convoluted tubule have ADH receptors on them
  • ADH causes vesicles of aquaporins to fuss with the membrane increasing permeability of the collecting duct to water
  • Water moves out by osmosis to the medulla and into the blood, concentrating the urine and reducing water loss
52
Q

What does ADH stand for?

A

Antidiuretic hormone

medical science (2 decks)

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