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?

DNA Transcription Video

Protein Synthesis Active Art-Resource Disk

Ch 12-3

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