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Bio Lecture-Sec
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1: Nucleic Acids II

⁃ Proteins come in all shapes & sizes, & are specialized for specific functions w/ in a cell
⁃ instructions to make proteins are encoded in DNA, & must be “accessed” for proteins to
be made
⁃ a cell builds the proteins it needs from instructions encoded in its DNA according to the
central dogma of molecular bio
⁃ Transcription:
⁃ introns must be removed from eukaryotic RNA transcripts before translation can
occur
⁃ the transcription of eukaryotic genes by RNA polymerase generates a primary
RNA transcript that contains axons & introns
⁃ introns are removed by process called splicing
⁃ primary RNA transcripts are also processed by the addition of a 5’ cap & a poly
(A) tail
⁃ w/ addition of cap & tail & completion of splicing, mature mRNA is made

Bio Lecture- Sec
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2:

⁃ Amino acid structure: 2 forms
⁃ non-ionized form of amino acid
⁃ ionized form of amino acid
⁃ The 20 amino acids differ only in the unique R-group attached to the central carbon
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types of proteins active in them
⁃ Protein Folding & Function:
⁃ for protein to become active it must change it’s functional structure/shape

 changing shape is how proteins are regulated (change in shape causes it to go
from inactive to active)
What proteins do:
⁃ act as catalysis: enzymes speed up chemical reactions
⁃ defense: antibodies and complement proteins attack pathogens
⁃ movement: motor & contractile proteins move the cell or molecules w/in cell
⁃ signaling: proteins convey signals b/t cells
⁃ structure: structural proteins define cell shape & compromise body structures
⁃ transport: carry materials
Protein Misfolding & Disease: folding inappropriately
⁃ Prion Protein: exist in normal form & infectious form
⁃ when infectious proteins interacts w/ normal one it causes the normal protein to
refold & become infectious as well
Transcription & Translation:
⁃ DNA is transcribed to messenger RNA by RNA polymerase
⁃ transcription: the process where the hereditary info in DNA is copied to RNA
⁃ the mRNA is then translated to protein
⁃ translation: the process wherein the language of nucleic……

creates the primary structure of a protein
⁃ The Genetic Code: there are 4 RNA bases (U, C, A, G)
every 3 nucleotides in 1 RNA encodes for an amino acid
⁃ AUG encodes for the amino acid Methionine (Met)
⁃ Methionine is the start codon (every gene starts w/ Met)
Important Properties of Code:
⁃ it’s redundant: all amino acids except two are encoded by more than one codon
⁃ it’s unambiguous: one codon never codes for more than one amino acid
⁃ it’s nearly universal: all codons specify the same amino acids in all organisms
Reading Frame: amino acid encoded depends on which nucleotide of a codon is read
first (b/c triplicate codon)
⁃ the way it’s read will result in different amino acid sequences meaning different
proteins
In translation the sequence of bases in mRNA is converted to an amino acid sequence in
a protein
ribosomes catalyze translation of mRNA sequence into protein
tRNA fold on themselves to make a complex secondary structure
anticodon: complement of the triplet in the mRNA that allow it to match
tRNA bonds to mRNA & peptide bond forms
allows tRNA to attach to ribosome
ribosomes contain protein & ribosomal RNA (rRNA)
⁃ these can be separated into 2 subunits (large & small subunits)
Phases of Translation:
⁃ initiation, elongation, & termination
⁃ Initiation:
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translation begins by small ribosomal unit sliding along until it finds the AUG start codon
⁃ Elongation: has 3 steps
arrival of tRNA
Peptide bond formation
translocation (the whole ribosome shifts down one codon of space)
⁃ Termination:
release factor (special proteins) binds to stop codon: this interaction causes the subunits
to fall apart
polypeptide & uncharged tRNAs released
ribosome subunits separate (translation STOPS)
⁃ Post-Translational Modifications:




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