Lec 11 - Anatomy of cell nucleus and cytoplasm

Nuclear envelope structure/function

s: lipid bilayer

f: spatial separation b/w transcription and translation

Nucleolus structure/function (Nucleolar organizing region (NOR) - ribosomal RNA production)

s: densely wrapped RNA

f: site of rRNA transcription/processing/ribosomal assembly

2 types of chromatin

1. Euchromatin: loosely wrapped, transcriptionally active

2. Heterochromatin: tightly wrapped, transcriptionally inactive

Chromatin structure/function

s: DNA wrapped around histones to form nucleosomes

p: depending on type, used for transcription

Rough ER structure/function

s: membrane-bound ribosomes

f: ER captures select proteins from cytosol

Components of Nucleolus (3)

1. Dense Tubular Component

2. Granular Component

3. Fibrillar Center

Nucleolus - Dense Tubular Component

newly formed rRNA

Nucleolus - Granular Component

pre-ribosomal subunits site of assembly

Nucleolus - Fibrillar Center

rRNA genes, RNA polymerase, signal recognition particle (SRP)

Nuclear Pore structure/function

s: lets certain proteins in/out by either passive diffusion or energy dependent transport

f: entry/exit from nucleus to cytoplasm

Nucleoporins structure/function

s: proteins of nuclear pore complex (NPC)

f: anchors nuclear membrane to lamins

Nuclear Localization Signal (NLS)

string of amino acids that sends a signal

Steps for transport through NPC

1. protein w/ NLS interacts w/ specific nuclear import receptor (importin)

2. Moves through NPC outside to in

3. Ran-GTP required

4. Cargo released

Steps for transport out NPC

1. protein must have nuclear export sequence (NES). allows binding to exportin complex

2. GTP required to exit

3. Once exited, protein dissociates from exportin complex

hydrophilic signaling molecules ____ cross cell membranes

do not

hydrophilic signaling molecules interact with cell _____________

surface receptors (ex: neurotransmitters, ligands)

hydrophobic molecules (e.g. steroids) are typically _______ and then _____ across membrane

carried, diffused

Nuclear lamins during the cell cycle get _________ and ________ for nuclear envelope to re-from

phosphorylated, dephosphorylated

Cell Cycle Steps

G1 - grow

Synthesis - DNA replication

G2 - 2nd growth phase

Mitosis phase - cell division

Normal differentiated cells are _________ (G0) during cell cycle

quiescent

What controls the cell cycle?

cyclin dependent kinases (Cdk)

Cdk steps in the cell cycle

1. cDK is unbound (inactive)

2. cDK is bound with cyclin, partial activation, conformational change displaces T-loop

3. cDK is bound and phosphorylated T-loop, it’s at full activity

When are the 3 checkpoints for the cell cycle

1. after G1

2. G2 to M

3. after M

What is retinoblastoma (cancer) protein (Rb)

regulates cell cycle at the level of checkpoint 1 (after G1)

What is p53 gene

identifies whether DNA has been replicated appropriately and whether or not the cell can pass into mitosis

T/F? Phosphorylated Rb lets the cell continue to S phase

True

T/F? less of p53 mutations drive mitosis

true