Cell Structure & Intracellular Organelles: An Overview

Question 1

nucleus

Answer 1

largest organelle, most cells have 1, however, skeletal muscle have >1 and RBCs have 0.
Contains the cell’s DNA complexed with histone proteins to form chromatin.

Question 2

nucleosome

Answer 2

complex of 8 molecules of histones around which DNA is wound, appears as beads on a string. Fundamental subunit of chromatin.

Question 3

heterochromatin

Answer 3

highly condensed DNA-protein complex, DNA is inaccessible to transcription factors, and thus is “silent” in this configuration (DNA methylated and histones deacetylated)

Question 4

euchromatin

Answer 4

less condensed DNA-protein complex, DNA is accessible to transcription factors and thus is transcriptionally active. (DNA demethylated and histones acetylated)

Question 5

nucleolus

Answer 5

most prominent structure within nucleus, site of rRNA trancription, pre-rRNA processing and ribosome subunit assembly
***Cells that are active in protein synthesis such as liver cells and some highly proliferative cancer cells have increased numbers of these.

Question 6

nuclear pores

Answer 6

small, protein-lined openings in the nuclear envelope that allow for exportation of RNAs and ribosomes from nucleus to cytosol, as well as importation of transcription factors

Question 7

mitochondria

Answer 7

organelle that converts PE from food into cellular energy under aerobic conditions, have a highly porous outer membrane and an inner membrane that is impermeable to many ions, including protons, and is convoluted, forming folds called cristae. Site of e- transport chain

Question 8

mitochondrial diseases

Answer 8

genetic disease group that is passed down from mother to all children, variable disease symptoms/expression can occur in these diseases due to different mutation loads: can be different # mutations per organelle, different # organelles with mutations per cell, and different # cells with mutated organelles per tissue/organ system.

Question 9

ribosomes

Answer 9

protein synthesizing machinery of the cell, free scattered in the cytosol or bound to ER membrane. Made up of large and small subunits (Euks: 80S = 60S + 40S, Proks: 70S = 50S + 30S)

Question 10

80s, 60s, 40s

Answer 10

eukaryotic ribosomal subunits

Question 11

endoplasmic reticulum

Answer 11

network of flattened sacs and branching tubules that extends throughout the cytoplasm, function to produce and process various proteins, lipids, toxins

Question 12

rough ER

Answer 12

organelle covered in ribosomes, involved in production and processing of membrane-embedded and secretory proteins

Question 13

smooth ER

Answer 13

organelle involved in production of lipids, detox of drugs and poisons, and calcium storage

Question 14

golgi apparatus

Answer 14

organelle made up of several flattened, stacked sacs, referred to as cisternae. Considered the shipping and distribution center for the cell’s chemical products - modifies proteins and distributes things back to ER or out to cell membrane. Protein modifications here include: glycosylation, sulfation, phosphorylation, and proteolysis.

Question 15

cis

Answer 15

face of golgi apparatus where substances enter from the ER for processing

Question 16

trans

Answer 16

face of golgi apparatus where substances exit in vesicles or lysosomes

Question 17

lysosome

Answer 17

organelle that is filled with hydrolytic enzymes, degrades intracellular molecules - primarily degrades extracellular proteins that were taken up by endocytosis or engulfed by autophagosomes. Lumen is acidic which activates the enzymes (hydrolases).

Question 18

peroxisomes

Answer 18

small organelles that contain enzymes linked to metabolic pathways such as beta oxidation of long-chain fatty acids. The enzymes use molecular oxygen to neutralize free radicals, releasing H2O2, which must be converted to H2O by catalase. (most abundant in liver cells)

Question 19

proteasomes

Answer 19

small cytoplasmic protein complexes degrade proteins, involved in the quality control of endogenously synthesized proteins by marking misfolded and denatured proteins for degradation, also degrades TFs, cyclins, and proteins encoded by viruses and intracellular pathogens.
**Uses polyubiquitination to tag for degradation.

Question 20

centrosome

Answer 20

consists of a bound pair of centrioles surrounded by a shapeless matrix of dense material. During cell division - directs migration of chromosomes to opposite ends of the cell (spindle apparatus). In non-dividing cells, centrioles attach to the inner side of the membrane to form a basal body - which forms a cilia/flagella or non-motile primary cilium.

Question 21

membrane asymmetry

Answer 21

negatively charged lipids are usually found on the inner leaflet of the plasma membrane while positively charged lipids are found on the outer leaflet. Disorganization of this usually indicates cell damage.

Question 22

flippases

Answer 22

one of the 3 protein families responsible for the generation, maintenance, regulation, and dissipation of lipid asymmetry in the plasma membrane; this protein moves lipids from the outer monolayer to the inner monolayer with the help of ATP (because this is against the gradient)

Question 23

floppases

Answer 23

one of the 3 protein families responsible for the generation, maintenance, regulation, and dissipation of lipid asymmetry in the plasma membrane; this protein moves lipids from the inner monolayer to the outer monolayer with the help of ATP (because this is against the gradient)

Question 24

scramblases

Answer 24

one of the 3 protein families responsible for the generation, maintenance, regulation, and dissipation of lipid asymmetry in the plasma membrane; this protein exchanges lipids between monolayers in either direction toward equilibrium, without the use of ATP.

Question 25

facilitated diffusion

Answer 25

movement of solutes bidirectionally from areas of low concentration to areas of high concentration; does not require ATP - going with its gradient; rate of diffusion can hit a max (saturation) at which point increased concentration of solute will not increase rate. Ex: channel proteins, carrier/transporter proteins

Question 26

channel proteins

Answer 26

form a pore in the cell membrane, highly specific for a particular ion, facilitate diffusion leading to equilibrium; can be always open, voltage-gated, ligand-gated, mechanically-gated.
*Due to finite # of these, there is a saturation pt at which increased concentration of substrate will not increase the rate of diffusion.

Question 27

transporter/carrier proteins

Answer 27

facilitate diffusion of molecules bidirectionally across a membrane by binding its substrate, inducing a change in shape that moves the bound molecule through the lipid bilayer
*Due to finite # of these, there is a saturation pt at which increased concentration of substrate will not increase the rate of diffusion.

Question 28

active transport

Answer 28

transport that requires ATP and is concentrative - meaning that the solute can be moved against its concentration gradient.

Question 29

primary active transport

Answer 29

directly uses ATP to drive transport of solutes across a membrane; frequently called pumps, ex: NA+/K+ pump kicks out 3 Na ions and lets in 2 K ions per cycle.

Question 30

secondary active transport (cotransport)

Answer 30

indirectly uses ATP to drive transport; uses electrochemical gradients generated by active transporters such as the Na/K pump as an energy source to move molecules against their gradient. Further divided into symporters and antiporters.

Question 31

symporter

Answer 31

secondary active transporter that moves both substrates in the same direction

Question 32

antiporter

Answer 32

secondary active transporter that moves its substrates in opposite directions

Question 33

other cellular roles of electrochemical gradients

Answer 33

1. cell communication - ex: neurons use Na channel to allow influx of Na to enter cytosol, thus depolarizing neuron and allowing for signaling through the action potential
2. regulate enzyme activity - ex: many enzymes require Ca2+ to work, cells can essentially turn enzymes on and off by opening calcium channels and increasing or decreasing cellular calcium concentration
3. regulate cellular secretion - ex: insulin secreted by beta islet cells

Question 34

sodium potassium pump creates these 3 gradients

Answer 34

1. Outside to inside Na+ gradient
2. Inside to outside K+ gradient
3. Inside cell negative membrane potential