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What is RNA?
- When we talk about nucleic acids, we list
two types: DNA and RNA, but what is
RNA?
- Structure is a “cheap copy” of DNA
- Bases A, G, C, U
- Thymine is replaced with Uracil (A = U T)
- Sugar is ribose not deoxyribose (less stable, takes less energy to make)
Types of RNA
- mRNA – messenger RNA
- carries copy of genetic instructions to the rest of the cell
- the instructions tell the cell how to assemble the amino acids for making proteins
- rRNA – ribosomal RNA
- makes up a part of ribosomes (which are the site for protein synthesis)
- tRNA – transfer RNA
- transfers each amino acid to the ribosome as it is specified by the mRNA
Protein Synthesis Quick Questions
QQ#2:
Where is DNA stored and where does DNA replication take place?
QQ#3:
How do you create a protein?
What is Protein Synthesis?
Making Proteins in order to express genes from the genetic code.
Overview:
(in cytoplasm) (in nucleus)
Two Important Steps
Step 1: Transcription : RNA synthesis from DNA DNA RNA Step 2: Translation : assembling protein from RNA RNA Proteins
How Does Protein Synthesis/ Gene Expression Occur?
Step 1: Transcription
- Simply:
- In the nucleus DNA mRNA
- This copy is used in step 2: translation
Step 1: Transcription
- RNA polymerase (an enzyme) – binds to DNA and
separates the 2 strands
- RNA polymerase then uses one strand of DNA as a
template for assembling an mRNA complementary
strand
- This creates a strand of mRNA which can carry the
genetic code out of the nucleus to complete the
second step of protein synthesis.
Step 2: Translation
- Simply:
- mRNA polypeptide chain (protein)
- mRNA is read in “codons” and is matched with tRNA antiocodons to link amino acids
Step 2: Translation Continued
- Process
- mRNA leaves nucleus and enters cytoplasm
- ribosomes (rRNA) binds to start sequence (AUG) on mRNA
- mRNA is read by ribosome 3 nucleotides at a time (called codons)
- Each codon codes for a specific amino acid
Step 2: Translation Continued
- Process
- Each codon on mRNA is read and a tRNA with the matching anti-codon carries the correct amino acid to the ribosome
- There, the tRNA binds to the ribosome and the amino acid is linked to the previous one by a peptide bond
- Process continues, amino acids are linked, and the polypeptide chain grows until the ribosome reaches the “stop” codon
- Protein is completed and folds into its structure
Translation-visual
- QQ#6: After watching the video and seeing
the images on the previous two slides,
summarize what occurs during translation
http://www.youtube.com/watch?v= 5bLEDd-PSTQ&feature=related start at 48 seconds
More pictures…because they are better than words…
