Download Chapter 13.1 and 13.2 RNA, Ribosomes, and Protein Synthesis

Chapter 13.1 and 13.2 RNA,
Ribosomes, and Protein Synthesis
Remember ribosomes???
Our goal is to learn how proteins are made.
Keep in mind – amino acids are the building blocks
of proteins.
A chain of amino acids are “polypeptides” .
Role of RNA
• Ribonucleic acid (RNA) like DNA, but the bases
direct protein production.
• Proteins result in phenotypic traits.
• Differences b/t DNA & RNA
– RNA sugar ribose not deoxyribose
– RNA single strand not 2.
– RNA has uracil not thymine
RNA molecules make proteins
3 types of RNA
• 1. Messenger RNA(mRNA)- carries instructions for
polypeptide from nucleus to ribosomes in cytoplasm.
mRNA
RNA molecules make proteins - 3 types of RNA continued….
• 2. Ribosomal RNA (rRNA) – cell structures where
proteins are assembled
• 3. Transfer RNA (tRNA) – carries amino acids to
ribosome and matches them to the mRNA
message.
tRNA
mRNA
rRNA
RNA Synthesis
• Making RNA happens in “Transcription”
• Segments of DNA are templates to produce
RNA. The bases complement each other.
• Eukaryotes – happens in nucleus and moves to
cytoplasm to produce protein.
Steps to Make RNA
• 1. The enzyme RNA polymerase binds to DNA
during transcription and separates DNA. 1 strand
is the template.
• 2. RNA polymerase binds to promoter regions of
DNA. (START)
• RNA is edited. Introns cut out, Exons are left and
spliced back together to form mRNA.
The Genetic Code
• DNA has directions for making polypeptides
(aka chain of amino acids).
• The order and type of amino acids in the
polypeptide determine the protein.
• 4 bases – A,C,G,U for uracil
• Code is read 3 letters at a time the word is a
codon.
mRNA bases
• Amino
acids
• Codons
(3 letters
read in to
out)
• AUG =
Methionine
Translation
• Ribosomes use the codons in mRNA to assemble
amino acids to a polypeptide chain or protein.
• Process of decoding mRNA to protein is
“Translation”.
– mRNA transcribed (transcription) in nucleus goes to
cytoplasm.
– On ribosome, translation begins at START codon.
– Each codon attracts an anticodon aka tRNA
– tRNA carries an amino acid.
– Amino acids bond and move along the mRNA
– Continues until reaches STOP codon and forms
polypeptide and mRNA is released.
Translation &tRNA - anticodons
Molecular Basis of Heredity
• Molecular biology tries to explain living organisms
using molecules like DNA/RNA
• Central dogma of molecular biology is info is
transferred from DNA to RNA to proteins.
• Instructions for making proteins are in the genes.
• Gene expression is the way in which DNA, RNA,
proteins are involved in putting genetic info into
action in living cells.
• The genetic code is generally the same in all
organisms.