Unit 2 - 8. Gene Expression: Transcription and Translation Flashcards Preview

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Flashcards in Unit 2 - 8. Gene Expression: Transcription and Translation Deck (20):
1

Gene expression

- DNA does this by coding for proteins in the body using RNA as intermediate

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Central Dogma

DNA -(Transcription)-> RNA -(Translation)-> Protein

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Transcription

- DNA converted to complementary base sequence of mRNA in nucleus

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Translation

mRNA converted to linear sequence of amino acid = protein

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Promoter sequence

- a specific sequence of nucleotides in the 5' flanking region of DNA that RNA polymerase binds to

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Sense Strand

- "coding strand", complementary to the antisense strand and is the same sequence of the mRNA that will undergo translation

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Antisense strand

- aka missense strand
- read 3'-5' in transcription to make mRNA

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Exon

- sequences that are expressed (code for protein)

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Intron

- non-coding (intervening) sequences
- 90% of gene are introns

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Splicing

- removal of introns and joining together of exons

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codon

- set of 3 nucleotide that code for one amino acid

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anticodon

- 3 nucleotides in tRNA complementary to codon sequence on mRNA

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Transcription

- Initiation = RNA polymerase binds to promoter sequence (requires transcription factors) and the DNA helix unwinds.

- Elongation = RNA polymerase reads the anti-sense strand (3'-5') and adds nucleotides (ATP, GTP, CTP, UTP) to 3' end (builds 5' - 3')

- Termination = elongation stops when termination sequence in DNA is reached. mRNA and RNA polymerase release, DNA returns to its normal structure

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mRNA processing

- pre-mRNA includes exons and introns, splicing must take place to remove this
+ further modification:
1. addition of guanosine cap (5')
2. poly- A tail (3')
- creates stable mRNA to be transported from Nucleus to cytoplasm

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Reverse transcriptase

RNA (retrovirus) -(reverse transcriptase enzyme)-> cDNA -(RNA polymerase)-> mRNA

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Properties of Codons

1. Codons are degenerate (more than one codon can code for an Amino acid)
2. Amino acids with similar chemical properties have related codons
3. The code is nearly universal (all organisms use same codons)

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Translation

Initiation: (forms initiation complex)
- mRNA binds to small subunit of ribosome
- tRNA carrying start codon binds to mRNA
- large ribosomal subunit binds

Elongation:
- other tRNAs with matching next anticodon adds one at a time as ribosome shifts down and peptide binds form between amino acids

Termination:
- elongation stops when stop codon is reached (because there is no tRNA with an anticodon complementary to stop codon)
- peptide is released from ribosome

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Regulation of Gene Expression: DNA Level

DNA methylation to cytosine bases - condenses chromatin and prevents binding of transcription factors

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Regulation of Gene Expression: Transcription Level

- Chromatin remodeling (of histones to make promoters accessible or not )
- alternate splicing
- post transcriptional regulation via siRNA = RNA interference cleaves mRNA

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Regulation of Gene Expression: Translation Level

- length of poly A tail (longer = increased production rate)
- post-transational modifications = folding, adding lipids/carbs, modify/removing amino acids
- control of protein break down