Exam 3 Flashcards
translation
information in an mRNA is translated into a protein
necessary components for translation
- mRNA with genetic code
- ribosomes
- transfer RNAs (tRNAS)
genetic code
series of codons on an MRNA
* codon: sequence of 3 nucleotides
codon function
- specifiy a particular amino acid
- signal where translation should start or step on mRNA
- necessary b/c mRNA have 5β and 3β untranslation regions which are not supposed to be translated
characteristics of genetic code
- 64 codons
- universal
- redundant
- 64 codons and 20 AA
- 1 start and 1 stop codon
ribosomes
enzyme complexes that translate the info in mRNAS into proteins
* made of 2 subunits
1. large ribosomal subunit
2. small ribosomal subunit
* each subunit is made of multiple ribosomal proteins and RNAs
ribosome function
- small subunit - positions mRNA
- large subunit - peptide bond formation, * recognition of stop codon and protein release
- both bind tRNA
- enzymatic function - catalyze rxns (ribozymes)
tRNA function
carry the amino acids to ribosome to be incorporated into a protein
uncharged tRNA vs charged tRNA
uncharged: no AA
charged: AA
3 Phases of Translation
- initiation: assembly of mRNA, ribosome, and initiator tRNA
- elongation: starts at start codon (met) and AAS are added until stop codon
- termination: new protein is released from ribosome, ribosome disassembles
Prokaryotic Initiation Steps
- mRNA has a 5β ribosome binding sequence - complementary to rRNA in small ribosomal subunit
- initiator tRNA binds to start codon (AUG)
large ribosomal subunit joins and initiation is complete
Eukaryotic Initiation steps
- Small ribosomal subunit + initiator tRNA binds to the mRNA 5β cap
- Complex scans mRNA until it finds the start codon
- Large ribosomal subunit joins the complex and initiation is complete
Ribosome tRNA Binding Sites
P site: where initiator tRNA binds
A site: where the next tRNA binds, carrying the next AA to be added to the protein
E site: where uncharged tRNAs are ejected
translocation
movement of the ribosome down the length of the mRNA
Translation Termination
- No tRNAS binds to the stop codon
- Release factor (a protein) binds to the stop codon
- Synthesized protein is released from the ribosome
- Ribosome complex falls apart
Primary structure
sequence of AA in a protein
secondary structure
folding of protein caused by interactions within peptide backbone
* h-bonding
* ex. alpha-helix, beta pleated sheets
super secondary structure
forms when πΌ-helices and π½-pleated sheets combine in various ways to form motifs
Tertiary Structure
the highest level of structure for a single protein
Stabilized by interactions between the R-groups of the amino acids
stabilizing tertiary structures
- Electrostatic interactions: H-bonds and ionic bonds between R-groups
- Disulfide bridges: cysteine has a sulfhydryl (SH) group
- SH groups of cysteine can form covalent bonds called disulfide (S-S) bridges
- Disulfide bridges: cysteine has a sulfhydryl (SH) group
- SH groups of cysteine can form covalent bonds called disulfide (S-S) bridges
- Hydrophobic interactions
domain
subunit on a protein with a specific function
DNA binding domain (DMD)
any protein that directly binds to DNA needs a DNA binding domain
transcriptional activation domain (TAD)
Activating transcription of a gene requires a transcriptional activation domain (TAD) to attract/interact w/ RNA polymerase
Quaternary Structure
interaction of 2 or more proteins to form a multi-protein complex
Chaperone proteins:
enzymes that help proteins fold/refold into the proper shape
Epigenetic Modifications
modifications that change the expression of genes w/ out changing the DNA sequence of the gene
Often change the chromatin structure of a gene
What do epigenetic modifications change
how tightly DNA and histones bind to each other
Euchromatin
DNA & histones are loosely associated and DNA very accessible to transcription factors/RNA pol. binding
Heterochromatin
DNA & histones are tightly associated and DNA is not very accessible to transcription factors/RNA pol.
Methyl group
physical barrier to binding of transcription factors (inhibits gene transcription)
Hydrophobic Ligands
- Can diffuse across the plasma membrane
- Bind to intracellular receptors (IRs) in the cytoplasm
- IRs have an intracellular ligand binding domain which causes the IR to transduce a signal into the cell
Hydrophilic Ligands
- Polar and canβt diffuse across the plasma membrane
- Hydrophilic ligands must bind to membrane-bound receptors which have 3 protein domains
1. Extracellular ligand binding domain
2. Transmembrane domain (goes through the plasma membrane)
3. Intracellular signaling domain (transduces the signal)
Agonists
mimic the action of ligands that would normally bind to the receptor (activate receptors)
Antagonists
bind to but do NOT activate receptors
Blocks other ligands from binding to receptor
Embryonic development
gene-directed changes that occur after fertilization that lead to the formation of an organism
Homeotic genes
genes critical for making sure anatomical structures develop in the correct location and correct number
Morphogens
diffusible ligands (signaling molecules) that affect cell fate during development
* gradients
Central nervous system (CNS
consists of brain, spinal cord, and interneurons within the brain and spinal chord
Peripheral nervous system (PNS)
consists of sensory neurons and motor neurons
sensory neurons
carry info about body & environment to CNS
interneurouns
provide a link between the sensory neurons, brain, and motor neurons
Motor neurons (PNS):=
carry impulse from CNS to effectors (muscles, glands)
Dendrites
receive signals (using receptors) and send electrical pulses (action potentials) to the cell body
Axon:
conducts the action potential to the axon terminals (ends)
cell body
has nucleus and other metabolic machinery, can decide whether or not to transmit action potential to axon
Axon terminals:
transmit the signal through a synapse to the next cell
