Cell structure and Function Physiology

Four basic types of biomolecules/macromolecules:

• Carbohydrates → sugars

• Lipids → fats

• Proteins (made of amino acids) → protein components

• Nucleotides → DNA, RNA

Functional groups

Contribute to molecules propensity to undergo specific chemical reactions

Intermolecular Forces

→ how molecules interact with one another in the universe

Carbohydrates are made up of

Composed of carbon, hydrogen, oxygen

Three types of Carbohydrates: Monosaccharides

simple sugar → most common is = glucose

Three types of Carbohydrates: Disaccharides

→ formed by covalent bond between two
monosaccharides

• Sucrose

Three types of Carbohydrates: Polysaccharides

→ many monosaccharides joined together

Can be broken down into glucose via hydrolysis?

Glycogen

→ stored form of glucose in human body

*Functions of carbohydrates

• Protects cell from mechanical damage → carbs in ECM = cushion

• Lubrication → carbs present in mucus

• Recognition → carbs on surface →unique cellular identity
  

• Adhesion → formation of glycoproteins = cell to cell interactions
  

• Energy source → primary source of energy
  

Lipids

mostly carbon and hydrogen

• Nonpolar(no dipole) covalent bonds (strong &sharing electrons)

• hydrophobic

5 classes of lipids

• Triglycerides

• Ketones

• Phospholipids

• Eicosanoids

• Steroids

Triglycerides

glycerol (3-carbon alcohol → backbone of Triglycerides)

+ 3 fatty acids (long carbon acid chain)

Fatty acid chains

• Nonpolar
  

• Hydrophobic → do not mix with polar molecules
  

• Saturated fatty acids → no double carbon bonds
  

• Unsaturated fatty acids → has double bonds
  

• Amphipathic → have polar and non-polar sections → Unique properties

Ketones

• Organic compounds with a carbonyl group (C=O) between two carbon

• Produced from fat breakdown

• Serve as alternative energy sources in ketosis

Ketosis

metabolic state in which body relies on fats as primary fuel source as opposed to carbohydrates

Hydrolysis of triglycerides in adipose tissue

Causes release of FFA’s(Free Fatty Acids) into blood

FFA’s(Free Fatty Acids) are converted to…

ketone bodies in the liver

Acetoacetic acid

energy source during fasting

RBC’s (red blood cells) cannot use ketones

(require glucose)

Phospholipids

amphipathic molecules

• Polar head + non-polar tail – amphipathic molecules

• Contains two tails → attached phosphate group

Formation of phospholipid bilayer

• Critical in establishment of electrochemical gradient

• Needed to make ATP

• ATP = molecular currency of biology

Eicosanoids

• Modified fatty acids

• Intracellular communication

• Prostaglandins, thromboxane

types of eicosanoids: Prostaglandins

Potent

• Act in low concentrations on local targets

• Initiate a large array of downstream effects
  Inflammation, pain, vasodilation
  

types of eicosanoids:Thromboxane

• Synthesized from platelets
  

• Involved in platelet aggregation (blood clotting)

Steroids

All steroids are derived from cholesterol

• Contain four rings

Cholesterol

Important in cell membrane fluidity

• Cholesterol = precursor molecule of bile salts

Bile salts

are formed in liver

• Help digestion of fats

Ex. of steroids

• Estrogen

• Testosterone

• Aldosterone

Amino acids

u Building blocks of proteins

u Twenty different kinds of amino acids

u Amino acids are linked together by peptide bonds

Polymers

(chains)/multiple of amino acids

Peptides

Generally 2-50 amino acids

Proteins

more than 50 amnio acids

• have many functions

Levels of protein structure: Primary structure

Sequence of AAs(amino acids) connected via peptide bonds

Levels of protein structure: Secondary structure

α-Helixes

β-Pleated sheets

Levels of protein structure: Tertiary Structure

Formation of bends and loops in a polypeptide chain

• hydrogen bonds

• Ionic bonds (strong)

• Van der Waals forces

• Covalent bonds (sttong)

• Cystine R group → formation of disulfide bridge

Levels of protein structure: Quaternary structure

Only exists when there is more than one polypeptide interacting

• Ex)  hemoglobin

Image of Levels of protein structure

Nucleotide structure

Phosphate group

Five-carbon carbohydrate

• Ribose

• Deoxyribose

Nitrogenous bases

• Pyrimidines (cytosine, thymine, uracil)

• Purines (adenine, guanine)

Nucleic acids

polymers of nucleotides

DNA

stores genetic code

• double stranded

• Helix

RNA

Needed for expression of genetic code

• usually single stranded

DNA→ RNA→ Protein

Bases: Purines

Adenine (A)

Guanine (G)

Bases: Pyrimidines

Cytosine (C)

Thymine (T)

DNA carbohydrate

deoxyribose

Law of complementary base pairing

• A-T (A-U)

• C-G

For RNA Uracil instead of thymine (A-U)

RNA carbohydrate

ribose

Different functions of the cell: Movement

muscle cells → sliding filament theory

Different functions of the cell: Conductivity

nerve cells → depolarization

Different functions of the cell: Metabolic absorption

cells taking in nutrients → glucose

Different functions of the cell: Secretion

glands secreting mucus → hay fever

Different functions of the cell: Excretion

elimination of waste materials 

Different functions of the cell: Respiration

biological fuel oxidized to make energy → ATP

Different functions of the cell: Reproduction

tissue growth, cells enlarge and reproduce themselves

Different functions of the cell: Communication

cells communicate to one another → chemical signaling

Nucleus

Largest membrane-bound organelle

• Cell division → site of mitosis

• Controls genetic Information

Cytoskeleton

→ give cells support

Cytoskeleton component: Microfilament

(made up of actin molecules) → smallest

• Strands of actin, inter-twined

• Actin are involved in → muscle contraction and cell division

Cytoskeleton component: Intermediate filaments

maintain cells structure (anchoring)

• Stronger than microfilaments → structural proteins → keratin

Help anchor neighboring cells together, and anchor organelles within cell

Cytoskeleton component: Microtubules

largest

• Made up of proteins → alpha and beta tubulin proteins

Involved intracellular movement movement, cell division

Cytoplasm

is an aqueous solution (cytosol)

• fluid that fills all the space between all the organelles

Organelles → suspended in cytoplasm  → enclosed in biologic membranes 

Ribosomes

uRNA protein complexes → found of rough ER

uSite for protein synthesis

umRNA undergoes modifications → 5' cap = necessary for initiation of translation

uPoly-A tail → prevents mRNA degradation

Endoplasmic Reticulum (ER)

Network of tubular channels (cisternae)

Smooth ER

synthesis of phospholipids, fatty acids, cholesterol, and steroids

• Detoxification of drugs

Rough ER

synthesis of membrane, secretory, and lysosomal proteins

Makes proteins

• Packages newly synthesized proteins into vesicles → transport to golgi for processing

Golgi complex

• Network of smooth membranes

Processing and packaging of proteins

• Proteins  get transported throughout cell

Site of post-translational modification

• High traffic area of the cell

Lysosomes

recycling center of cells

• Saclike structures

Contains degradative enzymes (acidic hydrolases) –active in acidic env.

• Digest cellular substances into basic forms

Respond to cellular injury → enzyme release → leads to cellular self-destruction 

Peroxisomes

Protective roll in cell

• Break substances down into harmless products

Similar  to lysosomes

• Detoxify waste products

Contain oxidative enzymes 

• Protects cells from hydrogen peroxide → breaks it down

Contains enzyme catalyze

Mitochondria 1

Cellular energy metabolism

ATP generation!

Occurs within inner membrane of mitochondria 

Powerhouse of cell

Osmotic regulation

• Modulates movement of water and ions

Mitochondria 2

pH control

• Buffering capacity → H+ gradient

• Contains various buffering molecules (bicarbonate)

Calcium homeostasis

• Calcium transport systems → VDCAS (voltage-gated calcium channels)

  Regulate intracellular calcium levels

Plasma Membrane Functions

Cell-to-cell recognition → receptors on cell surface

Cellular mobility → fluid mosaic model

Cellular shape → cytoskeletal components

Movement of molecules → protein channels 

Plasma Membrane Composition

Basic structure of plasma membrane = lipid bilayer

Various proteins + carbohydrates

Bound to membrane proteins (glycoproteins) and lipids (glycolipids)

Protein regulation (proteostasis)

Main role is minimize protein misfolding and protein aggregation

Protein regulation (proteostasis) Regulated by:

Ribosomes (makers)

Chaperones (helpers)

Proteolytic systems  → set of enzymes and mechanisms involved in protein breakdown

Lysosomes

• Ubiquitin-proteasome system (UPS) 

• Helps regulate protein homeostasis

Proteostasis malfunction

associated with human disease

Kuru

Mad disease

Tight Junctions

intracellular adhesion complexes

Connects to adjacent cells together

Limit movement of molecules between intracellular spaces (paracellular movement)

Found in epithelium

Occludins

proteins which link cells together

Integral proteins = permanently attached to membrane

Formation tight junctions

Force special type of transport → transepithelial transport

Transepithelial transport

• Direct movement through the cells, rather than between them (paracellular movement)

Desmosome

filamentous junction between cell

• Binds cells together for strength

Found in tissue subject to mechanical stress

• Enable stretching

Cadherins → proteins within desmosomes

• Help make connections within desmosome

Gap Junctions

Channel protein

Permits electrical and chemical communication between cells

Enables ions to move between two adjacent cells

Intracellular signaling

Cells are connected via → connexon → made of connexins = proteins

Gene

Portion of DNA holding genetic code → codes for a proteins

Codons

Genes are read in triplets = Codons

code for specific amino acids

Initiator codon (AUG)

found in every mRNA

AUG

Codes for methionine

Enable translation to start

Termination codons

(stop codons)

UGA, UAA, UAG

Translation stops

The Genetic code

DNA

• Transcribed into mRNA

mRNA translated into protein

A triplet is transcribed into a codon

Code for 20 amino acids

Transcription

DNA is transcribed into mRNA

Primarily Three types of RNA are transcribed:

mRNA: Messenger

rRNA: Ribosomal

tRNA: Transfer

Promotor sequence (Transcription)

DNA sequence before the gene

Initiates transcription of gene

RNA polymerase binds promoter sequence

Initiation of transcription

RNA polymerase catalyzes bonds between nucleotides

mRNA strand is synthesized

Transcription

mRNA Processing: Introns

Non-coding regions of mRNA

Excised out of mRNA

mRNA Processing: Exons

Coding sequences

Spliced together

add 5' CAP → necessary for initiation of translation

add 3' poly A tail → protects mRNA from degradation

Mature mRNA

Transported outside of nucleus

Translation in cytosol

Translation

Process of synthesizing proteins

Occurs in cytoplasm

DNA → RNA → Protein

mRNA → carrying code from DNA template

tRNA → transfer RNA → brings amino acid to ribosome during translation

rRNA → ribosomal RNA → makes up ribosome needed for translation

Transcription →

Translation →

Replication →

Transcription → making mRNA from DNA

Translation → making protein from mRNA

Replication → making copies of DNA

Replication

copying DNA

Chromosome

one complete DNA molecule plus associated proteins

Humans have 23 pairs of chromosomes

• One paternal, one maternal

• All 23 chromosome pairs make up the human genome

Chromosomes are coiled around histones = proteins

DNA = net

(-) charge