cell biology 1 Flashcards
enzymes
function as catalysts, increasing the rates og chemical reactions
structural proteins
physical support and shape
motility proteins
contraction and movement
regulatory proteins
control and coordinate cell function
transport proteins
move substances in and out of cells
hormonal proteins
communication between cells
defensive proteins
protect against disease
storage proteins
reservoirs of amino acids
receptor proteins
enable cells to respond to chemical stimuli from the environment
how many amino acids used in protein synthesis?
20
which stereoisomer occur in proteins?
L-amino acid
dehydration / condensation reactions
Amino acids are linked together stepwise into a linear polymer by DEHYDRATION (or CONDENSATION) reactions
the end of polypeptide with the amino group
is called N (or amino) terminus
the end of the polypeptide with the carboxyl group
is called C (or carboxyl) terminus
protein synthesis
The process of elongating a chain of amino acids
conformation
protein proper shape
both covalent bonds and noncovalent interactions are needed for a protein to
adopt its proper shape
bonds in protein
disulfide bond
hydrogen bond
ionic bond
Van der Waals and hydrophobic interactions
covalent disulfide bonds
They form through the removal of two hydrogen ions (oxidation) and can only be broken by the addition of two hydrogens (reduction)
intramolecular disulfide bonds
form between cysteines in the same polypeptide
intermolecular disulfide bonds
form between cysteines in two different polypeptides
noncovalent bonds and interactions
hydrogen and ionic bonds, and van der Waals, and hydrophobic interactions
these are individually weaker than covalent bonds but collectively can strongly influence protein structure and stability
donors
hydroxyl groups of several amino acids
acceptors
carbonyl or sulfhydryl groups
ionic bonds
electrostatic interactions
form between positively and negatively charged R groups
Because they depend on the charge on the R groups, changes in pH can disrupt ionic bonds
four levels of organization in the protein
primary structure - amino acid sequence
secondary structure - local folding of polypeptide
tertiary structure - three-dimensional confirmation
quaternary structure - interactions between monomeric proteins to form a multimeric unit
primary structure
amino acid sequences are written from the N-terminus to the C-terminus
primary structure is important genetically because the sequence is specified by the order of nucleotides in the corresponding messenger RNA
secondary structure
describes local regions of structure that result from hydrogen bonding between NH and CO groups along the polypeptide backbone
These result in two major patterns, the alfa helix and the beta sheet
alfa helix
spiral shape
A hydrogen bond forms between the NH group of one amino acid and the CO group of a second amino acid that is one turn away from the first
beta sheet
extended sheetlike conformation with successive atoms of the polypeptide chain located at “peaks” or “troughs”
motifs
Examples include the beta-alfa-beta, the hairpin loop (beta-beta), and the helix-turn-helix motifs (alfa-alfa)
tertiary structure
The tertiary structure reflects the unique aspect of the amino acid sequence because it depends on interactions of the R groups
native conformation
The most stable possible three-dimensional structure of a particular polypeptide
proteins can be divided into two broad categories
fibrous proteins
globular proteins
fibrous proteins
have extensive regions of secondary structure, giving them a highly ordered, repetitive structure
glovular proteins
folded into compact structures
domain
is a discrete locally folded unit of tertiary
structure, usually with a specific function
quaternary structure
the bonds and forces maintaining quaternary structure are the same as those responsible for tertiary structure
sometimes molecular chaperones are required to assist the process
nucleic acids
store, transmit, express genetic information
DNA
deoxyribonucleic acid
RNA
ribonucleic acid
RNA synthesis
transcription
mRNA export
translation (takes place in cytoplasm)
purines
adenine
guanine
pyrimidines
thymine
uracil
cytosine
in nucleic acids nucleotides are linked by
3’,5’ phosphodiester bridge
nucleotide sequences are conventionally written in the
5’ to 3’ direction
complementary base pairing
A - - T
G - - - C
polysaccharides
long chain polymers of sugars and sugar derivatives that are not informational molecules
aldosugars
terminal carbonyl group
ketosugars
internal carbonyl group
glucose
aldohexose D-glucose (C6H12O6)
DDDDDDDDD most stable form of glucose
alfa D glucose
hydroxyl group downward
beta D glucose
hydroxyl group upward
storage polysaccharides
starch - plant cells
glycogen - animal cells
Both consist of -D-glucose units linked by - glycosidic bonds, involving carbons 1 and 4 (1→4)
cellulose
composed of repeating monomers of beta-D-glucose
lipids
hydrophobic nature
functions include energy storage, membrane structure, or specific biological functions such as signal transmission
fatty acids
the polar carboxyl group is the “head” and the nonpolar hydrocarbon chain is the “tail”
saturated fatty acids
no double bonds, pack together well
solid at room temperature
unsaturated fatty acids
one or more double bonds, so have bends in the chains and less tight packing
liquid at room temperature
phosphoglycerides
are the predominant phospholipids in most membranes
sphingolipids
are basedon the amine sphingosine, which has a long hydrocarbon chain with a single site of unsaturation near the polar end
