Structure and Function of RNA

RNA- ribonucleic acid

1. RNA is a single strand

2. RNA is made up of smaller subunits called nucleotides

3. Nucleotides consist of:A. Sugar-riboseB. phosphate group

C. nitrogen base-4 types1. Adenine-A2. Uracil- U3. Guanine- G4. Cytosine- C

4. Adenine(A) pairs with Uracil(U)and Cytosine(C) pairs with Guanine(G)

5. 3 kinds of RNA

A. messenger(m) RNA- carries nucleotide sequence from nucleus to ribosome

B. transfer(t) RNA-picks up amino acids in cytoplasm and carries them to

ribosome

C. ribosomal(r) RNA- found in ribosome, joins mRNA and tRNA

Process of transcription

1. Transcription- process that makes RNA (messenger RNA) from DNA

2. DNA unzips into 2 separate strands

3. Free floating RNA nucleotides in the nucleus pair up with these unzipped DNA nucleotides

A. Cytosine(C) pairs with Guanine(G) B. Uracil(U) pairs with Adenine(A)

4. After all the pairing is done, a single strand of RNA has been produced.

5. Genetic code from DNA is transferred to mRNA

6. The code obtained from DNA lets the mRNA know which amino acids to pick up

A. code is a set of 3 nitrogen bases B. called a codon

RNADNA

RNApolymerase

Figure 12–14 TranscriptionSection 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

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Process of Translation1. Translation- conversion of mRNA into

amino acid sequence that makes up a protein

2. Occurs at the ribosomes

3. The mRNA leaves the nucleus and enters the cytoplasm

4. Ribosomes attach to mRNA

5. The mRNA is read by ribosomes 3 nucleotides(codon- A G C) at a time

6. As the codons are read, tRNA brings the appropriate amino acids together and they are assembled in a long chain called a protein

7. The genetic code ultimately tells the cell what proteins are made

Translation

Messenger RNA

Messenger RNA is transcribed in the nucleus.

Transfer RNA

The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

Figure 12–18 TranslationSection 12-3

mRNA

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The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Figure 12–18 Translation (continued)

Section 12-3

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Quiz #4

RNA

1. RNA is single stranded, made up of ___________.

a. Proteins b. nucleotides c. thymines d. codons

2. Which nitrogen base for RNA does not belong?

a. Uracilb. adenine c. cytosine d. thymine

3. mRNA is made from DNA through a process called _______.

a. Replication b. translation c. transcription

4. Proteins are made from mRNA through a process called ____.

a. Replication b. translation c. transcription

5. If a sample of DNA is A-C-T-T-G-A, what would the strand of RNA produced be?

A. T-G-G-T-A-A

B. U-G-A-A-C-U

C. T-G-A-A-C-T