Cell Biology

Question 1

Organelle

Answer 1

Small structure within a cell that carries out specific cellular functions (typically membrane bound in Eukaryotes with own lipid bilayer membrane)

Question 2

Summary Nucleus

Answer 2

Contain and protect DNA; transcription;

Partial assembly of ribosome in nucleolus

2 surrounding Membranes

Question 3

Summary Mitochondria

Answer 3

Produce ATP via Krebs cycle and oxidative phosphorylation

2 surrounding membranes

Question 4

Summary Ribosomes

Answer 4

Synthesize proteins

Not membrane bound

Question 5

Summary Rough Endoplasmic Reticulum

Answer 5

Location of synthesis/modification of secretory, membrane-bound, and organelle proteins

1 surrounding membrane

Question 6

Summary Smooth Endoplasmic Reticulum

Answer 6

Detoxification and glycogen breakdown in liver, steroid synthesis in gonads

1 surrounding membrane

Question 7

Summary Golgi Apparatus

Answer 7

Modification (i.e. Glycosylation) and sorting of protein, some synthesis

1 surrounding membrane

Question 8

Summary Lysosomes

Answer 8

Contain acid hydrolases that digest various substances

1 surrounding membrane

Question 9

Summary Peroxisomes

Answer 9

Metabolize lipids and toxins, releasing H2O2

1 surrounding Membrane

Question 10

Nucleus

Answer 10

Site of replication, transcription, splicing

Contains the genome and surrounded by nuclear envelope. Not a fluid membrane, nuclear matrix/scaffold supports the organelle and provides overall structure

Question 11

Genome

Answer 11

Eukaryotic Genome organized into linear molecules of double stranded DNA (Chromosomes)

Genes can be mapped genetically and physically to the chromosome they reside on (a locus)

Nuclear matrix may play a role in regulating gene expression (DNA in chromosomes attached to matrix at specific sites)

Question 12

Nucleolus

Answer 12

Region within nucleus that functions as the ribosome factory

Consists of loops of DNA, RNA polymerases, rRNA and protein components of the ribosome (to partially assemble the ribosome)

Ribosome maintained inactive until exported from nucleus and assembled fully in cytoplasm

Question 13

Nuclear Envelope

Answer 13

2 lipid bilayer membranes. Inner facing inside, outer facing cytoplasm.

Outer membrane continuous with some membrane of the ER (lumen)

Envelope is punctuated with nuclear pores that allow things to enter and exit the nucleus (smaller than 60 kD) –> larger proteins must contain a nuclear localization sequence that imports them into nucleus (after cytoplasmic ribosome translation)

Question 14

Chromatin

Answer 14

Heterochromatin - densely packed chromatin with inaccessible genes (turned off)

Euchromatin - loosely packed chromatin that allows genes to be activated

Question 15

Mitochondria

Answer 15

Site of Oxidative Phosphorylation

Matrix is interior of the mitochondria (bound by innter and outer membranes) that contains enzymes of the Krebs Cycle

Inner membrane of the mitochondria is location of ETC and ATP synthase (impermeable and folded into projections called cristae)

Space between two membranes is known as intermembrane space

Exhibit Maternal Inheritance

Question 16

Endosymbiotic Theory of Mitochondrial Evolution

Answer 16

Mitochondria originated as independent unicellular organisms living within larger cell

Question 17

Mitochondrial Genome

Answer 17

Smaller version of cellular genome consisting of single circular DNA molecule

Encodes for rRNA, tRNA, several proteins (including what’s necessary for ETC and ATP Synthase complex)

Question 18

Endoplasmic Reticulum

Answer 18

Rough ER - ribosomes bound to surface, site of protein synthesis for proteins targeted to enter secretory pathway

Smooth ER - Not actively involved in protein processing; can contain enzymes involved in steroid hormone biosynthesis or in degradation of environmental toxins

Question 19

Rough ER

Answer 19

Protein Synthesis occurs in either free ribosomes or RER-bound ribosomes

Post-translational modification of proteins occurs in Rough ER (ex. glycosylation, disulfide bond formation)

All Protein translation starts in cytoplasm. Signal sequence means translation is continued on in rough ER ribosomes

Question 20

Secretory pathway

Answer 20

If N-terminus has signal sequences, protein is a part of the secretory pathway/endomembrane system.

Recognized via signal recognition particles, the signal sequence is removed and translation continues in cytoplasm on free ribosomes.

No signal Sequence means translation continues in cytoplasm on free ribosomes

Question 21

Signal Sequence (+)

Answer 21

Default (nothing but signal sequences) results in secretion

Transmembrane domain (special signal sequence not removed) means the protein has hydrophobic residues, allowing it allow localization to the plasma membrane (integral membrane protein)

Otherwise, needs a targetting signal to go elsewhere (GEL = Golgi, E.R., Lysosome)

Question 22

Signal Sequence (-)

Answer 22

Default is cytoplasm

With a localization signal, can go to either nucleus, mitochondria, or peroxisome

Question 23

Golgi Apparatus

Answer 23

Modification of proteins made in RER (important in the modification of oligosaccharide chains)

Sorting an sending proteins ot their correct destination

Synthesizes macromolecules (ex. polysaccharides) for secretion

Protein traffic at Golgi apparatus is unidirectional (cis -> trans) but protein route is determined by signals within the protein that determine which vesicle a protein is sorted into in the trans

Question 24

Cis/trans stack of Golgi

Answer 24

Cis - portion nearest rough ER
- Vesicles from ER fuse with this stack where they are modified and transfered

Medial - middle
Then sent to medial stack

Trans - farthest from rough ER

• Pass Through Trans stack, protein leave golgi in transport vesicles
• As vesicle moves from trans Golgi to surface, fuses with cell membrane (contents released extracellularly via exocytosis unless proteins bound to vesicle membrane)

Question 25

Constitutive Secretory Pathways

Answer 25

Take protein from Golgi to cell surface immediately

Question 26

Secretory Vesicles

Answer 26

Specialized cells have a regulated secretory pathway that releases proteins only at certain times (B-cells, pancreatic cells)

Question 27

Lysosomes

Answer 27

Responsible for degradation of biological macromolecules by hydrolysis using acid hydrolases (hydrolyze only in acidic environments)