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Protein Synthesis. Honors Biology (grab a textbook). Protein Synthesis. Sometimes proteins need to be made but DNA is trapped inside nucleus How does the “ code” for making proteins get out ?. DNA ---> RNA---> Protein.

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protein synthesis

Protein Synthesis

Honors Biology (grab a textbook)

protein synthesis1
Protein Synthesis
  • Sometimes proteins need to be made but DNA is trapped inside nucleus
  • How does the “code” for making proteins get out?
dna rna protein
DNA ---> RNA---> Protein
  • 1. Transcription - DNA is a template or pattern for making RNA
  • 2. RNA moves outside nucleus through pores
  • 3. Translation– RNA directs assembly of amino acids to form proteins
transcription step 1
Transcription Step 1
  • RNA polymerase binds to a “promoter” on the DNA; says where to “start”
  • DNA starts unwinding
transcription step 2
Transcription Step 2
  • RNA polymerase adds free RNA nucleotides (bases that are complementary to those on DNA strand)
  • A mRNA strand forms
  • Only involves a specific gene on DNA strand, not entire strand
transcription step 3
Transcription Step 3
  • RNA polymerase reaches a “termination” signal; says “stop”
  • RNA is released and DNA rewinds
questions don t copy
Questions (don’t copy)
  • Where does transcription take place in the cell?
  • What is the product of transcription?
  • How much of the DNA strand is copied?
types of rna
Types of RNA
  • Messenger RNA (mRNA) - carries “code” from DNA out of nucleus to a ribosome
  • Ribosomal RNA (rRNA) - makes up ribosome; the place where proteins are made
  • Transfer RNA (tRNA) - carries amino acids to the ribosome so protein can be made
the genetic code
The genetic code
  • The sequence of bases on mRNA determines how amino acids are put together
  • Genetic code - 3 bases together determine a specific amino acid
  • 3 bases on a mRNAcalled a “codon”
how it works
How it works
  • Page 207
  • AUG on mRNA means “start”
  • If next bases are CAC, this codes for Histidine
  • If next bases are AGC, this codes for Serine
  • Are 3 “stop” codons
translation making proteins
Translation (making proteins)
  • mRNA comes from nucleus and goes to a ribosome
  • If DNA code is: ATACGG
  • Then mRNA code is: UAUGCC (remember U is found in RNA, not T)

Chargaff’s Rule:

A pairs with T (or U)

C pairs with G

translation step 1
Translation – Step 1
  • mRNA moves along a ribosome
  • A tRNA arrives - on one end is the amino acid, on other end is anti-codon
  • codonof mRNA matches up to anticodon of tRNA (complementary)
translation step 2
Translation – Step 2
  • Codon & anti-codon meet; tRNA releases amino acid
  • Next tRNAarrives; codon & anti-codon meet; another a.a. is released and forms peptide bond with adjacent a.a.
translation step 3
Translation – Step 3
  • Enough amino acids bind together to form a polypeptide chain until a “stop” codon is reached
  • Chain falls off and a protein is made
example
Example
  • Original DNA = A-A-T-T-C-C-A-T-G
  • mRNA = U-U-A-A-G-G-U-A-C
  • tRNA= A-A-U-U-C-C-A-U-G
  • Amino acids the mRNA codon codes for:
    • UUA = leucine
    • AGG = lysine
    • UAC = tyrosine
now you try
Now you try…
  • Original DNA = G-C-T-T-A-G-C-T-A
  • mRNA =
  • tRNA =
  • Amino acids the mRNA codon codes for:?
answers
Answers
  • Original DNA = G-C-T-T-A-G-C-T-A
  • mRNA = C-G-A-A-U-C-G-A-U
  • tRNA = G-C-U-U-A-G-C-U-A
  • Amino acids the mRNA codon codes for:
    • C-G-A = arginine
    • A-U-C = isoleucine
    • G-A-U = aspartic acid
another one
Another one…
  • Original DNA =
  • mRNA = C-U-U-A-A-G-C-A-C
  • tRNA =
  • Amino acids the mRNA codon codes for:?
answers1
Answers
  • Original DNA = G-A-A-T-T-C-G-T-G
  • mRNA = C-U-U-A-A-G-C-A-C
  • tRNA = G-A-A-U-U-C-G-U-G
  • Amino acids the mRNA codon codes for:
    • C-U-U = leucine
    • A-A-G = lysine
    • C-A-C = histidine
one more
One more…
  • Original DNA =
  • mRNA =
  • tRNA = C-C-G-U-U-A-U-G-A
  • Amino acids the mRNA codon codes for:?
answers2
Answers
  • Original DNA = C-C-G-T-T-A-T-G-A
  • mRNA = G-G-C-A-A-U-A-C-U
  • tRNA = C-C-G-U-U-A-U-G-A
  • Amino acids the mRNA codon codes for:
    • G-G-C = glycine
    • A-A-U = asparagine
    • A-C-U = threonine
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