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37 Cards in this Set
- Front
- Back
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Genes
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Make up a segment of DNA that code for a particular protein/enzyme and sometimes for RNA
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Stem cells
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• Unprogrammed / unspecialized cells
• genes aren't turned on or off |
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Are there different genes in different places of the body?
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• No, the same genes are located throughout the whole body
• genes are turned on or off in different places of the body depending on the functions of that location |
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Genotype and phenotype: which determines which?
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Genotype determines phenotype
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From DNA to mRNA is...
From mRNA to proteins is... |
From DNA to RNA is transcription
From RNA to proteins is translation |
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Transcription
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To make a copy of something
mRNA copies and carries DNA's information |
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Translation
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Translates the language of nucleic acids to that of proteins
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Differences between transcription and translation in prokaryotic and eukaryotic cells
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Prokaryote:
• no nucleus, so both processes occur in the cytosol • occur nearly at the same time, so is much faster Eukaryotes: • transcription occurs in nucleus • translation occurs in cytosol |
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Template strand
Which direction does it run in? (prime end) |
Template strand:
• DNA strand that is being transcribed • 3' - 5' • mRNA is antiparallel (complementary) to template; growing 5' - 3' |
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From DNA to pre-mRNA is...
From pre-mRNA to mRNA is... From mRNA to polypeptides is... From polypeptides to proteins is... |
From DNA to pre-mRNA is...transcription
From pre-mRNA to mRNA is...RNA processing From mRNA to polypeptides is...translation From polypeptides to proteins is...folding |
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Pre-mRNA
RNA processing (where it occurs) |
Pre-mRNA = RNA that is transcribed from DNA
RNA processing = process from pre-mRNA to mRNA; occurs in the nucleus |
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What organelles are involved with translation?
4 |
Places where proteins are made
Ribosomes Cytosol Mitochondria Chloroplasts |
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What are the types of RNA?
5 |
1) Messenger RNA = mRNA
2) Ribosomal RNA = rRNA 3) Transfer RNA = tRNA 4) Small nuclear RNA = snRNA 5) Signal Recognition Particle = SRP |
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Messenger RNA (mRNA)
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Translates information from DNA to direct the synthesis of polypeptide chains
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How many amino acids do the 4 nucleotides code for?
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20
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Codon
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• 3 nucleotides sequence on mRNA
• codes for 1 amino acid • there are 64 codons |
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Start codon
What is the sequence and what does it code for? What does it do and where? |
• AUG = methionine
• Signals the start of transcription in the ribosome • all proteins start with this |
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Stop codons
What is the sequence? What does it do and where? |
UAA
UAG UGA Signals the end of transcription in the ribosome |
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Wobble nucleotide
Why can this do what it does? (3) |
• the last nucleotide in a codon, at which if a mutation occurs it will be silent
• more than one codon can code for the same amino acid • all these will have the same first 2 letters, but different last letter • if the last letter changes it will still code for the same amino acid, but if one of the first 2 change it will code for the wrong amino acid |
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What happens if the wrong nucleotides are coded for in a codon?
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Mutations
If it they expressed the protein will fold incorrectly |
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RNA polymerase II
Does it need a primer? |
Separates DNA strands and polymerizes pre-mRNA
Does not need a primer to work |
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What is a transcription unit?
What is it composed of? |
Nucleotide sequences on the DNA where transcription occurs
1) A promotor 2) Transcription site/coding region 3) Terminator sequence |
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What is a promotor? (3)
What is its sequence? |
• Sequence of DNA where RNA polymerase binds to DNA to begin transcription
• located before start codon • promotor segment is not transcribed • sequence = TATAA |
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Elongation
By what process Bonds involved |
• RNA poly II adds free ribonucleotides to the growing chain on the 3' end by dehydration synthesis
• The ribonucleotides bond to their sugar-phosphate backbone by phosphodiester bonds • The ribonucleotides pairs with DNA nucleotides by hydrogen bonds |
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What unwinds the 2 DNA strands for transcription to occur?
What part of the DNA is this happening at? |
RNA polymerase II as it runs along the transcription unit
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Terminator
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• Sequence of DNA where RNA poly II stops transcribing and is released from DNA
• is not transcribed into mRNA |
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mRNA hairpin
What are the sequences and base pairs here? |
• when RNA poly II reaches the terminator sequence, mRNA loops into a hairpin by bonding to its own ribonucleotides → made up of G-C pairs
• followed by 4 uracils which bond to 4 adenines on DNA • A-U bond is very weak (just 1 hydrogen bond between them) so they break apart, causing the RNA-DNA hybrid dissociates |
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RNA processing
Where it occurs What it does 3 steps |
• Occurs only in eukaryotes in the nucleus
• transforms pre-mRNA into mRNA • 3 steps 1) addition of methylated cap 2) removal of introns 3) polyadenylation of the 3' end |
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Step 1 of RNA processing: Addition of methylated cap
When does it occur? What is a methylated cap? What is methylated? What is its function? (2) |
• occurs during transcription
• a methylated guanine added to 5' end of pre-mRNA • methylated = to add a methyl group CH3 • protects mRNA from degradation • aids attachment to ribosomes for translation |
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Introns
Exons |
Introns
• non-coding regions of DNA which are transcribed into pre-mRNA Exons • the coding regions of DNA which are transcribed into the pre-mRNA |
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Step 2 of RNA processing: Removal on introns
What is the result? |
• splicoesosomes remove introns and bind together exons
• pre-RNA has now become mRNA! |
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What splices out introns and joins exons?
What is this composed of? (2) |
Splicesome = a complex of small nucleoprotein particles (snRNP) and proteins that binds to intron-exon junctions
snRNP's are made up of small nuclear RNA (snRNA) |
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Step 3 of RNA processing: Polyadenylation
Functions (2) |
• Enzyme polyadenylase recognizes an AAUAA sequence on the mRNA's 3' end
• adds a poly A tail after sequence • poly A tail = many adenine ribonucleotides Functions • facilitates transport of mRNA through nuclear pores into cytoplasm • prevents degradation by hydrolytic enzymes |
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Transfer RNA (tRNA)
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• RNA looped and bound to itself, with an anticodon end and amino acid acceptor end
• anticodons are complementary to codons • there is 1 tRNA per codon |
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Aminoacyl-tRNA synthetase
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Enzyme that binds a tRNA to an animo acid at tRNA's acceptor end
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How are polypeptide chains built?
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1) mRNA enters ribosome
2) individual tRNA bind their anticodons to a complementary mRNA codon 3) an enzyme peptide bonds the amino acids bound to the tRNAs |
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Signal Recognition Particle (SRP)
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• consists of RNA and proteins
• binds to polypeptide chain that is emerging from a ribosome • guides the ribosome to the rough ER and threads polypeptide chain through the pores into the lumen |
