SP16 BILD 1 Midterm 2Review Session

Cell Organization o Cell basics

o Microscopy

o Prokaryotes vs eukaryotes

o Cell Organization and Organelles

o Endosymbiosis

Cells are relatively small o This assures a high surface to volume ratio

o facilitates fast exchange of material with the extracellular environment

Microscopyo Two key aspects of microscopy:o Magnification

o Resolution

o Light microscopyo Fluorescence, phase-contrast, and confocal

o Electron microscopy o Scanning EM and transmission EM

Prokaryotes vs EukaryotesProkaryotes:

o DNA - free in the cytoplasmo Single circular “nucleoid”

o Have plasmids

o No membrane bound organelles

o Structural support (outside)o Cell wall – peptidoglycan

o Capsule - polysaccharide

Eukaryotes:

o DNA - enclosed in nucleuso (multiple) linear chromosomes

o No plasmid

o Have membrane bound organelles

oStructural support (both inside & outside)o Inside: cytoskeleton – protein

o Outside:

• Animal Cell - extracellular matrix (ECM) - protein

• Plant Cell - cell wall - cellulose/polysaccharide

Mitochondriao Energy processing organelle - Respiration

o Double membraneo Cristae: infoldings of the inner membranes

o More surface area to pack lots of ETC and ATP synthase

o Has its own DNA – circular (similar to prokaryotes)

o Has own ribosomes

Chloroplastso Plants only – Photosynthesis

o Double membrane

o Has own DNA – circular

o Has ribosomes

Endosymbiosis Theoryo Explained how organelles of eukaryotes originated as a symbiosis between separate single-celled organisms

o Mitochondria and Chloroplasts:o Double membrane enclosed

o Same size as bacteria

o Has own DNA that is circular

o Ribosomes are bacteria-like

o Respiration or photosynthesis – known prokaryotic activities

Nucleuso Stores DNA – the genetic information

o Is the site for transcription and ribosome biosynthesisothe nucleolus – site for rRNA synthesis

o Is enclosed by a double membrane – “nuclear envelope”o Nuclear pore complex - regulate traffic in and out

o linked with ER membrane

o Has its own internal skeleton - nuclear lamina

Ribosomeso Synthesize proteins

o Are not considered organelles o b/c they are not membrane-enclosed

o Both prokaryotes and eukaryotes have ribosomes

Two types of ribosomes:

o Bound ribosomes (on the surface of rough ER)o make membrane and secreted proteins

o Free ribosomes omake cytosolic proteins

Endoplasmic ReticulumRough ER:

o Linked to nuclear membrane

o Single membrane

o Where bound ribosomes reside

o Make all secreted and membrane proteins

o Makes all organellar proteins

o Involved in protein folding/modificationo Glycosylation – addition of sugars

Smooth ER:

o Single membrane

o Detoxification of Drugs

o Phospholipid synthesis

Golgi Apparatuso The sorting organelle – protein modification/transport

o Adds additional glycosylation (zip codes)

o All membrane/secreted proteins must pass through the Golgi

o Single membraneo cis face (receiving side)

o trans face (shipping side)

How does the cell transport transmembrane/secreted proteins from rough ER to plasma membrane? 2 fission and 2 fusion events

First fission First fusion

Second fission

Second fusion

Lysosomeo Digestive Organelle

o digest damaged organelles/proteins and food that enters the cell by phagocytosis

o Low pH – acidic environment

o Contain lots of proteases

Membrane structure and function

Lecture 9

Membrane

● Semipermeable● Fundamental unit: phospholipid● Cholesterol, carbohydrates, proteins● Fluid mosaic model

○ Proteins move about the membrane■ Inside phospholipid bilayer: non-polar R-groups

○ Adjusted by changing the degree of saturation○ Cholesterol

Fission and Fusion● Fission

○ 1→2○ Vesicles leaving ER or Golgi○ Cell division○ Endocytosis

● Fusion○ 2→1○ Vesicles from ER to Golgi○ Fertilization○ Virus infection○ Exocytosis

Endocytosis

● Phagocytosis○ Food contained in vesicle → lysosome (digested)

● Pinocytosis○ Soluble components → vacuole

● Receptor-mediated endocytosis○ Ligand → Receptor (transmembrane protein) →

Receptors cluster → Invagination → recruit clathrin → pinch off vesicle → clathrin falls off

Permeability

● Most permeable○ Small / non-polar molecules

■ CO2 , CH4, O2 ● Least permeable

○ Large / polar molecules■ Sugars, amino acid, proteins

Diffusion

● Molecules go from HIGH TO LOW concentration.● Rate is proportional to [solute]● Osmosis is the diffusion of water across a selectively

permeable membrane

Osmosis

● Isotonic○ No net flow

● Hypertonic○ Cell surrounded by HIGHER [solute] environment○ Water LEAVES the cell → SHRINK

● Hypotonic○ Cell surrounded by LOWER [solute] environment○ Water ENTERS the cell → BURST

Proteins reside at membranes

● Integral membrane proteins○ Penetrate the hydrophobic core○ Transmembrane protein

■ Span the entire lipid bilayer (~10-20 a.a. In length)● Peripheral proteins

○ Loosely bind to plasma membrane (Interact with integral membrane proteins)

○ Some partially embed in plasma membrane

~20a.a

Six major functions of Integral membrane proteins

1. Transport2. Enzymatic activity3. Signal transduction4. Cell recognition5. Intercellular joining6. Attachment of the cytoskeleton to the extracellular matrix

Transport

Enzymatic activity

Signal Transduction

Cell recognition

Intercellular joining

Cytoskeleton attached to ECM

Cytoskeleton

● Link the cell to extracellular matrix○ ECM made of glycoprotein○ Collogen, proteoglycans, fibronectin

● Link the cells together○ Tight junction

■ Link neighboring cells together so components can’t get through

Internal Cytoskeleton

● Microtubules (MT)○ Tubulin

● Microfilaments○ Actin

● Intermediate filament○ Keratin

Microtubule: organelle movement & motility

● Central assembly point for MT: Centrosome (MT organizer)

● Motor proteins move along MT○ Kinesin (away from nucleus)○ Dynein (towards nucleus)

● Motility - Dynein○ Flagella, cilia Video on the website!

Microfilaments: Cell shape & motility

● Changes in cell shape are related to motility● 3 types of cell shape

a. Microvilli■ Increase surface area

b. Lamellipodia■ Membrane ruffles

● Sense environment● Direct movement

c. Filopodia■ Increase surface area (less stable than microvilli)■ Sense environment (can turn into lamellipodia)

Microfilament: actin-based motility

Video on the website!

Transport: moving molecules across the membrane

1. Diffusion: depends on concentration gradienta. Simple diffusion

i. Small / non-polar molecules (CO2 , O2, etc)b. Facilitated diffusion

i. Small molecules (water)ii. Channel proteiniii. Carrier protein

Channel protein

Carrier protein

Transport: moving molecules across the membrane

2. Active transport

a. Primary active transporti. Uses ATP directlyii. Conformational change (phosphorylation)

b. Secondary active transporti. Energy provided by concentration gradient

(previously made using ATP)ii. Co-transporter

Restores resting membrane potential after depolarization of active potential

Action potential

● Depolarization○ Sodium rushes into the membrane

● Repolarization○ Potassium flushes out

Questions?

Lecture 10 Cell Signaling

What’s Required?

Signal-"er” Signal Signal Receiver

How does cell signaling happen?

Signal Reception

• Signals come in many varieties

• Need a receptor to detect them

• Receptors are SPECIFIC and have a SPECIALIZED function/response

• Variety of receptors are expressed virtually everywhere on the surface and inside the cell.

Transduction

• Main goal is to AMPLIFY the signal.How?-Phosphorylation cascade• Kinase (enzyme) adds phosphates

onto the Threonine, Serine, or Tyrosine residues of moleculesActivates more residues.

-Second Messenger• Receptor-ligand complex activates

enzymeMakes a new product that acts as a messenger (which can bind allosterically to target).

Phosphorylation

• One of the “main languages” cells use to turn things on/off

• The characteristics of a Phosphate group cause whatever it’s attached to to rearrange shape = altered state (can be on/off)

Ultimate Goals of Signaling

• Growth

• Apoptosis

• Danger (Infection/Inflammation)

• Turn genes ON/OFF

Local vs Long Distance Signaling

Local:

• Autocrine- Cell secretes a signal that affects itself

• Paracrine- Cell secretes a signal that affects its neighboring cells

Long Distance:

• Hormones: Can be peptides (proteins) or steroids (non-polar, bulky molecules). Use CV system

Receptor Types

Intracellular Receptors:• Specific for steroids (hormones)• Steroids are big, bulky,

hydrophobic molecules = can diffuse through the membrane

• Upon ligand binding, will usually move into the Nucleus to affect gene transcription

Receptor Types

Tyrosine Kinase:

• Transmembrane protein receptors that bind outer signal

• Binding leads to dimerization, which activates its kinase ability

• Phosphorylates itself and other proteins = ON

• PhosphoTASE cleaves off phosphates = OFF

Receptor Types

G-Protein Coupled Receptors (GPCRs):

• Has 7 transmembrane α-helices

• Ligand binds outer portion of receptor, allowing cytosolic G-protein interaction.

• Binding allows the G-protein to exchange its bound GDP (similar to ADP) for GTP (similar to ATP) = ON

• After a while, the GTP will be hydrolyzed to GDP = OFF

Receptor Types

Ion Channels:

• Usually a transmembrane pore or channel.

• Ligand binding will open channel to select ions = ON

• Sudden increase of ions (Na+) inside causes an ACTION POTENTIAL (depolarization) Signal

• Will close membrane channel= OFF

Second Messenger Signaling

Cyclic-AMP (cAMP):

• Produced by GPCR signaling

• A major component of GPCR-mediated signal amplification

• Signals proteins to turn ON or OFF

Second Messenger Signaling

Calcium Signaling (Ca2+):

• Triggered by action potentials

• Calcium is released from organelles/structures

• Turns other proteins ON/OFF

SUMMARY

• Cells have a variety of receptors that are specific towards unique signals that allow for diverse cell-cell communication. SPECIFIC.

• Not all cells express the same proteins, so a signal in one cell might have the opposite effect on a different type of cell. DIVERSE.

• Transduction serves to receive a small signal and AMPLIFY it to produce a fast, sufficient response.

• The methods by which cells signal each other is equivalent to us using different languages. Proper communication is key for growth.

Meiosis and the Sexual

Life Cycle

Lecture 12

Key Concepts

• Why is meiosis performed?

• Genetic Variation

• Heredity: transmission of traits from one generation to the next

• Sexual Life Cycle

• Creates gametes for fertilization

• Diploid (2n) vs Haploid (n)

• Difference between Mitosis and Meiosis

Asexual vs Sexual Reproduction

• Asexual Reproduction (NO

Diversity)

• Involves Mitosis

• 1 2 progeny

• Sexual Reproduction (PROVIDES

Diversity)

• Involves Meiosis

• 2 different cells (Mom/Dad) 1

offspring

• These reproductive cells are gametes

Chromosomes

• Humans have 46 chromosomes (2n)

• n=23

• 22 autosomes

• 1 sex chromosomes (X or Y)

• Somatic Cells (non-sex chromosomes) =2n (diploid)

• Gametes (sex chromosomes) =n (haploid)

Karyotype

• It is an ordered visual representation of the chromosomes in a cell

• It is based on length, centromere position, and staining pattern

• FISH (Fluorescent in situ hybridization)

• It uses fluorescent DNA probes that hybridize to chromosomal DNA

• Basically, it highlights the specific base pairs in different colors

Homologous Chromosomes

• They are similar but not identical chromosomes

• Same order of genes, Length is same, Position of centromere is the same

• But, the DNA is NOT identical

• Due to maternal and paternal contributions

• Ex: The same number chromosome from the mother and father

• Why have 2 copies?

• Increase diversity!

Meiosis Increases Diversity

• Overview

• 2n1n

• 1 set of all chromosomes in all gametes

• Helps with increased diversity

• Makes Haploid Gametes

• Independent Assortment of Chromosomes (each sister chromatid lines up randomly)

• Recombination “cross over” between homologous chromosomes

Meiosis

• Meiosis I

• Homologs line up at Metaphase (I)

plate

• Crossing over occurs

• Meiosis II

• Sister chromatids separate

• Very similar to mitosis

Meiosis I

• Prophase I

• Homologous chromosomes pair up

(maternal and paternal copies)

• Crossing over between homologs

occurs

• Increases diversity!!

• Nuclear envelope disassembles at end

• Metaphase I

• Homologs line up at metaphase plate

Meiosis I

• Anaphase and Telophase I

• Homologs are separated

• Cells are then divided

• Results of Meiosis I

• 2 daughter cells that are both 2n

• HOWEVER, they are both different

• Due to crossing over

• THEN goes Directly to Meiosis II

Meiosis II (Very similar to Mitosis)

• Prophase II

• Spindle assembles at right angle to

previous one

• Metaphase II

• Sister chromatids line up at metaphase

plate

• Anaphase and Telophase II

• Sister chromatids separated

• Cells divide

• Results of Meiosis II

• 4 cell gametes (n) all genetically

DIFFERENT

Compare and Contrast

Meiosis

• No S phase between I and II

• 2 cell divisions: cells are different

• Crossing over occurs

• Meiosis I homologs line up at plate

• Meiosis II sister chromatids line up

• 4 unique haploid daughter cells

Mitosis

• 1 cell division: cells are identical

• Sister chromatids line up at

metaphase plate

• 2 identical daughter cells