Transcript DNA and Proteins

Chapter 11
DNA and Genes
Section 2
From DNA to Protein
•Proteins
• Form
structures and control chemical
reactions in cells.
• Polymers of amino acids.
• Coded for by specific sequences of
nucleotides in DNA.
•Exons
• Regions
of genes that contain
information.
•Introns
• Long
noncoding nucleotide sequences
located in genes.
•RNA
• Nucleic
acid.
• Single stranded.
• Formed from a phosphate group, the
sugar ribose, and four nitrogenous
bases (adenine, guanine, cytosine,
and uracil).
•Transcription
• Process
where enzymes make an RNA
copy of a portion of a DNA strand.
•RNA and Protein Synthesis
• RNA
uses the instructions provided by
DNA to assemble proteins, amino acid
by amino acid.
•Translation
• Takes
place at the ribosomes.
• The process of converting the
information in mRNA into a sequence
of amino acids in a protein.
•Three Types of RNA
1.
2.
3.
Messenger RNA
Ribosomal RNA
Transfer RNA
•mRNA
• Brings
instructions from DNA in the
nucleus to ribosomes located in the
cytoplasm where protein synthesis
occurs.
•mRNA
• Uses
a combination of three nitrogenous
bases, called a codon, to code for one
of 20 common amino acids.
There are 64 codons possible.
• Some codons code for instructions such as
start (AUG) and stop (UAA).
• The same amino acid can have more than
one codon.
•
•mRNA
• During
transcription, both introns and
exons are copied.
• However, the introns must be removed
from the mRNA by enzymes and the
resulting exon pieces pasted back
together before it the mRNA can move
out of the nucleus and function to
make a protein.
•rRNA
• When
mRNA reaches the ribosome,
rRNA binds to the mRNA and uses the
instructions provided to assemble the
amino acids in the correct order.
•tRNA
• Delivers
amino acids to the ribosome
where they are assembled into proteins.
• Each tRNA molecule attaches to only
one type of amino acid.
•tRNA
•A
sequence of three nucleotides,
called an anticodon, is located on the
side of the tRNA opposite the amino
acid attachment site.
• The anticodon of the tRNA binds to the
correlating codon on the mRNA,
insuring correct translation of the mRNA
message.
•Steps in Translation
1.
..\..\..\AP Bio\Bio in focus
PP\Chapter_14\C_Animations_and_
Videos\14_BioFlix_Animations\10_Pro
tein_Synthesis\PC\ProteinSynthesis.m
pg
•Steps in Translation
1.
2.
3.
A tRNA molecule brings the first
amino acid to the mRNA strand
which is attached to a ribosome.
The anticodon of the tRNA forms a
base pair with the corresponding
codon of the mRNA.
The ribosome slides down the mRNA
chain to the next codon.
•Steps in Translation
4.
5.
6.
A new tRNA molecule carrying a
second amino acid pairs with the
new codon.
The two amino acids that are now
adjacent to each other form a bond.
The first tRNA releases its amino acid
and detached forms the mRNA, in
order to bring another amino acid to
the chain.
•Steps in Translation
7.
8.
The ribosome slides down to the next
codon and the previous steps are
repeated.
This process continues, forming a
chain of amino acids, until a stop
codon is reached, where translation
ends and the amino acid chain is
released form the ribosome.
•Steps in Translation
Amino acid chains become proteins
when they are freed from the
ribosome and twist and curl into
complex 3-D shapes.
9.
•
Each protein chain forms the same
shape every time it is produced.