chapter 12-3 rna & protein synthesis notesnewburyparkhighschool.net/stillwagon/biocp/current...
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Chapter 12-3 RNA & Protein
Synthesis Notes
From DNA to Protein
(DNARNAProtein)
I. Review
A. Cells copy their DNA (in S phase of
Interphase)-Why? Prepare for Cell Division
(Mitosis & Cytokinesis)
Genes contain instructions for
assembling
1. purines.
2. nucleosomes.
3. proteins.
4. pyrimidines.
purines.
nucleoso
mes.
prote
ins.
pyrim
idin
es.
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B. The job of the cell is to make proteins!
C. The instructions are encoded in genes (DNA)
D. What is the process called that uses protein
instructions encoded in DNA to make
proteins???????
1. Protein Synthesis!
II. Protein Synthesis Overview
A. Occurs in 2 phases: Transcription and
Translation
B. With the help of RNA = Ribonucleic acid
1. RNA is a disposable copy of DNA segment
(coded DNA instructions that control the
production of proteins within the cell)
2. A RNA molecule is a working copy of a
single gene
3. The ability to copy a single DNA sequence
into RNA makes it possible for a single gene
to produce hundreds or even thousands of
RNA molecules.
III. RNA Structure & Types
A. Like DNA, RNA is also a polymer of
nucleotides (monomer); each consists of:
1. Simple sugar (ribose)
2. Phosphate group
3. Nitrogenous base
a. Four nitrogenous bases exist:
i. Adenine (A)
ii. Uracil (U)
iii. Cytosine (C)
iv. Guanine (G)
B. In RNA, Adenine (A) pairs with Uracil (U);
and Cytosine (C) pairs with Guanine (G)
C. While DNA is double stranded, RNA has just
one strand = single stranded
RNA contains the sugar
1. ribose.
2. deoxyribose.
3. glucose.
4. lactose.
ribose
.
deoxyrib
ose.
gluco
se.
lact
ose.
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D. 3 differences of RNA compared to DNA
1. Sugar= ribose; not deoxyribose
2. Single stranded not double stranded
3 RNA uses uracil (U); DNA uses the base
thymine (T)
A base that is present in RNA but
NOT in DNA is
1. thymine.
2. uracil.
3. cytosine.
4. adenine.
thym
ine.
uracil
.
cyto
sine.
adenine.
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How many main types of RNA are
there?
1. 1
2. 3
3. hundreds
4. thousands
1 3
hundreds
thousa
nds
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E. 3 types of RNA:
1. mRNA (messenger RNA) - carries info from
nucleus (copies from DNA) to the ribosomes
in a three letter genetic code = codon
2. tRNA (transfer RNA) – brings specific
amino acids to ribosomes by matching
mRNA; three nitrogenous bases that are
complementary to codon = anticodon
3. rRNA (ribosomal RNA) – structural and
functional part of ribosomes
So…. One more time….
Protein Synthesis has 2 major phases…..
Transcription
Translation
IV. Phase #1 (of 2) of protein synthesis: RNA
Transcription (DNA RNA): occurs in
nucleus of the cell
A. Transcribe: to make a copy
1. DNA instructions (encoded in genes) is
transcribed into mRNA
2. mRNA can leave the nucleus and go to
ribosomes in the cytoplasm
Eukaryotes
Prokaryotes
http://www.nature.com/scitable/content/local-remodeling-of-chromatin-for-transcription-44673 http://flylib.com/books/en/2.643.1.281/1/
When DNA is wrapped
around histones (forming
a nucleosome), DNA can
not be transcribed into
RNA
3. Special base sequences in DNA are
recognized by an enzyme as “start” and
“stop” signals
a. “Start” sequence called promoter region of
DNA
b. “Start” Codon = AUG (Methionine)
B. Details of the
Process
1. Step 1: RNA
polymerase
attaches to DNA at
the promoter
region (site where
DNA code signals
“start copying
here”). “Unzips” –
separates the 2
DNA strands.
2. Step 2: RNA polymerase moves along the
DNA strand (uses only 1 strand as a
template).
a. It synthesizes the mRNA strand by adding
new free RNA nucleotides (complementary
A-U; C-G)
b. Remember…there aren’t “T” bases in RNA
i. “C” binds with “G”
ii. “A” of the DNA binds with “U” of the RNA
c. Additional Information (if you were curious)
The antisense strand of DNA is read by RNA
polymerase from the 3' end to the 5' end during
transcription (3' → 5'). The complementary RNA is
created in the opposite direction, in the 5' → 3'
direction, matching the sequence of the sense strand.
This directionality is because RNA polymerase can
only add nucleotides to the 3' end of the growing
mRNA chain. This use of only the 3' → 5' DNA
strand eliminates the need for the Okazaki fragments
that are seen in DNA replication. This removes the
need for an RNA primer to initiate RNA synthesis, as
is the case in DNA replication.
http://www.universitario.com.br/celo/posts/trans
cricao/transcription.swf
Covalent Bonds Form
between nucleotides 5’ 3’
direction
RNA polymerase can only
add nucleotides to the 3' end
of the growing mRNA chain
What is produced during
transcription?
1. RNA molecules
2. DNA molecules
3. RNA polymerase
4. proteins
RNA mole
cule
s
DNA mole
cule
s
RNA poly
mera
se
prote
ins
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3. Step 3: When RNA polymerase reaches the
end of the gene, or "STOP" code on the DNA,
it detaches from the DNA
a. Completed mRNA strand (single stranded)
peels away (rate: 60 nucleotides
added/second)
4. Step 4: DNA re-zips (hydrogen bonds
reform)
5. Step 5: RNA is then edited; introns are
removed and exons are spliced together
a.Introns-sequences of nucleotides in DNA that
are not involved in coding for proteins
b. Exons-DNA sequences that code for
proteins; they are “expressed” in the
synthesis of proteins
snRNPs (small nuclear ribonucleoprotein particles,
complexes of snRNAs and proteins)
A region of a DNA molecule that indicates to
an enzyme where to bind to make RNA is the
1. intron.
2. exon.
3. promoter.
4. codon.
intro
n.
exon.
prom
oter.
codon.
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6. Step 6: Edited mRNA leaves the nucleus and
goes to a ribosome in the cytoplasm (End of
Transcription)
46
Which strand was copied? A or B
YES, Strand B. How do you know?
Which of the following are copied
from DNA?
1. mRNA only
2. mRNA, tRNA, and rRNA
3. mRNA and tRNA only
4. proteins
mRNA o
nly
mRNA, t
RNA, and rR
NA
mRNA a
nd tRNA o
nly
prote
ins
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V. The Genetic Code
A. Proteins are made by joining amino acids
into long chains called polypeptides.
1. The language of mRNA instruction is called
the genetic code.
2. The code is written in a language that has
only 4 letters (A, C, G, U).
3. Each “word” in the language is only 3
bases long
4. Codon = three consecutive nitrogenous bases
that specify a single amino acid (3 letter
words).
a. There are “start” (AUG) and “stop” (UGA,
UAA, or UAG) codons (Fig. 12-17)
Example of RNA Sequence: UCGCACGGU
Codons = UCG-CAC-GGU
The amino acids = Serine - Histidine - Glycine
5. If AUG is the start codon, what amino acid
will always be at the beginning?
a. Start codon = Methionine
6. Use the chart to identify the amino acid for
the codons below.
a. UAA =
b. CGA =
c. CUU =
d. UGU =
e. CCG =
Stop
Arginine
Leucine
Cysteine
Proline
7. You try!
Separate the RNA strand below into codons:
AUGGCUAACUAA
AUG-GCU-AAC-UAA
AUG-GCU-AAC-UAA
What is the amino acid sequence (Use chart)
Methionine (start) –Alanine –Asparagine– Stop