Phys module 1

what common feature do all cells share?

- plasma membrane
- cytosol
- nucleus

what is the plasma membrane?

Thin membranous structure that encloses each cell

the barrier separates the cell contents from its surroundings

Selective control movement of molecules into and out of the cell

What is the plasma membrane composed of?

Lipid (fat) molecules (bilayer)

studded with proteins

What does the nucleus do?

- double-layered membrane
- houses DNA
- Directs protein synthesis

What is the endoplasmic reticulum?

- Fluid-filled membranous system (folded to increase surface area)

- A protein and lipid producing factory

- contains Rough and Smooth ER

What is the rough ER?

- Studded with ribosomes
- synthesizes proteins to be secreted to the exterior or to be incorporated into plasma membrane or other cell components

What is the smooth ER?

- makes lipids
- packages the secretory product into transport vesicles, which bud off and more to the Golgi complex

What is the Golgi complex?

- Sorts protein
- Consists of stacks of flattened, slights curved, membrane-enclosed sacs
- closely associated with the ER
- Modifies, packages and distributes newly synthesized proteins

Why is Golgi complex located near the ER?

Because the transport vesicles fuse to the Golgi to allow Golgi to sort proteins

it sorts it into vesicles which are directed to go to a specific location

What are lysosomes?

- digestive system of the cell: destroy foreign substances and cellular debris
- small, membrane-enclosed, degradative organelles
- break down organic molecules with powerful hydrolytic enzymes

What are peroxisomes?

- membrane-enclosed sacs containing oxidative enzymes (uses o2 instead of water)
- Detoxify various wastes produced within the cell or foreign toxic compounds that have entered the cell
(eg. alcohol)

Where are peroxisomes abundant?

liver

What are centrioles?

- A pair of cylindrical structures at right angles to each other
- form and organize microtubules during assembly of the mitotic spindle during cell division
- form cilia and flagella (Lining of the trachea and sperm cells)

Where is mitochondria most abundant?

Muscle cells

What is the mitochondria?

- rod-shaped or oval structures about the size of bacteria
- enclosed by a double membrane
- The inner membrane forms a series of infoldings called cristae
- cristae projects into an inner cavity filled with a gel-like solution known as the matrix

Where is the cristae located in the mitochondria?

Inner membrane

What is the function of the mitochondria?

Creates ATP

Contains enzymes for the citric acid cycle and ETC

What is the structure of microtubules?

- Long, Slender, hollow tubes composed of tubulin molecules

- Maintain asymmetric cell shapes and coordinate complex cell movements
( highways for transport of secretory vesicles within cells)

What is the function of microtubules?

- Main structural and functional component of cilia and flagella
- Position cytoplasmic organelles (ER, Golgi complex, lysosomes, and mitochondria)
- assemble into the mitotic spindle

Why is the mitochondria close to the microtubule?

To allow energy for movement

Structure of microfilaments?

- Smallest elements of the cytoskeleton (actin & myosin)
- intertwined helical chains of actin molecules; microfilaments composed of myosin molecules also present in muscle cell

Function of microfilaments?

Play a vital role in various cellular contractile systems, including muscle contraction and amoeboid movement (EBC or fibroblast); serve as a mechanical stiffener for microvilli

What are intermediate filaments?

- Irregular, threadlike proteins
- help resist mechanical stress

eg keratein

Where are intermediary metabolism enzymes and what is there function?

Dispersed within the cytosol

Facilitate intracellular reactions involving degradation, synthesis and transformation of small organic molecules

What are transport, secretory and endocytic vesicles?

Transiently formed, membrane-enclosed products synthesized within or engulfed by the cell

Transport or store products being moved within, out or into the cell

What are inclusions?

Glycogen granules, fat droplets

Stores excess nutrients
(glucose and lipids --> liver and muscle have more glucose stores)

What is intermediary metabolism?

refers collectively to the large set of chemical reactions inside the cell that involve the degradation, synthesis and transformation of small organic molecules such as simple sugar, amino acids, and fatty acids

Occurs in the cytosol and involves thousands of enzymes

What is anabolism?

Synthesis build-up (building up)

What is catabolism?

degradation breakdown (breaking down)

Where does intermediary metabolism occur?

Cytosol

How is the ATP produced in the cell?

1) Creatine phosphate (CP)
2) Anaerobic Glycolysis
3) Aerobic metabolism

Most ATP production: Glycolysis. (anaerobic and aerobic), decarboxylation of pyruvate, the tricarboxylic acid cycle (TCA) and the ETC

What does substrate level phosphorylation of ADP use?

Creatine Phosphate (CP)

What is the first source of energy during muscle contractile activity?

Creatine phosphate (CP)

Where is creatine phosphate (CP) stored?

Cytoplasm

What contains high phosphate bonds?

ATP and CP

How is creatine catalyzed?

The enzymatic reaction catalyzed by the creatine kinase

THIS REACTION IS REVERSIBLE

(Creatine phosphate gets broken down by creatine kinase with ADP to create ATP to create ATP = More energy)

What is the point of the creatine phosphate system?

Since there is a limit of how much ATP a cell can produce (because it runs out of ADP - around 5mM), creatine phosphate is there to provide extra energy, as it can be catalyzed to create more ATP

How much CP and ATP are in skeletal muscle at rest?

5x more CP than ATP - most of the stored energy is the form of CP

What happens to the CP and ATP during skeletal muscle contraction?

CP will replenish the used ATP

CP levels change faster than that of ATP

How many reactions are involved in glycolysis?

10 sequential reactions that break down glucose

How is glucose broken down in glycolysis?

10 reactions break down glucose (6 carbon molecule) into two pyruvates (3 carbon molecules)

Some energy from the broken chemical bonds of glucose is used directly to convert ADP into ATP ( net 2 ATP produced)

What is McArdle disease?

The absence of enzyme involved in the first step of glycogen-to-glucose conversion
(No problem with glycolysis itself)

Glycolysis is not very efficient in terms of energy extraction, only producing 2 ATP and 2 NADH per molecule of glucose (anaerobic). - most of the energy contained in the glucose molecule remains "locked" in the chemical bonds

How many steps of reaction is pyruvate decarboxylation?

1 step reaction

What happens during pyruvate decarboxylation?

- pyruvate enters the mitochondrial matrix
- catalyzed into Acetyl CoA (a 2-carbon molecule) - removes one carbon molecule (from CO2)

Where does Acetyle CoA go after pyruvate decarboxylation?

Enters into TCA cycle aerobic metabolism

What happens to CO2 during pyruvate decarboxylation?

Eliminated via cardio-respiratory system

How many reactions are involved in the citric acid cycle?

8 separate reactions directed by the enzymes from the mitochondrial matrix

Where does the citric acid cycle happen?

Mitochondrial matrix

What happens during the citric acid cycle?

1) Two carbons (2C) are sequentially removed from the 6C citrate molecule --> converted back to the 4C oxaloacetate, ready to accept a new Acetyl-CoA

2)These 2C are converted into 2 molecules of CO2

3) These 2 CO2 as well as the one produced during the pyruvate decarboxylation, pass out of the mitochondrial matrix --> Out of the cell--> Blood

4) The O2 used to form these CO2 molecules is coming from these molecules involved in the cycle, not from the free O2 supplied from breathing

5) Hydrogen atoms are also removed (four steps). This is the key point of the citric acid cycle! These H will then enter the Electron Transport Chain (ETC).

6) One ATP molecule is indirectly produced. The processing of ACoA releases energy --> Linkage of inorganic phosphate to Guanosine diphosphate (GDP) --> GTP

7) 1 Glucose 2 Acetyl-CoA 2 turns of the citric acid cycle 2 ATP = Limited energy profit!

What are the hydrogen carrier molecules?

Nicotinamide Adenine Dinucleotide (NAD+) --> NADH

Flavine Adenine Dinucleotide (FAD) --> FADH2

What carries high-energy molecules?

NADH & FADH2

How many ATP is created per TCA?

2

How does GDP create energy?

ADP + GTP = ATP + GDP

Reversible reaction

Where is most of the energy stored in the ETC?

Most of the energy is still stored in H (they contain electrons at high energy levels)

Where is the ETC located?

inner membrane of mitochondria

Where are the electrons extracted from in the ETC?

NADH and FADH2

Where is most the ATP produced?

ETC (28 ATP produced)

What is the final electron acceptor?

Ultimately, electrons passed to O2

What is oxidative phosphorylation?

The electrons are passed to O2

Phosphorylation of ADP to ATP

What happens to the NADH and FADH2 in the ETC?

They are converted back into NAD+ and FAD
- free to pick up new H molecules
- they represent the link between the TCA and ETC

How much ATP per NADH?

2-3 ATP (2.5 on average)

How much ATP per FADH2?

1-2 ATP (1.5 ATP on average)
- always one less ATP than NADH

What happens to the high-energy electrons in the ETC?

The high-energy electrons fall to successively lower energy levels as they are transferred from carrier to carrier through the ETC

What happens to electrons as they move through that ETC?

As electrons move through the ETC, they release free energy

part of the released energy is harnessed to transport H+ from the matrix into the intermembrane space at Complexes I, III, and IV

Does FADH2 interact with complex 1?

No

How does ATP synthase make ATP?

ATP synthase turns to make ATP (catalyzes using the energy from the H+ gradient across the membrane)

As a result, H+ ions are more heavily concentrated in the intermembrane space than in the matrix
- this H+ gradient supplies the energy that drives ATP synthesis by ATP synthase

If oxygen is limited or unavailable, what is pyruvate converted into?

Lactate

What is the condition called when oxygen is unavailable?

Anaerobic

does the degradation of glucose proceed beyond glycolysis?

No the degradation of glucose does not proceed beyond glycolysis

Is more energy produced aerobically or anaerobically?

Aerobically

What are other sources of ATP production?

Fatty acids and proteins
- enter at the Acetyl coA step

Does lactic acid enter the TCA?

no

How many layers does the plasma membrane have?

2

Wha do the layers of the plasma membrane contain?

Phospholipids

What is the purpose of the plasma membrane?

Separates the extracellular and intracellular compartments/fluids (ECF and ICF)

Is the head of the phospholipid positively or negatively charged?

Negatively charged and likes water (polar)

Is the tail of the phospholipid positively or negatively charged?

uncharged and hates water (nonpolar)

What happens if the cell loses the integrity of the plasma membrane?

It will die

What are the most abundant membrane lipids?

Phospholipids and some cholesterol

What does the fluid mosaic model refer to?

Refers to the membrane fluidity and the ever-changing mosaic pattern of the proteins embedded in the lipid bilayer

What are channel proteins?

Allows very small water-soluble molecules (ions) through

eg Na+ channel

Why can't ions just go through the plasma membrane since they are small?

Ions are charged and have a repelling force on the bilayer, which is why they need to go through the channel proteins

What are carrier molecules?

transfer of specific substances; glucose

What are docking-marker acceptors?

for secretory vesicles and the exocytosis process

What are the three different means that cells are held together by?

1) Cell Adhesion Molecules (CAMs) - membrane proteins that allow cells to mold onto each other

2) The extracellular matrix (ECM) - Allows it to be elastic

3) Specialized cell junctions

what is the extracellular matrix?

The ECM is an intricate meshwork of fibrous proteins embedded in a watery, gel-like substance (aka Interstitial fluid) composed of complex carbohydrates

What is interstitial fluid?

Provides a pathway for the diffusion of nutrients, wastes, and other water-soluble traffic between the blood and tissue cells (allows space so ions can move)

What are the three major types of protein fibres woven through the gels?

1) Collagen
2) Elastin
3) Fibronectin

What is collagen?

Forms cable-like fibers (provides strength to tissue)

Tensile strength

(most abundant protein in the body - 1/2 of total body protein by weight)

What is elastin?

Rubber-like protein Fiber
- stretching and recoiling (eg lungs)

What is fibronectin?

Promotes cell adhesion
- holds cells in position
(reduced levels are linked to tumor metastasis)

How do CAMs provide tissue cohesion?

CAMs provide some tissue cohesion as they "Velcro" adjacent cells together

What are the three types of specialized cell junctions that cells are directly linked by?

1) Desmosomes (adhering junctions)

2) Tight junctions (Impermeable junctions)

3) Gap junctions (communicating junctions)

Desmosomes

adhering junctions

Tight Junctions

Impermeable junctions

Gap junctions

communicating junctions

What do desmosomes do?

- act like 'spot rivets' that anchor together two adjacent but non-touching cells

- most abundant tissues that are subject to considerable stretching (skin, heart, uterus)

- They are the strongest cell-to-cell connection



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What do tight junctions do?

- Adjacent cells firmly bind together at points of contact to seal off the passageway between the two cells

- Found primarily in sheets of epithelial tissue such as those that cover the body and line internal cavities
(e. g. epithelial sheet lining the digestive tract separates the food and potent digestive juices within the inner cavity (lumen) from the blood vessels on the other side)

- Impermeable barrier

What do Gap junctions do?

A gap exists between adjacent cells, which are linked by small, connecting tunnels (formed by connexons)

Communicating junctions (permits small, water- soluble particles to pass between the connected cells but precludes passage of large molecules)

Abundant in cardiac muscle and smooth muscle (allow movement of ions to transmit electrical activity synchronized contraction of a whole muscle mass)


Forms tunnels made out of proteins to allow small molecules to go through - most abundant in the heart

What are the 2 properties that influence whether a substance can permeate the plasma membrane without any assistance?

Relative solubility of the particle in lipid
- uncharged or nonpolar molecules --> highly lipid soluble --> easily permeable

size of particle