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From Gene to Protein: Key Terms/Concepts
- Gene Expression
- Transcription: events from DNA to RNA
- After transcription: How RNA is modified
- Steps to translation
- Translation: RNA to protein
- Central Dogma (DNA - RNA - protein)
- Point mutations change amino acid sequence of protein
- Nucleic acid composed of nucleotides
- Double stranded
- Deoxyribose: one less sugar
- Template for individual
- Nucleic acid composed of nucleotides
- Ribose = sugar
precursor to mRNA, newly transcribed and not edited
Edited version, carries code from DNA that specifies amino acids
Carries amino acid to ribosome based on its anticodon to mRNA codon
Makes up 60% of ribosome, site of protein synthesis
srpRNA (signal recognition particle)
Binds to signal peptides, cuts off pre-mRNA.
Codons (mRNA triplets): code for amino acids in polypeptide chain
Living things are made of 20 amino acids
64 different codon combinations
Redundancy: 1+ codons code for each of the 20 amino acids
Reading frame: groups of 3 must be read in correct groupings
Sets up 3 bases that code for same amino acid
Transcription (DNA - RNA)
Unit: stretch of DNA that codes for a polypeptide or RNA (tRNA, rRNA)
RNA Polymerase II: Separates DNA strands and transcribes mRNA. Attaches to promoter (start of gene), stops at terminator (end).
mRNA elongates in 5' - 3'
Uracil replaces thymine when pairing to adenine
TATA box: DNA sequence (TATAAAA) upstream from promoter.
Transcription factors recognize TATA box before RNA polymerase can bind to DNA promoter.
RNA polymerase adds RNA nucleotides to the 3' end of growing chain (A-U, G-C)
Polymerase untwists DNA, then rewinds it after mRNA is made.
RNA polymerase transcribes a terminator sequence in DNA, then mRNA and polymerase detach
Now called pre-mRNA.
Eukaryotic cells modify RNA
5' cap is added (modified guanine)
3' poly-A tail (50-520 A's) are added
These help export from nucleus, protect enzyme degradation, and attach to ribosomes
pre-mRNA has introns (noncoding sequences) and exons (codons for amino acids)
Introns are cut out, exons are expressed and stay, join together
Small nuclear ribonucleoproteins = snRNPS
- Recognize splice sites
- Join with proteins to form spliceosomes, which start process of removing introns and joining exons
- Makes pre-mRNA into mRNA
Introns regulate gene activity, produce different combinations of exons
- 20,000 genes = 100,000 polypeptides
Translation: RNA directed synthesis of polypeptide
Components: mRNA (message), tRNA (interpreter), ribosome (site)
tRNA is transcribed in the nucleus and is specific to each amino acid. It transfers AA to ribosomes.
- Anticodons pair with codons.
- Base pairing rules between 3rd base of codon are not as strict = wobble
Ribosomes are made of rRNA and proteins. Made in nucleus with 2 subunits.
- A site: holds AA to be added
- P site: holds growing polypeptide chain.
- E site: exit for tRNA
Small subunit binds to start codon (AUG) on mRNA.
tRNA carrying MET (AA) attaches to P site.
Large subunit attaches.
Codon recognition: tRNA anticodon matches codon in A site.
Peptide bond formation: AA in A site forms bond with peptide in P site.
Translocation: tRNA in A site moves to P site, tRNA in P site moves to E site and exits.
Stop codon reached and translation stops.
Release factor binds to stop codon, polypeptide released.
Ribosomal subunits dissociate.
Single mRNA can be translated by several ribosomes at the same time.
During synthesis, polypeptide chain coils and folds spontaneously. Chaperonin protein helps polypeptide fold correctly.
Types of ribosomes
Free: synthesize proteins that stay in cytosol.
Bound (to ER): Make proteins of endomembrane system (nuclear envelope, ER, golgi, lysosomes, vacuoles, membrane), and proteins for secretion
- Uses signal peptide to target location.
Point mutations: Basics
Happen in DNA and effects play out in RNA and proteins that are made.
Mutations are changes in the genetic material of a cell.
Large scale: chromosomal and cause disorders or death
- nondisjunction, translocation, inversions, duplications, large deleters
Point mutations alter 1 base pair of gene.
Replace 1 base with another.
Different amino acid
Stop codon instead of amino acid.
Different 3rd letter (wobble), doesn't change AA
mRNA is read incorrectly, causing nonfunctional proteins. Caused by insertions of deletions.
Sickle Cell Disease
Caused by genetic defect, carried by 5% of humans, up to 25% in some regions of Africa.
Point mutation that forms long, inflexible chains.
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