chapter 13 section 3: rna and gene expression - quia · pdf filechapter 13 section 3: rna and...

Adapted from Holt Biology 2008

Chapter 13 Section 3: RNA and Gene Expression

Key Vocabulary Terms

RNA

Ribonucleic acid, plays a role in protein

synthesis

Gene Expression

The manifestation of the genetic material of an

organism in the form of specific traits.

Gene expression produces proteins by

transcription and translation.

Transcription

The process of forming a nucleic acid (RNA) by using another molecule

as a template.

DNA is used to make RNA

Codon

In mRNA, the three-nucleotide sequence that codes for an amino acid, or signifies a start or

a stop signal


Chapter 13 Section 3: RNA and Gene Expression

Supplementary Words

Uracil (U)

An organic compound of the pyrimidine family that occurs as a component of

ribonucleic acid (RNA), bonds with adenine

Transfer RNA (tRNA)

An RNA molecule that transfers amino acids to the growing end of a polypeptide chain during

translation

Ribosomal RNA (rRNA) The RNA component of the ribosome (P site & A

site). Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts

with tRNAs during translation.

Messenger RNA (mRNA) A molecule of RNA encoding a chemical "blueprint"

for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the

sites of protein synthesis: the ribosome's.

RNA polymerase

An enzyme that starts (catalyzes) the formation of RNA by using a strand of a DNA molecule as a

template

Promoter

A nucleotide sequence on a DNA

molecule to which an RNA polymerase

molecule binds, which initiates the

transcription of a specific gene

Amino acids

Any one of 20 different organic molecules that contain a carboxyl and

an amino group and that combine to form

proteins

Genetic code

The rule that describes how a sequence of nucleotides specifies the amino acid

sequence of a protein

It is read in groups of three consecutive nucleotides

(triplets) that correspond to specific amino acids.

Polypeptide

A long chain of several amino acids

Anticodon

A region of tRNA that consists of three bases complementary to the

codon of mRNA

Stop codon

In an mRNA molecule, a sequence of three

nucleotides (UUA, UAG, and UGA) that does not encode an amino acid and therefore

stops protein synthesis


Chapter 13 Section 3:

RNA and Gene Expression

Notes

Central Dogma

–DNA makes more DNA by ____________

–DNA makes RNA by ___________

–RNA helps make protein by ___________.

Replication

Transcription

Translation

An Overview of Gene Expression DNA provides the original information from which proteins are made in a cell, but DNA does not directly make proteins.

Ribonucleic acid, or RNA, is a second type of nucleic

acid which takes the information from DNA and makes proteins.

Gene expression produces

proteins by transcription

and translation.

Both stages involve RNA.

Your Turn Activity

RNA: A Major Player

• All of the steps in gene expression involve RNA.

• In cells, three types of RNA complement DNA and translate the genetic code into proteins.

• Like DNA, RNA is made of nucleotide

subunits linked together.

RNA differs from DNA in 3 ways:

1st, RNA is composed of one strand of nucleotides

DNA= two strands


2nd, RNA nucleotides contain the five-carbon sugar ribose. DNA = deoxyribose


3rd, RNA nucleotides have a nitrogenous base called uracil (U) DNA = base thymine (T) Uracil (U) is complementary to adenine (A)

whenever RNA pairs with another nucleic acid.

There are 3 main types of RNA:

Messenger RNA (mRNA),

Transfer RNA (tRNA),

& Ribosomal RNA (rRNA).

Messenger RNA (mRNA) is produced when DNA is transcribed into RNA. Carries instructions for making a protein, and

delivers instructions.

Transfer RNA (tRNA) at the site of translation “reads” the instructions

carried by the mRNA, then translates the mRNA sequence into protein

subunits called amino acids.

Ribosomal RNA (rRNA) is an RNA molecule that is part of the structure of

ribosomes.

Ribosomes are the cellular structure where protein production occurs.

6

Transcription: Reading the Gene

During transcription, the information in a

specific region of DNA (a gene) is transcribed, or copied, into mRNA.


Transcription is carried out by a enzyme called

RNA polymerase.

2


Transcription begins when RNA polymerase binds to the specific DNA sequence in the

gene that is called the promoter.


RNA polymerase then unwinds and separates the two strands of the double helix to expose the DNA bases on each

strand.

RNA polymerase moves along the bases on the DNA strand and adds complementary RNA bases as it “reads” the DNA of the gene.


As RNA polymerase moves down the

DNA strand, a single strand of mRNA grows.


Behind the moving RNA polymerase, the two strands of DNA close up and

re-form the double helix.


Transcription = a new molecule of RNA is made from the DNA.

In DNA replication= a new molecule of DNA

is made from the DNA.

Transcription is not the same process as replication.

Transcription

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The Genetic Code: Three-Letter “Words”

• codon = three-nucleotide sequence in mRNA Each codon corresponds to 1 of 20 amino acids.

• Codons may act as a start or stop signal for translation.

6th


• There are 64 mRNA codons. Each codon specifies only one amino acid, but several amino acids have more than one codon.

• This system of matching codons and amino acids is called the genetic code. The genetic code is based on codons that each represent a specific amino acid.

4th,

7th


There are 64 mRNA codons. Each codon

specifies only one amino acid, but several amino acids have more than

one codon.

5th

Codons in mRNA

Translation: RNA to Proteins

• Translation – occurs in a sequence of steps, – involves three kinds of RNA – results in a complete polypeptide (protein).

• Translation takes place in the cytoplasm

• A specific amino acid is added to one end of each

tRNA. The other end of the tRNA has an anticodon.

• An anticodon is a three-nucleotide sequence on tRNA that is complementary to an mRNA codon.

4&5

Translation: RNA to Proteins, continued

• The mRNA joins with a ribosome and tRNA.

• A tRNA molecule that has the correct anticodon and amino acid binds to the second codon on the mRNA.

• A peptide bond forms between the two amino acids, and the first tRNA is released from the ribosome.

• The ribosome then moves one codon down the mRNA.

Translation: RNA to Proteins, continued

• The amino acid chain continues to grow as each new amino acid binds to the chain and the previous tRNA is released.

• This process is repeated until one of three stop codons is reached. – A stop codon does not have an anticodon, so

protein production stops.

• Many copies of the same protein can be made rapidly from a single mRNA molecule because several ribosomes can translate the same mRNA at the same time.

Translation: RNA to Proteins

Complexities of Gene Expression

• The relationship between genes and their effects is complex.

• Some genes are expressed only at certain times or under specific conditions.

• Variations and mistakes can occur at each of the steps in replication, transcription, and translation.

• The final outcome of gene expression is affected by – the environment of the cells – the presence of other cells – the timing of gene expression

A bundle of DNA is supported by two silicon pillars.

DNA's double-helix structure is on display for the first time in this electron microscope photograph of a small

bundle of DNA strands.

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