Topic 2: Cell structure + function

Question 1

Define plasma membrane

Answer 1

• Fluid lipid bilayer embedded with proteins + cholesterol

Question 2

Define phospholipid bilayer

Answer 2

• Polar hydrophilic head
• 2 nonpolar hydrophobic fatty acid chains
• Assemble in bilayer = separates from ICF/ECF
• Passage barrier = water soluble substances
• Fluid mosaic

Question 3

Give other molecules that are a part of membrane

Answer 3

• Cholestrol = stability
• Carbohydrates = glyco/proteins/lipids
• Proteins attached on/in = channels + carriers + receptors + bound enzymes

Question 4

Describe nucleus

Answer 4

• Surrounded by nuclear envelope + nuclear pores
• Contains genetic material = DNA

Question 5

Define DNA

Answer 5

• Carries genetic info = blueprint for cell replication
• Directs protein synthesis

Question 6

Give organelles found in cytoplasm

Answer 6

• Endoplasmic reticulum
• Golgi
• Lysosomes
• Peroxisomes
• Mitochondria
• Vaults

Question 7

Describe role of cytosol

Answer 7

• Enzymatic regulation of intermediary metabolism
• Protein synthesis in ribosomes
• Storage = fat + carbs
• Cytoskeleton

Question 8

Describe ER

Answer 8

• Protein + lipid synthesis
• Fluid-filled membrane
  1) RER: ribosomes attached + flattened sacs
• Proteins synthesized to lumen
• Lipids synthesized for cell wall
  2) SER: interconnected tubules
• Packaging for molecules to be released
• Transport vesicle bud off → golgi for further processing
• Detoxify endo/exogenous substances
• Calcium storage

Question 9

Explain protein synthesis in the ER

Answer 9

• Ribosomes start protein synthesis → segment + binds to signal-recognition protein in cytoplasm = pauses synthesis
• SRP + ribosome → RER
• SRP + transmembrane receptor on RER = docking
• Docking = resume synthesis
• Synthesis + translocation to ER occur simultaneously

Question 10

Describe golgi

Answer 10

• Stack of flattened membrane-enclosed sacs = cisternae
• Post-translational modification

Question 11

Give the post-translational modifications of the Golgi

Answer 11

• Glycosylation
• Disulphide bonds
• Folding
• 4’ structure
• Sorting + directing

Question 12

Describe mRNA

Answer 12

• Long single nucleotide = half DNA
• Carry instructions for protein synthesis from DNA in nucleus → ribosomes in cytoplasm

Question 13

Describe tRNA

Answer 13

• Small = 70-80 nucleotides
• Clover leaf shape
• Transfer amino acid molecules to mRNA

Question 14

Describe transcription

Answer 14

• Complementary mRNA = made at DNA
• 3-base sequence on the DNA = specify a
  particular amino acid
• Corresponding 3-base sequences on
  mRNA = codons

Question 15

Describe lysosomes

Answer 15

• Intracellular digestive system
• Small sac = hydrolytic enzyme
• Different sizes
• Break down organic molecules from foreign materials
• Material internalized = via endocytosis

Question 15

Describe translation

Answer 15

• mRNA = decoded to assemble proteins in a
  ribosome using tRNA
• Language of base sequence = translated into language of proteins
• mRNA from the nucleus attaches → ribosome in cytoplasm
• tRNA transports an amino acid → mRNA strand + recognizes mRNA codon + amino acid by binding its anticodon to codon
• Ribosome moves mRNA strand along as each codon is read
• As each amino acid is bound to the next by a peptide bond = its tRNA is released
• Polypeptide chain is released when the termination codon is read

Question 16

Describe peroxisomes

Answer 16

• Detoxify waste products + foreign toxic compounds
• Similar structure to lysosome = smaller
• Contain oxidative enzymes = remove H from organic molecules = produces H2O2

Question 17

Give the 3 types of endocytosis

Answer 17

1) Pinocytosis
2) Receptor-mediated endocytosis
3)Phagocytosis

Question 18

Describe pinocytosis

Answer 18

• Bring ECF into cell
• Coat proteins bind to ECF side = membrane dips = dynamin pinches bud off

Question 19

Describe receptor-mediated endocytosis

Answer 19

• Selective process to internalize needed molecules
• Molecules + receptor = proteins coat ICF side = membranes sink in + seal at surface
• Needed for cholesterol + Vit B12 + insulin + iron uptake
• Used by viruses to enter cell

Question 20

Describe phagocytosis

Answer 20

• INternalization of latge multimolecular particles
• By phagocytes = come across foreign particle
• Extension of pseudopod = internalize into vesicle = fusion with lysosome = break down engulfed material
• Useful byproducts

Question 21

Describe mitichondria

Answer 21

• Generate 90% cells energy
• Amount varies on cell type + energy needed
• Size = like bacteria
• Have own DNA
• Mitochondrial DNA can be passed down from mother to child

Question 22

Give examples of mitochondrial inherited diseases

Answer 22

• Rare
  1) Mitochondrial encephalopathy + lactic acidosis + stroke episodes = MELAS
  2) Myoclonic epilepsy + ragged red fibers = MERRF
  3) Neuropathy + ataxia + retinitis pigmentosa = NARP

Question 23

Describe the structure of mitochindria

Answer 23

• Double membrane
• Smooth outer membrane
• Inner membrane = cristae
• Matrix = enzymes for citric acid cycle

Question 24

What is the function of cristae?

Answer 24

- Increase surface area - Contains enzymes = ETC

Question 25

Explain how energy is derived from C-C bonds

Answer 25

- Ingested food→ broken up to absorbable units - Carbs → glucose = absorbed into blood → delivered to tissues - Uptake of molecules into cells

Question 26

Explain how energy is processed to usable form

Answer 26

- High energy phosphate bonds of ATP = split→ P+ ADP + energy - For glucose to become usable = glycolysis + citric acid cycle + ETC

Question 27

Describe glycolysis

Answer 27

- Location: cytosol - 10 sequential reactions - Glucose → 2 pyruvic acid + 2 ATP - Not efficient = most energy still in pyruvic acid

Question 28

Describe citric acid

Answer 28

- Location = mitochondria - O2 required - Each pyruvic acid = 2 ATP - CO2 + H released - H binds to hydrogen carrier molecules for ETC

Question 29

Give the hydrogen carrier molecules

Answer 29

1) Nicotinamide adenine dinucleotide = NAD = from Vit B niacin 2) Flavine adenine dinucleotide = FAD = from Vit B riboflavin

Question 30

Describe the ETC

Answer 30

- Oxidative phosphorylation - e- carriers arranged in order within cristae - Carrier molecules = deliver hydrogen + high energy e- to chain - e- moves down chain via energy to move H in intermembrane space - After 3 transports e- = passed to O2 → H2O - Hydrogen returns back to matrix via ATP synthase channels

Question 31

Describe mitochondrial pH

Answer 31

- H+ ions taken up by Krebs + ETC = NADH + FADH + H2O - H+ conc low in matrix = pH high = 7.8

Question 32

How many ATP are made from 1 glucose molecule?

Answer 32

- Total 34 ATP - Glycolysis = 2 ATP - Citric acid cycle = 4 ATP - Oxidative phosphorylation = 28 ATP

Question 33

Describe anaerobic respiration

Answer 33

- Produce ATP in O2 absence 1) Glycolysis = make ATP 2) Lactate formation = regenerate NAD+

Question 34

When is anaerobic respiration used regularly?

Answer 34

- Skeletal muscle fiber = energy for short burst strenuous exercise - RBC = no mitochondria + not many metabolic needs

Question 35

Describe vaults

Answer 35

- New organelle - Ribonucleoprotein complex = contain untranslated RNA - Octagonal-shaped barrel structure - Function = transport molecules from nucleus to cytoplasm

Question 36

Describe the function of cytoskeleton

Answer 36

- Maintain structure + shape of cells - Movement of parts/whole cell - Signalling

Question 37

Give the 3 parts of the cytoskeleton

Answer 37

1) Microtubules - Tubulin forming tubes - 22nm diameter 2) Microfilaments - Actin + myosin forming twisted strands - 6nm diameter 3) Intermediate filaments - Various proteins forming irregular thread-like strand - 7-11 diameter

Question 38

Give functions of microtubules

Answer 38

1) Maintain asymmetric shapes: - Stabilize long axon of neurons 2) Facilitate complex movement

Question 39

Describe microtubules facilitate movement of secretory vesicles

Answer 39

- Transport vesicles from golgi - Transported along microtubule→ axon terminal = Kinesin - Debris transported back = Dynein - Mechanism also used by viruses

Question 40

Describe microtubules facilitate movement of cilia

Answer 40

- Numerous tiny hair-like protrusions - Beat in unison - E.g. respiratory tract move foreign bodies - E.g. oviducts move ovum to the uterus

Question 41

Describe microtubules facilitate movement of flagellum

Answer 41

- Single whip-like appendage - E.g. sperm movement + alignment with ovum

Question 42

Describe the structure of cilia/flagella

Answer 42

- 9 double around 2 single microtubules - Dynein arms - Sliding of tubes along each other = motion

Question 43

Describe the formation of mitotic spindle

Answer 43

- During mitosis DNA chromosomes = duplicated = need to be divided equally between 2 daughter cells - Pulled apart by mitotic spindle = transiently assembled microtubules starting from tubelike structures = centrioles

Question 44

Give the functions of microfilaments

Answer 44

1) Cell contracrile system: - Contraction of muscles - Contractile ring during cell division 2) Mechanical stiffener for cell projections

Question 45

Describe how microfilaments facilitate cell locomotion

Answer 45

- White blood cells/fibroblasts/amoeboid movement - Pseudopods extend + contract to move the cell - Actin networks which grow at the leading edge + simultaneously disassembled at rear

Question 46

When do microfilaments facilitate mechanical stiffeners?

Answer 46

- Microvilli = non motile projections of epithelial cells

Question 47

Give the functions of intermediate filaments

Answer 47

1) Maintain cell structural integrity 2) Resist external applied stress 3) Vary composition to suit cell type needs