Cell Form and Function

Dr. AndersonGCIT

Cell Diversity • Connect tissues and transportation – blood, epithelia

• Body movement – muscles (smooth, striated, cardiac)

• Storage – adipose (fat cells), hepatocytes

• Immune Function – WBC’s

• Communication and information processing – nerve cells

• Reproduction – Egg and sperm cells

Cell Membrane • Keeps the cell contents separate from the

environment (extracellular fluid)

The Fluid Mosaic Model• Cell membrane is made of a phospholipid

bilayer– Self-assembling!– Extremely thin

Non-polar tails

Polar Heads

Polar Heads

Polar Heads are phospholipids and the non-polar (hydrophobic) ends are fatty acids

Outside of cell – interstitial fluid

Inside of cell – cytoplasm

Membrane ProteinsFacilitate the transport of material across the membrane

Integral (trans-membrane) protein – facilitates transport into and out of the cell

Membrane Proteins

Peripheral protein – can be attached to inside or outside layer of cell membrane

• Act as enzymes (outside and inside) or serve to move or support the cell (inside)

Glycoproteins – sugar-bound proteins

Glycoproteins – make up a sugary coat that envelops the cells called the glyco-calyx or “sugar cup”

The Glycocalyx

• The carbohydrates on the cell surface provide a way for some cells to recognize each other– Sperm and egg– WBC and bacteria or other pathogens

Membrane Junctions

• Bind cells together – glycoproteins act as adhesive

• Cell membrane structure – tongue-and-groove

• Specialized Junctions – – Tight junction– Desmosomes– Gap Junctions

Special Membrane Junctions• Tight Junctions – proteins in the cell membranes

that bind cells together– Makes sure nothing passes between cells

• Desmosomes - small points of connective proteins that anchor cells together– Found in cells subject to heavy pulling forces

• Gap Junctions – an open junction between adjacent cells– Permits chemical communication (transport) between

cells

Membrane Transport

• Interstitial Fluid – extracellular fluid largely derived from blood, but acellular– Amino acids, wastes, electrolytes, sugars, etc.

• Cells need to hold a balance of these solutes between their inside and outside environments

• How is this done?

Membrane Permeability

• Membranes only allow passage to certain molecules, or only permit movement in one direction

• Selectively Permeable – only certain molecules can pass

Active Transport

• ATP is used to drive the concentration gradient across the cell membrane 1. Primary – ATP changes the shape of membrane

proteins to shuttle specific materials across2. Secondary - uses stored potential energy from

primary transport to move substances3. Vesicular – vesicles “gulp” materials from outside

the cell by pinching off a bubble from the cell membrane

ELMO

• Review Pages 74-75 in textbook to explain prior slide in more detail

Vesicular Transport

• Endocytosis – cell ingests materials via vesicles– Receptor mediated

• Exocytosis – cell expels material into the environment via vesicles

• Phagocytosis?

Plasma Membrane – Resting Potential

• Many cells work using electrical energy which is derived from ion separation– Muscle cells, nerve cells, etc.

• How is this accomplished?

Electric Membrane Potential

- --

- --

- - ---

+ ++

K+

++

++ ++

Anions (negatively charged proteins build up)

K+

pump

Cations (postively charged ions (K, Na) build up)

Cytoplasm

• The material between the cell membrane and the nucleus

• Three major elements– Cytosol– Organelles– Inclusions

Cytosol

• Liquid part of the cytoplasm

• Consists of mostly water, but also dissolved substances such as– Salts– Sugars – proteins,– Etc.

Cytoplasmic Organelles

• Carry out cellular metabolic processes

• Specific to the kingdom of living things (e.g. chloroplasts are only found in plants)

Mitochondria

• Powerplants of the cell

• Breaks down food and uses this energy to form ATP from ADP (cellular respiration)on inner membranes (cristae)

• Have their own DNA, RNA and ribosomes– Huh?

Ribosomes• Made of two RNA-protein

subunits that work together to synthesize proteins (protein translation)

• Two types– Free ribosomes – make

soluble proteins– Membrane-bound

organelles – make proteins for packaging or export

Endoplasmic Reticulum (ER) • Membranes in the cytosol that are

continuous with the nuclear membrane

• Rough ER – lined with ribosomes that produce proteins that are secreted from cells, also make new phospholipids and intracellular membranes

• Smooth ER – Embedded with enzymes that catalyze the metabolism of proteins, fats, hormones, toxins and glycogen

Golgi Apparatus

• Stacks of membranous sacs in the cytosol

• Used to concentrate, modify and/or package proteins and lipids made by the rough ER.

• Packaged proteins are called vesicles are sent into the cytosol or outside of the cell (exocytosis)

Lysosomes

• Contain activated enzymes that may be capable of digesting all type of biological molecules

• The membrane-bound lysosomes contain these dangerous substances, preventing cell damage

Peroxisomes

• Contain extremely reactive oxygen species (ROS) that are used to detoxify certain poisons such as alcohol

• Also destroy free radicals – highly reactive waste products of metabolism that can disrupt cell processes– In which cells might these be found?

Cytoskeleton

• Consists of rods made of tubulin that run through the entire interior of the cell– Microtubules– Microfilaments– Intermediate

filaments

Cytoskeleton Components• Microtubules– Determine cell shape and influence organelle dstribution

• Microfilaments – A “web” of these filaments attach to the inner surface of

the cell membrane and give the cell strength. Also helps change cell shape during mitosis/meiosis

• Intermediate Filaments– Give the cell tensile strength by attaching to desmosomes

Centrosomes and Centrioles

• Centrosomes – serve to anchor microtubules and provide attachment points during activities such as cytokinesis, alignment of chromosomes during mitosis (mitotic spindle)

Cilia

• Relatively short extensions of tubulin that cover cells

• Enables cells to move through their environment, or move the liquid environment around themselves

Flagella

• Long extensions of tubulin protein used for propulsion

• Many microorganisms possess flagella

• Only human cells that possess flagella are sperm cells

Inclusions

• Chemical substances that may or may not be present, depending on the cell type. – Pigments– Crystals– Vacuoles– Etc.

The Nucleus

• The nucleus is a membrane-bound organelle that serves as the central control system of the cell

• All instructions for the cell’s processes are carried on genes that can be found within the DNA housed inside the nucleus

Nucleus

• Nuclear Envelope – double layered membrane that surrounds the nucleus– Outer Layer – continuous with ER– Inner Layer – lined with lamina, filaments that

hold the nuclear shape– Nuclear pores penetrate both layers, allowing

some molecules to flow into and out of the nucleus

Nucleus

• Nucleoli – dark-staining regions in the nucleus where ribosomal RNA (rRNA) is made

• Chromatin – DNA wound around protein units called histones– This form of DNA allows

efficient packing and storage of DNA (a nucleosome) during periods where the cell is not actively dividing

http://www.google.com/url?sa=i&rct=j&q=chromatin&source=images&cd=&cad=rja&docid=q6vAcG2dSRVOUM&tbnid=qz7qXycDDCVrRM:&ved=0CAUQjRw&url=http://faculty.jsd.claremont.edu/jarmstrong/researchint.htm&ei=OhcmUau3IorU9QSlpoGwDw&psig=AFQjCNHK0YII6yBdEtSatU1aADtymG6Szg&ust=1361537206835932

Nucleus - Chromosomes

• During cell division, chromatin winds up to form bar-shaped structures called chromosomes

• The arrangement of these structures allows the definition of different stages of cell division

Human Karyotype

• Chromosome sizes and number can also be used to screen for genetic diseases

http://www.google.com/url?sa=i&rct=j&q=trisomy+21&source=images&cd=&cad=rja&docid=bSMLI6S7Hc3edM&tbnid=3fgbbKhS4sGNBM:&ved=0CAUQjRw&url=http://www.allthingsdiscussed.com/More/Downs-syndrome-trisomy-21.php&ei=lhkmUdmuDpHi9gST44GYDw&psig=AFQjCNF23OejW0eKfEHFUwweCNeUzt1BIw&ust=1361537743946295

DNA Replication

Helicase

DNA Polymerase

DNA Polymerase

http://www.google.com/url?sa=i&rct=j&q=DNA+replication&source=images&cd=&cad=rja&docid=rShXX3i-7DRv_M&tbnid=vPUKw20k2h4ADM:&ved=0CAUQjRw&url=http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html&ei=taMsUfCHIIfe8wTAnIGIDQ&psig=AFQjCNHnK6m0AxPSa_kb7XqykYD4APF4TQ&ust=1361966329734864

http://www.google.com/url?sa=i&rct=j&q=DNA+replication&source=images&cd=&cad=rja&docid=vVZdA8YS2lL9FM&tbnid=GnHwbEiN_NpfSM:&ved=0CAUQjRw&url=http://serc.carleton.edu/microbelife/research_methods/genomics/replication.html&ei=l6ssUZ_PEY-w8AS4z4DQDw&psig=AFQjCNGSy4wtQuCRLQHrJ_SHy3TAcd712Q&ust=1361968402166179

RNA Transcription

• In order to make a protein, a “messenger” take the instructions from the DNA in the nucleus to the cytoplasm of the cell

• The act of copying a gene from DNA to RNA is called transcription

RNA

• RNA is a nucleic acid like DNA but with some important differences– The sugar (part of the backbone) is ribose, not

deoxyribose as it is in DNA– Nitrogenous bases are the same (adenine (A),

cytosine (C), guanine (G) and thymine (T)) except for thymine which is replaced by Uracil (U). • Uracil bonds to Adenine (U A)

Transcription Events

1. Initiation - RNA polymerase bonds to the gene to be transcribed (the promoter region)

2. Elongation - RNA polymerase unwinds the DNA strand and travels along the gene, adding RNA bases along the way to grow the mRNA strand

3. Termination - The RNA polymerase and new mRNA strand detaches and the DNA strand is closed.

Making mRNA (transcription)

Helpful Video!

• http://www.dnalc.org/resources/3d/12-transcription-basic.html

Translation – Making Proteins

• The mRNA (carrying the message made from the cell’s DNA) travels into the cytoplasm and attaches to a ribosome

• The ribosome “reads” the code on mRNA

Reading mRNA1. Transfer RNA (tRNA) molecules in the cytoplasm carry

amino acids and enter the ribosome

2. Each tRNA molecule has a series of 3 nitrogenous bases (the anti-codon region) that bind specifically to three bases in the mRNA strand

3. As mRNA and tRNA codons and anti-codons bond in the ribosome, the amino acids carried by the tRNA molecules bond and create a protein

4. A universal “stop” codon is read, which ends translation and releases the protein to be used by the cell

Protein Synthesis (Translation)

Another Helpful Video!

• http://www.youtube.com/watch?v=TfYf_rPWUdY&list=PLRSu0DZ2i6tGdGB8reN_yOyfkGq_AX2mE

The “CODE”

This code determines the type, number and order of amino acids that are deposited to make a protein

This is how all of the proteins are made in your body!