Structure & Function of Cells (2)

Based on the book 'Human Biology' by Michael Johnson

Name the main parts a prokaryotic cell consists of

Plasma membrane

Cytoplasm

* fluid within membrane

Cell wall

Genetic material

Bacterial cells are prokaryotic

Name the main parts an eukaryotic cell consists of

Plasma membrane

Nucleus

* membrane bound information center

Cytoplasma

Organelles

* membrane bound structures with specialized functions

All human cells are eukaryotic

What’s the main difference between prokaryotic & eukaryotic cells?

Prokaryotic

* primitive
* no organelles
* no nucleus
* no distinct structures
* \

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Eukaryotic

* no cell wall
* ‘incorporation of prokaryotic cells in one big cell’
* cytoplasm enclosed by flexible plasma membrane

How does (eukaryotic) cell structure reflect cell function?

Eukaryotic cells remarkably similar, but structural differences

* **muscle cells**: contain many organelles providing energy needed for muscle contraction
* **nerve cells**: long & thing to carry impulses over distance

Small size = efficient

Why is the small size of cells efficient?

Small cells have higher surface-to-volume ratio

→ Promotes efficiency in

* acquisition of nutrients
* disposal of water

Which aspects of the cell can affect surface area & volume?

Cell size

Plasma membrane shape

What are the 3 different types of microscopes & what can be seen with them?

Light microscope

* magnifies up to 1K x
* used to view living specimens

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Transmission electron microscope

* magnifies up to 100K x
* without light
* can reveal internal details of cell structure

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Scanning electron microscope

* magnifies up to 100K x
* without light
* provides 3D view of cell surface

Name all the parts of a typical animal (eukaryotic) cell

Nucleus

Ribosomes

Endoplasmic reticulum (rough & smooth)

Golgi apparatus

Vesicles

Mitochondria

Cytoskeleton

Cilia

Flagella

Centrioles

Plasma membrane

What is the function of the nucleus & what are the structural features?

Function

* contains genetic information of the cell
* controls all activities of the cell

\
Structural features

* double-layered nuclear membrane
* nuclear pores
* chromosomes/chromatin
* nucleolus

What’s the function of ribosomes & how does their location reflect that?

Responsible for protein synthesis

\
Location

**Free**: floating in cytoplasm

* these ribosomes synthesize proteins for immediate use in the cell

**Bound**: attached to outer surface of ER

* these ribosomes synthesize proteins that will be transported to other organelles or exported from the cell

What 2 types of endoplasmic reticulum (ER) are there & what’s their function?

= Manufacturing center

Highly folded membranous network

\
Rough ER

* has ribosomes on surface
* Manufactures proteins, particularly those that’ll be secreted from the cell

\
Smooth ER

* no ribosomes on surface
* lipid synthesis, incl. synthesis of some hormones
* packages proteins & lipids for delivery to Golgi apparatus

What does the Golgi apparatus do?

**Refines** synthesized products

**Packages** products into vesicles

**Ships** packaged products to other locations within cell or to the cell membrane for export

What are vesicles?

Membrane-bound storage & shipping containers

What are the 4 types of vesicles & what do they contain?

**Secretory** vesicles

* contain products destined for export from the cell

**Endocytic** vesicles

* contain substances imported from the external environment

**Peroxisomes**

* contain enzymes that detoxify wastes produced by the cell

**Lysosomes**

* contain digestive enzymes

What’s the function of the mitochondrion & how is it structured?

Provides energy

* ‘power plant’ of the cell

Number of mitochondria within cell varies with cell’s energy requirement

Site of cellular respiration

* utilizes O2
* produces CO2

Generates ATP

\
Structure

* surrounded by double membrane
* inner membrane is highly folded

What are the sources of energy?

Fat

* triglycerides
* **long-term** energy storage in animals

\
Glycogen

* carbohydrate storage
* **short-term** energy storage in animals
* stored in muscle & liver cells

What structures give cells support & enable movement?

Cytoskeleton

* internal scaffolding helps maintain cell shape

Enable movement

* cilia
* flagella
* centrioles

What is the cytoskeleton made of & what are the functions?

Microtubules

* tiny hollow tubes of protein

Microfilaments

* thin solid fibers of protein

\
Microtubules & -filaments form framework that supports cell

Cytoskeleton also supports & anchors other cellular structures

* some proteins from membrane bound to cytoskeleton

How are cilia, flagella & centrioles structured & what are their functions?

Cilia

* short, many
* found on cells lining airways

\
Flagella

* long, single
* similar internal structure to cilia
* enable spermatozoa to swim

\
Centrioles

* short rod-like microtubular structures near nucleus
* play important role in cell division

What’s the function of the plasma membrane?

Separates cell from its environment

Selectively permeable

* permits movement of some substances into & out of cell
* blocks others

Enables transfer of information between environment & cell

How is a plasma membrane structured?

= Lipid bilayer

* **phospholipids**: polar head & nonpolar tail
* **cholesterol**: makes membrane more rigid
* **proteins**: provide means of transport through membrane
* **carbohydrates**: recognition patterns for cells & organisms, provide communication system for outside of cell

Non-rigid

Fluid mosaic

What types of transport are there for molecules crossing the plasma membrane?

Passive transport: cell doesn’t need to expend energy for this

* diffusion
* osmosis

\
Active transport: cell must expend energy

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Bulk transport: involves membranous vesicles to move larger substances

* endocytosis
* exocytosis

What is passive transport & how does it work?

Transports substance without having to expend energy

Relies on diffusion

High concentration → low concentration

‘Down’ the gradient

What is diffusion?

Movement of molecules from e region of high concentration to a region of low concentration

What is osmosis?

Diffusion of water across a selectively permeable membrane

Water moves from an area of low solute concentration to an area of high solute concentration

What is osmotic pressure?

Fluid pressure required to exactly oppose osmosis

What are the 3 forms of passive transport?

Directly through lipid bilayer

* small uncharged nonpolar molecules

Through protein channels in bilayer

* some always open, others ‘gated’

Facilitated transport

* membrane transport protein changes shape & transports molecule through bilayer
* highly specific
* eg. glucose

How does active transport work?

Moves substance from an area of lower concentration to an area of higher concentration

* transported substance moves against concentration gradient

What does active transport require?

Membrane protein (transporter) & ATP or other energy source

What is bulk transport used for?

Used to move larger molecules

What is endocytosis?

Brings substances into cell

* as substance enters, it’s surrounded by a membrane, forming a membrane-bound vesicle

What is exocytosis?

Expels substances from the cell

* substance contained within membranous vesicle, which then fuses with the membrane, releasing the substance to the external environment

How is information transferred across plasma membrane?

Receptor proteins span membrane

* required for transmission of information to & from cell

Receptor sites (on receptor proteins) interact specifically with signal molecules

Change is triggered within cell as result of binding of signal molecule to receptor site

Different cell types have different receptor proteins

What does the Sodium-Kotassium pump do?

Expels unwanted ions, stockpiles needed ones & maintains cell volume

ATP is used to expel 3 Na+ for every 2 K+ brought into the cell

What is happening when the cell volume is increasing?

More water in cytoplasm, accomplished by **decreasing** pumping & allowing more sodium inside cell

What is happening when the cell volume is decreasing?

Less water in cytoplasm, accomplished by **increasing** pumping & expelling more sodium ions

What else maintains cell volume?

Isotonic extracellular fluid

What is tonicity & what are the different types?

= Relative concentration of solutes in 2 fluids

Isotonic

Hypertonic

Hypotonic

What are characteristics of isotonic extracellular fluids?

Extra- & intracellular solute concentrations are **equal**

Cells maintain normal volume

Regulatory mechanisms maintain extracellular fluid that is isotonic with intracellular fluid

What happens to the cell volume when extracellular fluids are HYPERtonic?

Extracellular solute concentration **higher** than intracellular solute concentration

Water will diffuse out of cell

Cell may shrink & die

What happens to the cell volume when extracellular fluids are HYPOtonic?

Extracellular solute concentration lower than intracellular solute concentration

Water will diffuse into cell

Cell may swell & burst

That’s why we don’t inject people with pure water

What is the metabolism?

Sum of all chemical reactions in an organism

What are the 2 types of metabolic pathways?

Anabolism

* larger molecules assembled from smaller ones
* requires energy (ATP input)

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Catabolism

* larger molecules broken down
* releases energy (ATP output)

What do chemical reactions/metabolical activities require?

Specific enzyme

A lot of energy

* often provided by catabolism of ATP
* ATP

What is glucose used for? Link this with ATP

Provides cell with energy

Energy in glucose used to generate ATP

* 1 glucose molecule → 36 ATP

Absence of glucose → other carbohydrates, fats & proteins can be catabolized to generate ATP

ATP = more readily used ‘pocket change’ form of energy

Glucose & other fuel molecules must be ‘cashed in’ for ATP

ATP can then be used to do cellular work

What is cellular respiration?

Breakdown of glucose in the presence of **oxygen** to yield ATP

Cellular process that uses O2 & produces CO2 in process of making ATP

What are the 4 stages of cellular respiration?

1. Glycolysis
2. Preparatory step
3. Citric acid cycle
4. Electron transport system

What happens during glycolysis?

Occurs in **cytoplasm**

Series of 10 reactions that **split** glucose into 2 molecules of **pyruvic acid (pyruvate)**

Requires investment of 2 ATP; 4 ATP produced

* netto ATP yield: 2

High-energy electrons & hydrogen ions removed & picked up by coenzyme NAD+

→ NADH formed

Later in process, NADH used to generate additional ATP

What happens during the preparatory step?

Pyruvate

* enters mitochondria
* converted to **acetyl group** & CO2

High-energy electrons & hydrogen ions removed & picked up by coenzyme NAD+

→ NADH formed

Acetyl group joined to coenzyme A to form **acetyl CoA**

Acetyl CoA will enter citric acid cycle

What happens during the citric acid cycle?

Occurs in **mitochondria**

Cyclic series of **8** reactions which **break down acetyl CoA**

Molecule that accepts acetyl CoA regenerated at the end of 1 full turn of the cycle

High-energy electrons extracted to form **NADH & FADH2**

Produces **2 ATP & 4 CO2** per glucose molecule

What does the electron transport system do?

Located in **inner mitochondrial membrane**

Takes electrons from NADH & FADH2

Movement of electrons from 1 electron carrier to the next **releases** energy to **generate ATP**

Final electron acceptor: O2

* forms water upon receiving electrons & hydrogen ions
* more hydrogen ions on one side = diffusion process

ATP generated by ATP **synthase enzyme**

* diffusion force by enzyme & stream of hydrogen ions used to produce ATP

What’s the electron transport system process also known as?

Oxidative phosphorylation

How many **different enzyme-catalyzed reactions** take place during the energy production from glucose?

Over 20

What are the additional energy sources?

__Fats__

* 78% of total energy reserves
* **triglycerides** have **twice** the energy of carbohydrates

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__Proteins__

* 21% of total energy reserves
* same amount of energy as carbohydrates

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__Glycogen__ (storage form of glucose)

* 1% of total energy reserves
* can be quickly catabolized to glucose, which then participates in cellular respiration

What are the functions of **anaerobic pathways**?

Make energy available **without** oxygen

* cellular respiration cannot continue without O2
* happens when blood can’t catch up with intense labor
* glycolysis will continue, pyruvate will build up
* **lactic acid** buildup in muscles → burning sensation → muscle ache
* 2 ATP produced per glucose molecule

When O2 available, lactic acid metabolized aerobically