MCAT Anatomy CH 3,4

Description:	MCAT Anatomy CH 3,4 - Anatomy and Physiology (1)
Category:	MCAT
Created by:	analeah on 2007-09-16

Question	Answer
transcription	the synthesis of RNA using a DNA template (DNA -> RNA)
translation	synthesis of a polypeptide under the direction of mRNA (MRNA -> proteins)
Structure of RNA vs DNA	Rna - single stranded, ribose sugar, U replaces T & pairs with A DNA - Double stranded, deoxyribose sugar (mising O), ATGC, A&T, C&G
RNA Polymerase & 3 key features	catalyses the transcription of RNA from DNA Key Features - pries two DNA strands apart - synthesizes RNA in 5' -> 3' direction - doesn't need a primer to begin synthesis
RNA is always synthesized in what direction?	5' -> 3'
3 phases of transcription of RNA	1. Initiation 2. transcription elongation 3. Termination
Initiation phase of TRANSCRIPTION (3 steps)	1. transcription factors bind to promoter on DNA 2. RNA polymerase binds 3. RNA synthesis begins at the start point downstream from the TATA box
Transcription Elongation TRANSCRIPTION (4 key points)	1. Only one DNA strand is copied by RNA polymerase 2.RNA polymerase adds the complementary base pair on RNA 3. RNA polymerase moves in 5'->3' direction 4. Synthesizes RNA at rate of 60 nucleotides /sec
Transcription termination TRANSCRIPTION (3 key points)	1. termination sequence causes the RNA transcript to be released 2. In prokaryotes mRNA is immediately translated 3. in Eukaryotes, pre-mRNA transcript is modified before leaving nucleus (us)
Pre-mRNA Modifications after Transctipsions (where does it happen, what modifications)	Pre-mRNA mdifications in the nucleus before transportation into the cytoplasm. Modifications include: - 5' cap structure (capped with modified Guanine nucleotide) - 3' polyA tail (50=250 atenine nucleotides added
Why are pre-mRNA modifications made?	to facilitate transport of mRNA out of nucleus and to slow degradation of MRNA into cytoplasm
Other pre-mRNA modifications	introns removed from Pre-mRNA transcript Exons - covalently linked to form mature mRNA
Why have introns?	if one or more introns is not removed, a new mRNA transcript (and protein) can be synthesized
How could 4 nucleotides encode 20 amino acids?	4^3 = 64 (<20)
Codon	a three nucleotide sequence in mRNA that specifies which amino acid will be added to a growing polypeptide
Codon chart info (start codon, stop codon, how many codons code for each amino acid? )	- AUG = start codon & methionine - UAA, UAG, UGA = stop codon each amino acid has 4-6 codons
Functions and Structure of T-RNa	- carries an amino acid to the ribosome - binds a codon on mRNA -one head has an amino acid attachment site, oter has anticodon region which base pairs with MRNA
Ribosome	- coordinates the pairing of trna with mrna - composed of two subunits (Lg and sm
Each Ribosome has 3 sites	EPA - E - exit site P - (tRNA + growing polypeptide) A - (tRNA and the next amino acid to be added)
three stages of translation	initiation, elongation +translocation, termination
Initiation of Translation (3 steps)	1. small ribosomal subunit binds mRNA at the AUG 2. met-TRNA binds mRNa at the Aug site - the large ribosomal subunit binds NOTE: the met-RNA is in the P-site (middle)
Translational Ellongation + Translocation (4 steps)	1. tRNA binds to A site 2. Peptide bond formation between 2 amino acids 3. the tRNA in the A site moves to the P site - the tRNA in the P site moves to the E-site and is released
Translational Termination	Stop codons (do not code for an amino acid) - release factor binds to stop codon and breaks the bond between the tRna and the polypeptide
point mutation (def & 2 categories)	one base pair change in a gene Categories include: - base pair substitution - base pair insertions or deletions
Missense (point mutation)	point mutation resultin in a new amino acid in the protein
nonsense	point mutation resulting in the early stop in the amino acid sequence, - results in a truncated protein , always harmful effects
Base pair substitution & its results	the replacement of one base pair with another can result in: - little or no change in protein - less active or inactive protein (rare) - improved protein (very, very rare) sickle-cell
Insertions and deletions results	- more harmful than base pair substitutions because can have potential effet on reading frame can cause frameshift in mRNA