part 1 for unit 2 of cell molecular bio
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What is one property shared by all proteins?
A: They bind other molecules.
What determines what a protein can bind?
A: Its three-dimensional shape and chemical properties.
What is one property shared by all proteins?
A: They bind other molecules.
Why are disulfide bonds important?
A: They stabilize protein structure.
Why are disulfide bonds especially common in extracellular proteins?
A: Extracellular proteins require extra stabilization outside the cell.
Where are disulfide bonds commonly formed?
A: In the endoplasmic reticulum.
What are disulfide bonds?
A: Covalent bonds formed between two cysteine residues.
Which protein provides elasticity and flexibility?
A: Elastin.
Which protein provides strength and resists stretching?
A: Collagen.
What is the main function of elastin?
A: Allows tissues to stretch and recoil.
What is the main function of collagen?
A: Provides tensile strength to tissues.
What are fibrous proteins?
A: Long structural proteins that provide support and strength.
What are viral capsids primarily made of?
A: Repeating protein subunits that form a protective shell.
What is an actin filament?
A: A filament composed of repeating actin protein subunits.
What structures can proteins assemble into?
A: Filaments, rings, tubes, sheets, and spherical shells.
What is a dimer?
A: A protein made of two associated subunits.
What is a protein subunit?
A: A single polypeptide chain that is part of a larger protein complex.
Why are proteins grouped into families?
A: Similar amino acid sequences often produce similar structures and functions.
What is a protein family?
A: A group of proteins that share similar sequences, structures, and functions.
Why are protein domains important?
A: Different domains often perform different functions.
What is a protein domain?
A: A region of a protein that folds independently into a stable structure.
What does secondary structure describe?
A: Local folding patterns such as α-helices and β-sheets.
What does tertiary structure describe?
A: The overall three-dimensional shape of one polypeptide.
What does quaternary structure describe?
A: The arrangement of multiple polypeptide chains into one functional protein.
Do all proteins have quaternary structure?
A: No, only proteins made of multiple polypeptide chains.
What interactions usually stabilize quaternary structure?
A: Noncovalent interactions between subunits.
In a parallel β-sheet, how do neighboring strands run?
A: In the same direction.
What does primary structure describe?
A: The amino acid sequence.
In an antiparallel β-sheet, how do neighboring strands run?
A: In opposite directions.
What are the two types of β-sheets?
A: Parallel and antiparallel.
What is a major function of β-sheets?
A: They provide rigidity and strength to proteins.
What are β-sheets?
A: Sheet-like protein structures formed from hydrogen-bonded polypeptide strands.
Name two important coiled-coil proteins.
A: α-Keratin and Myosin.
What interaction primarily holds coiled-coil proteins together?
A: Hydrophobic interactions.
What are coiled-coil proteins?
A: Rodlike proteins formed when multiple α-helices wrap around one another.
What stabilizes an α-helix?
A: Hydrogen bonds between backbone N-H groups and C=O groups.
What is the main function of ribosomes?
: Ribosomes synthesize proteins by translating mRNA into a polypeptide chain.
What are ribosomes made of?
: Ribosomal RNA (rRNA) and ribosomal proteins.
Why are ribosomes considered ribozymes?
Because the rRNA catalyzes peptide bond formation.
Where can ribosomes be found in eukaryotic cells?
Attached to the rough ER or free in the cytosol.
What is a polysome (polyribosome)?
Multiple ribosomes translating the same mRNA simultaneously.
What is the advantage of polysomes?
A: Many copies of a protein can be produced from one mRNA at the same time.
Are polysomes found in prokaryotes, eukaryotes, or both?
both
Why can transcription and translation occur simultaneously in prokaryotes?
A: They lack a nucleus.
Why are transcription and translation separated in eukaryotes?
The nucleus separates transcription from translation.
In the prokaryotic "Christmas tree" structure, what does the trunk represent?
DNA.
In the prokaryotic "Christmas tree" structure, what do the branches represent?
A: mRNA molecules being transcribed.
In the prokaryotic "Christmas tree" structure, what do the beads represent?
ribosomes
Where does transcription occur in eukaryotic cells?
nucleus
where does translation occur in eukaryotic cells
cytoplasm or rough er
what are introns
non-coding regions removed from pre-mRNA
what are exons?
coding regions that remain in mature mRNA
what is RNA splicing
removal of introns and joining of exons
what are the 2 ribosomal subunits?
large subunit and small subunit
what is the function of the small ribosomal subunit
decodes mRNA and recognizes codons
what is the function of the small ribosomal subunit
decodes mRNA and recognizes codons
what is the function of the small ribosomal subunit
Decodes mRNA and recognizses codons
what is the function of the large ribsosmal subunit
decodes mRNA and recognizes codons
what does the S in 70S and 80S stand for
sedimentation rate in svedberg units
ribosome size in prokaryotes
70S
subunits that make up prokaryotic 70S
50S large subunit and 30S small subunit
what is the ribosome size of eukaryotes
80S
subunits which make up eukaryotic 80S ribosome
60S large subunit and 40S small subunit
3 stages of protein synthesis
initiation, elongation, termination
what codon starts translation
AUG
which amino acids corresponds to the start codon AUG
methionine
what happens during initiation
ribosome binds to mRNA, finds AUG and initiator tRNA binds
what happens during elongation
amino acids are added to growing polypeptide chain
what happens during termination
a stop codon is reached, protein is released and the ribosome dissociates
what are the 3 stop codons?
UAA, UAG, UGA
which ribosomal site holds the growing polypeptide chain
P site (peptidyl site)
which ribosomal site releases empty tRNA
E-site (exit site)
order of ribosomal sites
APE = arrive, peptide, exit
what is post-translational import
protein is completely synthesized before entering an organelle
what is co-translational import
protein eneters and orgnalle while its being synthesized
what are proteins made from
amino acids linked by peptide bonds
how mnay standard amino acids make a protein
20
what determines a proteins shape
amino acid sequence
what type of interactions primarily stabilize protein folding
noncovalent interactions
what 3 non-covalent interactions stabilize proteins
hydrogen bonds, electrostatic interactions and van der waals interactions
where are nonpolar amino acid side chains usually found
inside hydorphobic core
where are polar amino acid side chains usually found
on outside of the protein interacting with water
what structure are formed by backbone-backbone hydrogen bonds
α-helices and β-sheets.
what is the function of backbone-side chain hydrogen bonds
hold distant parts of the protein tg
proteins fold into what type of conformation
the lowest energy conformation
is protein conformation determined soley by its amino acid sequence
yes
which process occurs on ribosomes? transcription of translation
translation
which process occurs in nucleus
transcription
what is the flow of protein synthesis
start - grow - stop
most important function of large ribosomal subunit
catalyzes peptide bond formation
most important function of the small ribosomal subunit
decodes mRNA codons