12-3: RNA AND PROTEIN SYNTHESIS

Biology 2

• DNA double helix structure explains how DNA can be copied, but not how genes work

• GENES: sequence of DNA that codes for a protein and thus determines a trait

• DNA must copy messages onto RNA

• RNA contains “codes” for making proteins

Introduction

• RNA is made of building blocks called nucleotides

• NUCLEOTIDES: monomer of nucleic acids made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base

• Can have 4 different types of base:–Adenine–Guanine–Uracil (replaces Thymine)– Cytosine

Structure of RNA

Ribose Sugar

• Backbone of RNA is sugar and phosphate groups

– FORM THE OUTSIDE

• Bases DO NOT bond together to connect inside

Components and

Structure of DNA

1. DNA uses deoxyribose– RNA uses ribose sugar in

nucleotides

2. DNA is double stranded– RNA is single stranded

3. DNA uses Thymine– RNA uses Uracil

Differences Between RNA and DNA

• 3 types of RNA:

• mRNA: carries messages to ribosomes

• tRNA: transfers amino acids to the ribosomes

• rRNA: make up different parts of the ribosome

Types of RNA

• TRANSCRIPTION: process in which part of the nucleotide sequence of DNA is copied into a complementary sequence in RNA

• DNA creates a temporary copy of messages on mRNA, its carried to ribosomes and tRNA carries amino acids for building the proteins

Transcription

• During transcription enzyme attaches to PROMOTER sequence (like a green light)

• Enzyme will read all bases on a DNA strand to make mRNA message

• Enzyme will stop at TERMINATOR sequence (like a red light)

Transcription

• Proteins are made by joining amino acids into long chains– 20 different amino acids possible

• Properties of proteins are determined by sequence (order) of amino acids

• The message mRNA carries is called the Genetic Code

The Genetic Code

• Each set of 3 bases on mRNA is known as a codon– CODON: three-nucleotide sequence

on messenger RNA that codes for a single amino acid

• Each codon has instructions for specific amino acid– Can have more than 1 codon for

each amino acid

The Genetic Code

• Sequence (order) of bases in mRNA are instructions for which amino acids should be joined in a specific order

• Creating the chain of amino acids is called translation– TRANSLATION: decoding of a

mRNA message into a polypeptide chain

• This is reading the mRNA message to figure out the order of amino acids

Translation

• Enzyme will read all bases on a DNA strand to make mRNA message–mRNA message is sent to

ribosomes• Ribosomes “read” the message• tRNA carries the amino acids

anti-codon matching the mRNA codon message to the ribosome

• Ribosome “glues” amino acids together to form protein chains

Translation

Protein Synthesis – Translation Process

http://www.youtube.com/watch?v=B6O6uRb1D38

Bill Nye – Genes and Chromosomes

http://www.youtube.com/watch?v=HqoQoJMG0Lc