Cell Structure + Function

Question 1

Nucleus

Answer 1

brain of the cell

2 layer membrane studded by nuclear pore complexes
- selective passage of proteins + RNAs in/out of cell

Contains:
- chromatin = heterochromatin (inactive) + euchromatin (active)
- nuclear proteins
- RNA
- nucleolus

Question 2

DNA Packing + Organization

Answer 2

DNA is negatively charged = attracted to positive charge
- histone proteins
- hematoxylin (blue) stain

basic structural unit of chromatin = nucleosome
- strand is wrapped around 8 histone proteins

modification of these histone proteins:
- loosen chromatin = allow access (transcription/replication)
- tighten chromatin = shut off access (transcription/replication)

Question 3

Transcription

Answer 3

Generation of RNA sequence by RNA polymerase II
- mRNA, rRNA, tRNA

gene = sequence of DNA read to develop a particular mRNA encoding a protein

regulaed in various ways:
- transcription factors
- enhancers
- repressors
- epigenetics

Question 4

Cell Cycle

Answer 4

overall goal = ensure appropriate DNA replication + integrity

regulation achieved by interplay of multiple proteins:
- cyclins
- cylcin-dependant kinases (CDKs)
- CDK-inhibitors
- p53
- Rb

checkpoints ensures DNA integrity before + after replication (S phase)

if all is well, cell is allowed to complete replication via mitosis (M phase)

Question 5

DNA Repair

Answer 5

mistakes can still be made during replication (not common)

constant bombardment by DNA damaging agents + ageing

mechanisms in place to replair DNA damage:
- many small alterations in DNA can be fixeed with high rate of fidelity = NER used most often
- larger alteratins more challenging to fix - repair not as consistent and may result in mutation

Question 5

Nucleolus

Answer 5

site at which rRNA transcribed + ribosomal subunits are assembled

rRNA utilized in diagnostics to determine bacterial + fungal identification (PCR + sequencing)
- bacteria = 16S - 23S
- fungi = 5S - 18S
- eukaryotes = 18S - 28S

larger nucleolus = mpre protein synthesis

Question 6

Ribosomes

Answer 6

synethesize proteins from mRNA (translation)
- free within cytosol = proteins destined to stay in cytosolm nucleus, mitochondria
- attached to ribosome = proteins destined for secretion, membrane, ER, Golgi, lysosomes

mRNA encodes AA sequence that forms proteins
- each 3 mRNA bases = codon
- codon = amino acid (20 AA) + stop codons + start codons

translational regulation
- repressors
- modification of initiation factors

Question 7

Rough Endoplasmic Reticulum

Answer 7

processes + sorts proteins destined for secretion, plasma membrane, ER, golgi or lysosomes
- this further processing required for proteins to become functional

Modifications:
- folding into correct 3D conformations via chaperone proteins
- assembly of polypeptides into multi-subunit proteins
- disulfide bond formation
- initial stages of glycosylation
- addition of glycolipid anchors for membrane proteins

Question 8

Smooth Endoplasmic Reticulum

Answer 8

lipid metabolism + membrane lipid synthesis
- mol. processes through rER -> bound in vesicles -> membranes or Golgi

major production site of molecules composed of lipids
- i.e. steroid hormones derived from chol.
- adrenal cortical cells often foam

major role in metabolizing lipid-soluble compounds
- home of cytochrome p450s in hepatocytes
- inactivates numerous drugs by converting them to water-soluble compounds -> eliminated by urine

Question 9

Acetominophen Toxicity

Answer 9

cats lack glucoronyl transferase to break down drug via glucoronidation

alternate routes of detoxifying processes also easily overwhelmed
- sulfation
- depletion of glutathione excess

increased amount of drug in bloodstream that is metabolized by p450 (in the sER of hepatocytes) -> production of toxic metabolite NADQPI -> hepatocellular necrosis

Question 10

Golgi Apparatus

Answer 10

post office

receives proteins from ER

processes + sorts them for transport to eventual destinations:
- lysosomes
- plasma membrane
- secretion

Question 11

Lysosomes

Answer 11

waste + recycling center

membrane-bound

contains array of enzymes

degrades material from endocytosis
- engulfed material from outside cell by pinching of plasma membrane -> vesicle
- vesicles merges with endosomes

degrades obsolete cell componenets (autophagy)

Question 12

Phagocytosis

Answer 12

Question 13

Mitochondria

Answer 13

power plant

generates ATP from breakdown of carbs + FAs

1) citric acid (kreb’s)
- ATP, NADH, FADH2, CO2

2) oxidative phosphorylation (electron transport chain)
- creation of PE storw that drives ATP synthase protein
- ATP

Question 14

Cytoskeleton

Answer 14

Question 15

Membrane Proteins

Plasma Membrane

Answer 15

Transport across membrane

Passive diffusion
- gases, hydrophobic mol. , small polar mol.
- conc, gradients

facilitated passive transport
- channel proteins = voltage-/ligand-gated
- carrier proteins

active transport = requires energy (often ATP)

endocytosis

cell-to-cell adhesion + barrier function
- tight junctions
- adherens junction
- desmosomes

anchoring to BM
- hemidesmosomes

cell-to-cell communication + nutrient transfer
- gap junctions

specialized cell-to-cell adhesion
- allows cells to adhere only to toher cells of specific types

four major groups of cell-adhesions mol. (CAMs)
- selectins
- integrins
- immunoglobulin superfamily (IgSF)
- cadherins

Question 16

Cell Signaling

Answer 16

cell-cell contact
- gap junctions
- juxtacrine (membrane-bound ligands)

secreted signaling mol.
- autocrine, paracrine, synaptic/neural, endocrine

signaling mol.
- gases to complex proteins
- when interacting wiht receptor on target cell = ligand

Question 17

Membrane Proteins

Cell Signaling

Answer 17

targets receptors for cell communication

ligand-gated ion channels

GPCRs (7 transmembrane receptors)
- largest family of receptors

enzyme-linked receptors
- tyrosine kinase
- tyrosine phosphatase
- seronine/threonine kinase

cytokine/chemokine receptors

pattern recognition receptors
- TLRs
- NLRs
- CLRs
- RLRs

cluster differentiation (CD) markers