NOTES: 13.1-13.2 - RNA & Protein Synthesis
Genes and Proteins:
● RECALL: the sequences of nucleotides in DNA contain
!
● This information is put to work through the production of
.
What do proteins do for the body?
● Proteins are diverse:
 control chemical messages in cell;
 direct the synthesis of carbo’s, lipids, and nucleotides;
 enzymes;
 give the cell structure and movement
● Goal of protein synthesis:
Protein Structure:
● RECALL: proteins are polymers of
● The sequence of nucleotides in each GENE contains the information for the sequence of AMINO
ACIDS in a single protein
● Each human cell contains about
genes
RNA
● Like DNA= made of
● copy of DNA segment
● 3 main types:
,
,
● 3 differences
1) sugar =
2)
3) instead of the base thymine (T),
Role of RNA – an analogy
● Imagine what goes into a new car being built on an automobile assembly line:
1) Engineers make the design and tell the workers how to make the cars;
2) Workers follow the directions to build the cars;
3) Suppliers bring parts to the assembly line so they can be installed in the car
● Now imagine what goes into PROTEIN SYNTHESIS:
1) DNA provides the “workers” with the instructions for making proteins;
2) The workers (RNA molecules!) follow the instructions from DNA and build the proteins;
3) Other workers (other RNA molecules) bring parts (AMINO ACIDS) over to the assembly line
3 Types of RNA:
1)Messenger RNA (mRNA): brings information from the DNA in the nucleus out to the ribosomes;
2)Ribosomal RNA (rRNA): clamp on to the mRNA and use its information to assemble amino acids into
a protein;
3)Transfer RNA (tRNA): the “supplier”;
to the ribosome
DNA  RNA
● How does the information in DNA , which is found in the nucleus, get out to the ribosomes in the
cytoplasm…it needs a “MESSENGER”!
TRANSCRIPTION
● Step #1 (of 2) of protein synthesis
● Transcribe:
● transcribing DNA information (gene instructions) into mRNA
-mRNA can leave the nucleus  goes to
● special base sequences in DNA are recognized by RNA as “start” and “stop” signals
-“Start” sequence called
region of DNA
Details of the Process
1.
attaches to DNA at the site where
instructions for the needed protein begins & it
the 2 DNA strands
2. RNA polymerase synthesizes the mRNA strand
using
● Remember…there aren’t “T” bases in RNA
● “C” binds with “G”
●
3. when RNA polymerase reaches the end or
releases.
part of the genetic code for that protein, it
4.
5. finished mRNA (message) leaves the nucleus and
● Bases are grouped by 3
● Called a
(“code”)
● Transcription ends with mRNA which will exit the nucleus to the cytoplasm
● So… if transcription is the first step of Protein Synthesis, what happens next in the cytoplasm?
TRANSLATION:
● Making a protein (string of amino acids): translating from the language of nucleic acids into a
polypeptide
● How does it go from mRNA (copy of DNA) to amino acids (building blocks of proteins)?
 A group of 3 mRNA bases makes up a “
” (think of as a “code word”)
 each codon specifies a particular
 there are “start” and “stop” codons
The Mechanism:
1) mRNA attaches onto the
 3 nucleotides of mRNA = codon
● 2nd kind of RNA= ribosomal RNA (rRNA)
 makes up the
● 3rd kind of RNA= transfer RNA (tRNA)
 carries amino acids to the ribosomes (amino acids join together)
 3 nucleotides of tRNA that “match” or compliment the mRNA =
 there are 64 different tRNA molecules (more than 1 for each amino acid)
 REDUNDANCY of the CODE!!
2) By matching the
acid is put into place
of mRNA to the
3) a
is formed between the
of tRNA, the correct amino
4) protein chain continues to grow until
 no tRNA exists for “stop” codons
● Molecules of tRNA are
-one end of tRNA attaches to a specific amino acid
-the other end attaches to mRNA codon by base pairing
**(anticodon =
)
● tRNA’s
**table 13.6 on page 367 shows the “dictionary” for the codons and their corresponding amino acids.
PRACTICE:
DNA: T A C C G C G G T T T A A C T
mRNA:
amino
acids: