Transcript RNA & Protein Synthesis

What makes you look like your parents?
Your parents passed down their
DNA to you.
What’s carried in your DNA that
gives you your traits &
characteristics?
GENES!
What is a gene?
• A gene is a set of DNA instructions that control the
production (synthesis) of proteins within the cell.
DNA
Protein
DNA  Protein
• So, to express our traits, our cells need to convert DNA
into proteins.
How do we convert 1 macromolecule into another?
Nucleic Acid
Protein
Converting DNA into Protein
• This process, protein synthesis, involves 2 steps:
– Transcription
– Translation
RNA is the link between DNA & protein!
• DNA is found in the nucleus of cells, but proteins are built
in the cytoplasm.
• DNA cannot leave the nucleus, so a copy of the gene is
made in the form of a similar nucleic acid called RNA
(ribonucleic acid) during transcription.
• The RNA leaves the nucleus, attaches to a ribosome &
then is used to make a protein during translation.
RNA & Protein Synthesis
The Central Dogma of Biology
DNA  RNA  Protein
What is RNA?
• RNA is very similar to DNA:
– RNA is a nucleic acid macromolecule.
– RNA is made of nucleotides.
• Do you remember the 3 parts of a
nucleotide?
– 1 5-carbon sugar
– 1 phosphate group
– 1 nitrogenous base
DNA vs. RNA
• RNA contains the sugar
ribose, while DNA
contains the sugar
deoxyribose.
• RNA is single stranded,
while DNA is double
stranded.
DNA vs. RNA
• RNA contains uracil
instead of thymine.
• Both DNA & RNA have
adenine, cytosine, &
guanine.
RNA – 3 Types
• Messenger RNA (mRNA): acts as a messenger &
carries a copy of the information in DNA to the
ribosome where proteins are made
RNA – 3 Types
• Ribosomal RNA (rRNA): found within ribosomes;
ribosomes are made of both proteins & rRNA
RNA – 3 Types
• Transfer RNA (tRNA):
brings amino acids to the
ribosome to be added to
the protein chain that is
being made
– There is 1 tRNA for each of
the 20 amino acids.
The 20 Amino Acids that Build Proteins
Why are proteins important?
& how do they give us our traits?
Each protein has a specific function within
living cells.
• Can be enzymes, to speed up & regulate chemical
reactions
• Making pigments that determine flower color in plants
• Determine your blood type
• Regulate cell growth & development
• Lactose is the sugar found in milk
(disaccharide).
• When your body digests lactose, it
gets broken down into glucose &
galactose (monosaccharides).
• Lactase is the enzyme that breaks
down lactose.
– Enzymes are proteins!
Lactose Intolerance
• People who are lactose intolerant have a mutation in the
gene that codes for lactase.
• Since they don’t produce lactase, they can’t digest lactose.
Protein Synthesis
DNA  RNA  Protein
• Protein synthesis (making
proteins from your genes)
occurs in 2 steps:
– Transcription
– Translation
Protein Synthesis – Transcription
DNA  RNA  Protein
• Genes carry the instructions to build a protein.
• DNA is located in the nucleus, but proteins are built in
the cytoplasm.
• We need to make a copy of the instructions in the form
of RNA (transcription).
– RNA can leave the nucleus & take the instructions to the
ribosomes.
Transcription
• The process in which the nucleotide sequence of DNA is
copied into a complementary sequence of RNA
– Occurs in the nucleus
– DNA  mRNA  Protein
Transcription – Step 1
• The enzyme RNA Polymerase binds to the DNA in the
nucleus & breaks the hydrogen bonds between the 2
strands.
Transcription – Step 2
• Using 1 strand of DNA as a template, RNA Polymerase
adds nucleotides 1 by 1 & forms the new mRNA strand.
Transcription – Step 3
• When transcription is
complete, the mRNA leaves
the nucleus through the
nuclear pores & enters the
cytoplasm of the cell.
DNA is like the “master plan” & mRNA is like
the “blueprint”.
• The master plan stays in the office (the nucleus) & the
blueprint can be taken to the construction site (the
ribosome).