Cells. Structure, Function and Homeostasis

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Cells

Structure, Function and

Homeostasis

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Characteristics of Cells

• Basic unit of life

– anything alive is made of cells

• Plasma membrane (skin) that separates them from the environment.

• Skeletonsfor protection & support (proteins)

• Move (via proteins)

• Communicate (via hormones)

• Harness & use Energy (produce enzymes, heat)

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Cells are small

• 10 – 100µm

• Small to minimize energy needs…

• But large enough to house specialized

organelles and to minimize heat loss

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Size determines rate of life

• Large enough to house organelles needed to eat, grow, reproduce • Small enough that

very

little

energy & time is needed for

transport of nutrients & waste

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Simple,

Prokaryotic

cells

• Lack nuclei (have nucleoid region), few organelles

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Bacteria & Archaea - Prokaryotes

• Wildly diverse

– ~ 500 species in your mouth alone

• Abundant (numerous)

– 1012 on your skin; 1014 in G. I. tract; 1 teaspoon of soil contains

billions

• Ubiquitous

– O2-free mud; salt flats; boiling hot springs; bedrock 1500 m deep; 10 km beneath ocean’s surface; 0˚- 121˚C

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Eukaryotic Animal cell

• Endomembrane System

– Nucleus

– Smooth & Rough Endoplasmic Reticulum – Golgi Apparatus – Lysosomes ** – Plasma membrane • Ribosomes • Peroxisomes • Mitochondria • Centrioles ** • Flagellum ** • Cytoskeleton

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Eukaryotic Plant cell

• Vacuole • Cloroplasts (& other plastids: amyloplasts) • Cell wall

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Nucleus: Control center (brain)

Cytoplasm - organelles,

free proteins, ions (guts)

Cell (plasma) membrane -

barrier between inside and outside (skin)

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Questions for the cell

• What structure controls which proteins, lipids & RNA are produced & when?

• Where do cells get Energy? Which structures harness it?

• What structures move stuff around the cell? • Where are proteins and lipids built?

• How do cells move molecules in and out?

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Nucleus: Control center

• Holds DNA, and “machinery” for replicating DNA and transcribing it into proteins • Surrounded by nuclear envelope (phospholipid

bilayer) •Nuclear pores •Chromatin

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• Genetic code =

DNA, coiled into chromosomes • Chromosomes? – Hypercoiled chromatin • Chromatin? – DNA coiled around protein

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Where and what is the

cytoplasm

?

• Between cell membrane & nuclear

membrane

• Consists of:

– Cytosol: intracellular fluid (mostly H20, ions & buffering proteins)

– Organelles: structures with specific functions; suspended in cytosol

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Ribosomes

• Organ of protein

synthesis

• Made of 2 subunits; each made of rRNA + protein • Two varieties

– Free ribosomes: produce proteins that travel to nucleus

– Fixed ribosomes: produce proteins for export to

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Endoplasmic Reticulum (ER)

• Network of membranes connected to nuclear envelope

• 4 major functions

1. Synthesis (pro, carbs, lipids) 2. Storage 3. Transport 4. Detoxification • Two types 1. Smooth 2. Rough

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Smooth ER (SER)

• Why is it called smooth?

• Responsible for the synthesis and

storage of:

– Phospholipids and cholesterol for

maintenance & growth of cellular membranes (ER, nucleus, Golgi apparatus (GA)) What type of molecules?

– Steroid hormones: estrogens and androgens – Triglycerides in liver and fat cells

– Glycogen in skeletal muscle and liver cells

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Rough ER (RER)

• Workshop

• Site of

protein

synthesis

(it has fixed ribosomes!!) Some chemical

modification.

– Polypeptide chains

migrate into cisternae, assume tertiary

structure + additional modification

• Ships proteins to GA via transport vesicles

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Golgi Apparatus

• Packing & shipping depot • Consists of 5-6

flattened membranous disks (cisternae)

• Functions

– Modifies (adds parts) & packages secretions

– Renews cell membrane

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• Produces 3 type of vesicles:

1. Secretory - exocytosis

2. Membrane renewal – replacement & remodeling

3. Lysosomes - “Primary” contain inactive digestive enzymes

Functions of GA

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Abnormal lysosomes

• Lack, or have malfunctioning enzymes

– Normal cell products accumulate & stifle (suffocate) cells

• Tay-Sachs disease

– Lysosomes lack enzymes that break down lipids in nerve cells

• Pompe’s disease

– Lysosomes lack hydrolytic enzyme that splits glycogen

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The endomembrane system

allows membrane flow

• Phospholipid bilayer is maintained!

• Nuclear envelope  continuous network of SER & RER  transport vesicles  Golgi Apparatus  secretory vesicles  cell membrane

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Peroxisomes metabolize

dangerous material

• Functions:

– Absorb and breakdown fatty acids and nucleic acids - produces H2O2 (danger!)

– Convert free radicals to H2O2

– Coverts H2O2 to harmless H2O and O2, using

catalase

• Produced by division of existing

peroxisomes

• Contain digestive enzymes;

produced @ free ribosomes

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Concept Check

a) The ribosomes on the rough endoplasmic

reticulum are analogous to a production line in a

factory.

b) The golgi apparatus is

analogous to the packaging and shipping department. c) The nucleus is analogous to

management offices. d) All of the above.

The cell is sometimes described as a protein factory. Using the cell-as-factory analogy, which of the following accurately describes the

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Mitochondria harness energy!

• “powerhouse” of the cell…makes ATP

• Double membrane • Number per cell

varies with

metabolic activity

(0% volume of RBC, 20% volume of liver cell)

• Aerobic respiration • Anaerobic resp.

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Chloroplasts make food!

• Photosynthetic

organisms (Autotrophs) • Sunlight + CO2 + H20 =

sugars

• Stroma: tubules & membranous disks

• Grana: stacks of disks; membranes chock full of chlorophyll, which traps solar energy

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Structure of cell membrane

• Contains lipids, proteins and

carbohydrates

– Lipids

• Phospholipids; Cholesterol; Glycolipids

– Proteins

• Integral; Peripheral

– Carbohydrates

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Cell Membrane Functions

Physical isolation

-

separates inner and

outer environments

Sensory receptor

-

receptor proteins

sense changes in external environment

(encrusted with peripheral nerves)

Regulates exchange

with the

environment -

membrane channel proteins + carrier proteins

Structural support

-

intercellular protein

Figure

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References

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