Cell Physiology

How the cell does what is does

Membrane Transport• There is fluid on each side of the plasma

membrane– Interstitial Fluid– Cytoplasm

• Solution- homogeneous mixture of two or more components– The substance found in largest amount is the

solvent.– The substance of a smaller amount is the

solute.

Fluids

• Intracellular Fluid (nucleoplasm and cytosol) – contains small amount of gases,

nutrients, and salts dissolved in water.

• Interstitial Fluid (around the cell)– Contains nutrients, hormones,

neurotransmitters, salts, and waste products

Selectively Permeable• A barrier that allows some substances

to pass through while excluding others.– Allows nutrients to enter but keeps other

substances outside the cell– Keeps cell organelles inside and allows

wastes to escape.

• The movement of substances across the plasma membrane occurs by:– Passive Transport– Active Transport

Burns• A cell will be selectively

permeable if it is unharmed. When cells have been damaged the plasma membrane will no longer be selective and will be permeable to anything.– When a victim is severely

burned, precious fluids are lost from the dead or damaged cells.

http://www.thedoctorwillseeyounow.com/articles/other/burns_23/12.jpg

Passive Transport- Diffusion• The process by which

molecules tend to scatter themselves through available space.– Controlled by kinetic

energy– Molecules will move from

an area of high concentration to an area of low concentration (concentration gradient).

– The speed of diffusion depends on the size of the molecules and the temperature.

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Diffusion and the Plasma Membrane

• The plasma membrane is a physical barrier to diffusion.

• Some molecules can passively diffuse across the membrane.

• Saves the cell a large amount of energy to transport important molecules.

Simple Diffusion

• Unassisted diffusion of solutes through the plasma membrane– Lipid-soluble molecules (fats, fat-soluble

vitamins, oxygen, carbon dioxide)– Small molecules (some small ions like Cl-)

• Simple diffusion of water is called osmosis– Pass through small pores in the membrane

Facilitated Diffusion

• Allows needed substances to enter the cell that are both insoluble and too large to fit– Example: Glucose

• A transport vehicle is required

Diffusion

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Diffusion

• Glucose and oxygen continually move into the cell– Lower concentration inside the cell

• Carbon dioxide moves out of the cell– Higher concentration inside the cell

Passive Transport- Filtration

• Water and solutes are forced through a membrane by fluid pressure (hydrostatic)– Pressure Gradient

• Pushes solute-containing fluid from high pressure area into a low pressure area

– Usually exerted by the blood– Kidneys use this method to produce

urine

Active Transport Processes• A cell uses ATP to move substances

across the membrane– Substances moved actively are too

large to fit though pores, insoluble in fatty portion of membrane, or must be moved uphill to the concentration gradient.

• Examples:– Solute Pumping– Bulk Transport

Solute Pumping

• Require protein carriers to bind to the substances to be moved across the plasma membrane

• Solute Pumps– Amino acids, some sugars, ad most

ions are transported by solute pumps– Move against the concentration

gradient

Sodium-Potassium Pump

• Simultaneously carries sodium ions out of and potassium ions into the cell.

• Important for nerve cells– More Na+ outside the cells than

inside– A pump is required to go against the

gradient

Sodium-Potassium Pump

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Bulk Transport

• Two Types:– Exocytosis– Endocytosis

Exocytosis

• Moves substances out of the cell• How cells actively secrete

hormones, mucus, other cell products and eject wastes.– Product is packaged by the golgi

apparatus into a small vesicle– The sac migrates to the membrane,

fuses, ruptures, and spills contents outside the cell.

Exocytosis

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Endocystosis• Uses ATP to engulf

substances into the cell– A vesicle is formed

around molecule– Detaches from the

membrane– Fuses with the lysosome

where is digested

• When large particles, bacteria, and dead body cells are digested by a cell it is called phagocytosis.– White Blood Cells

http://www.aamdsglossary.co.uk/white_blood_cells.jpeg

Endocytosis

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Bulk-phase Endocytosis

• Pinocytosis (cell drinking)• Plasma membrane creates a

vesicle of extracellular fluid

Cell Life Cycle• Series of changes

that a cell undergoes from the time it is formed until it divides.

• Consists of Two Major Periods– Interphase– Cell Division

Interphase• The longest phase

of the cell life cycle.

• The cell performs its normal functions:– Protein Synthesis

and other functions– This is the phase

when the DNA replicates itself (S phase)

http://www.eastcentral.edu/acad/depts/BI/interphase_animal_labels.jpg

Interphase

DNA Replication• Always precedes cell

division• The DNA helix uncoils into

two nucleotide strands.• Each strand now serves

as a template for building a new strand.– A always bonds with T– G always bonds with C

• Begin with one strand of DNA, ends with 2 identical strands that are half old and half new.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cell Division

• All body cells (except for reproductive cells) undergo cell division in two stages.– Mitosis- division of

nucleus– Cytokinesis- division

of cytoplasm

Mitosis

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Mitosis

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Prophase• Chromatin thread coil

into chromosomes• Made up of two

strands (chromatid) connected by a centromere.

• Centrioles replicate and move to opposite poles to form the mitotic spindle.

• The nuclear envelope breaks down.

http://www.eastcentral.edu/acad/depts/BI/animal_mitosis_labels.html

Prophase

Metaphase

• The chromosomes line up at the metaphase plate (the equator of the cell).

http://www.eastcentral.edu/acad/depts/BI/animal_mitosis_labels.html

Metaphase

Anaphase

• The centromeres split and the sister chromatids go to opposite ends of the cell.

http://www.eastcentral.edu/acad/depts/BI/animal_mitosis_labels.html

Anaphase

Telophase

• The reverse of prophase.

• Chromosomes uncoil into threadlike chromatin.

• The nuclear envelope reappears.

Telophase

Cytokinesis

• The division of the cytoplasm.• Begins in early anaphase and ends with

telophase.• A cleavage furrow appears over the

midline of the spindle.• Sometimes mitosis can occur without

cytokinesis:– Binucleate or Multinucleate cells (many

found in the liver)

The End of Mitosis

• The purpose of mitosis is to produce two identical daughter cells.

• When the cell has divided, the daughter cells will grow to the normal size of an adult cell before dividing again.

• Can take from 5 minutes to several hours to complete (normally 2 hours)

Cancer• Uncontrolled mitosis is the basis for tumors

and cancer• Increased cell division• Benign- local tumors that are surrounded by

a capsule• Malignant- nonencapulated masses that

grow relentlessly• Metastasis- malignant cells can spread via

the bloodstream• Carcinogens- cause mutations in DNA that

can lead to cancer

Cancer

Protein Synthesis• A gene is a DNA

segment that carries the information for building one protein or polypeptide.

• Genes are known as the blueprint of life.– They direct what

proteins are made.– They direct when

proteins are made.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Remember Proteins

• Enzymes are the biological catalysts of the body.– DNA regulates

cellular activities by specifying the structure of enzymes.

http://www.stanford.edu/group/blocklab/DNARNA.html

Triplet Code

• The exact sequence of bases in the DNA determines the protein to be made.

• A triplet refers to the three bases that calls for a particular amino acid.– Amino acids are linked together to form

proteins.– Triplets are linked together to form

genes.

The Role of RNA• DNA must stay inside the nucleus.

– It is too large to fit through the nuclear envelope.

• Proteins are made in the cytoplasm.– The genetic code must copied in smaller

pieces that can go to the ribosomes.• RNA decodes the genetic information,

carries it to the cytoplasm and directs the assembly of proteins.

The types of RNA

• There are three types of RNA– Messenger RNA (mRNA)

• Decodes the message and carries the code to the cytoplasm.

– Transfer RNA (tRNA)• Carries the amino acid to the ribosome.

– Ribosomal RNA (rRNA)• Directs the assembly of proteins.

Transcription• The genetic

information is transferred from DNA into mRNA.– Using the DNA as the

template, the complimentary RNA sequence is matched.

– A codon refers to the three letters of mRNA that code for a particular amino acid.

– Occurs in the nucleus.

http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/graphics/Transcription.01.GIF

Translation• The language of

nucleic acids is changed into the language of proteins.– Occurs in the

cytoplasm at the ribosomes.

– All three RNA’s are involved

– The mRNA codon is matched to the tRNA anticodon to put the amino acids in the correct order.

http://www.blc.arizona.edu/INTERACTIVE/DNA3/gencode.gif

Protein Synthesis and Genetic Disorders