cell bio chapter 4

protein structure and function

Structural protein

Provides the cell with shape and structure (Actin, Lamin
A/C, tubulin)

Also help with movement

Enzymes

Catalyze covalent bond breakage or formation (Trypsin,
polymerases)

Create and break bonds

Polymerase

hand shaped enzyme

Transport protein

Carries other molecules or ions (Hemoglobin)

Motor protein

Generates movement in cells and tissues (Myosin)

Storage protein

Stores small molecules or ions (Ferritin)

Signal protein

Carries signals from cell to cell or within the cell (Insulin)

Receptor protein

Detects signals and transmits them to the cell’s response
machinery (Insulin receptor)

Gene regulatory protein

Binds to DNA to switch genes on or off (p53, p21,
lactose repressor)

Makes sure we can have different kinds of cells

R groups

Differentiate the 20 different amino acids from each other

peptide bonds

Protein covalent bonds that are responsible for linking amino acids together

Polypeptide

synonym for protein

Carboxyl groups

make up the backbone of the polypeptide chain

N-terminus

End with amino group

C-terminus

End with carboxyl group

polypeptide chain

amino acids that are linked together and make up a protein

20

Number of different amino acids commonly found in proteins

Noncovalent bonds

help proteins fold

Hydrogen bond

Interaction between a positively charged hydrogen atom in one molecule and a
negatively charged atom in another

help stabilize a molecule’s folded shape

electrostatic attractions

also known as ionic bonds

van der Waals attractions

Weak interaction due to fluctuating electrical charges and often hydrophobic

Hydrophobic interactions

Minimize the distribution of hydrophobic molecules within water

hydrophobic forces

help proteins fold into compact formations

Denatured proteins

AKA misfolded proteins that can sometimes recover their natural shapes to
maintain a conformation of lowest energy

Integral proteins

Within the membrane

Ex. alpha helix, helical bundle, beta barrel

Prion diseases

caused by rare proteins
whose misfolding is infectious

Chaperone proteins

can guide the folding of newly synthesized polypeptide chains

can also act as isolations chambers that help a polypeptide fold

functional domains

areas of a polypeptide chain that are shaped for different functions

dimer

two chains that come together

tetramer

four chains that come together

cofactor

protein that needs a non-protein entity to function

ex. hemoglobin

primary level

Amino Acid
Sequence

Secondary level

α-helices and
β-sheets

Tertiary level

Folding involving side chains (R groups)

Quarternary level

Multiple polypeptide chains come together to form a complex

Alpha helix

Segments can cross a lipid bilayer and intertwine to form a stiff coil

Beta pleated sheet

strands held together by hydrogen bonding between peptide bonds

Can stack to form an amyloid structure

Beta pleated sheet varieties

Parallel and antiparallel

Actin filament

composed of identical protein subunits

Single protein subunits

can pack to form a filament, tube, or a spherical shell

Collagen

is a triple helix formed by three
protein chains that wrap around one another

Disulfide bonds

covalent bonds that help stabilize a favored protein conformation by making a disulfide bridge

Scaffold proteins

can concentrate interacting proteins in the cell

Cavity

created by the folding of a polypeptide chain

Binding sites

allow a protein to interact with specific ligands

Antibody

Y-shaped and has two identical
binding sites for its antigen

Catalysis

promoted by enzymes

Feedback inhibition

regulates a flow through biosynthetic pathways and triggers a
conformational change

Increased ligand (ADP concentration)

activates the enzymatic reaction for oxidation of sugars

Protein phosphorylation

a very common means of regulating protein activity

Motor protein

driven by ATP hydrolysis and moves in one direction