Bio 14.1 142 LESSON

14.1 RNA

Learning Objectives

▪ Describe how RNA differs from DNA.
▪ Explain how the cell makes RNA.

Comparing RNA and DNA

▪The sugar in RNA is
ribose instead of
deoxyribose.
▪RNA is generally
single-stranded, not
double-stranded.
▪RNA contains uracil
in place of thymine.

Multiple Select

Which of these describe RNA but not DNA?

• single stranded

• double stranded

• contains uracil

• contains adenine

• sugar is deoxyribose

Types of RNA

The three main types of RNA are:
•Messenger RNA
•Ribosomal RNA
•Transfer RNA

Messenger RNA

▪ An mRNA molecule is a copy of the portion of DNA that will be

used to make a protein.

▪ After being made in the nucleus, mRNA travels to the

cytoplasm, the site of protein synthesis.

Multiple Choice

The m in mRNA stands for messenger because mRNA

• takes the message of DNA out of the nucleus

• takes the message of amino acids into the nucleus

• takes the message of RNA into the nucleus

• takes the message of amino acids out of the nucleus

Ribosomal RNA

▪ Protein synthesis occurs on ribosomes, which are made up of

two subunits.

▪ These subunits consist of several molecules of ribosomal RNA

(rRNA) and as many as 80 different proteins.

Multiple Select

Which TWO of these are true of ribosomes?

• Ribosomes are made of TWO tRNA subunits

• Ribosomes are made of TWO mRNA subunits

• Ribosomes are made of TWO rRNA subunits

• Protein synthesis happens at the ribosome

• DNA replication happens at the ribosome

Transfer RNA

During protein synthesis, transfer RNA molecules (tRNA)
carry amino acids from the cytoplasm to the mRNA.

Labelling

Label the three types of RNA in the diagram.

Drag labels to their correct position on the image

tRNA

mRNA

rRNA

RNA Synthesis: Transcription

In transcription, segments of DNA serve as templates to
produce complementary mRNA molecules.

Drag and Drop

During ​

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, ​

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is used to make ​

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.

Drag these tiles and drop them in the correct blank above

transcription

DNA

mRNA

translation

tRNA

rRNA

RNA Synthesis: Promoters

RNA polymerase binds only to regions of DNA that have specific
base sequences. These regions are called promoters.

Multiple Choice

RNA polymerase is an enzyme that makes mRNA from DNA.

How does RNA polymerase know where to attach to copy a gene?

• It attaches at a PROMOTER - located at the BEGINNING of a gene.

• It attaches at a PROMOTER - located at the END of a gene.

• It attaches at a START CODE - located at the BEGINNING of a gene.

• It attaches at a STOP CODE - located at the END of a gene.

RNA Synthesis: RNA Editing

New RNA molecules sometimes require a bit of editing
before they are ready to be read.

Introns

Exons

Cap

Tail

Multiple Select

How is a new mRNA strand edited?

• introns are cut out

• introns are left in

• exons are cut out

• exons are left in

14.2 Ribosomes and Protein
Synthesis

Learning Objectives

▪ Explain how the genetic code works.
▪ Describe the role of the ribosome in assembling proteins.
▪ Understand how molecular biology relates to genetics.

The Genetic Code: Codons

▪ The genetic code is read in three-letter groupings called

codons.

▪ A codon is a group of three nucleotide bases in

messenger RNA that specifies a particular amino acid.

AUG

AAC

UCU

Multiple Select

Which 2 about codons are true?

• Codons are a set of 3 nucleotides

• Codons are a set of 3 amino acids

• Codons are a set of 5 nucleotides

• Each codon specifies 1 amino acid

• Each codon specifies 1 protein

Genetic Code Table

There are 64 possible three-base codons in the genetic
code.

Multiple Choice

How many possible codons are there?

• 3

• 25

• 64

• 128

• too many to count

Reading Codons

Start at the middle of the circle with the first letter of the codon and
move outward.

CAC = Histidine

Multiple Choice

How do you read codons in the circle?

• clockwise

• counterclockwise

• from the middle to the outside

• from the outside to the middle

Start and Stop Codons

The methionine codon AUG serves as the “start” codon for
protein synthesis. There are three “stop” codons.

AUG =
methionine =
“start” codon

UAA, UAG,
and UGA
are “stop”
codons

Multiple Choice

What month does school START in?

• AUG

  August

• MAR

  March

• SEPT

  September

• DEC

  December

Translation

▪ Transcribed mRNA directs the translation process.
▪ Translation is the process that produces proteins by

decoding the sequence of mRNA codons.

Multiple Select

What is true about translation?

• it produces proteins

• it happens in the nucleus

• it happens in the cytoplasm

• it produces mRNA

Translation: Transfer RNA

Translation starts when a ribosome attaches to an mRNA
molecule. Then, tRNA molecules, carrying amino acids with
them, bind to mRNA codons.

anticodon

Reorder

Reorder the following

• a ribosome attaches to mRNA

• tRNA carries amino acids to mRNA

• anticodons on tRNA bind to codons on mRNA

1

2

3

• 1
• 2
• 3

Translation: The Polypeptide Assembly

The ribosome helps form a peptide bond. It breaks the bond
holding the first tRNA molecule to its amino acid.

Multiple Select

Which two are true about bonds during translation?

• peptide bonds form between amino acids

• peptide bonds form between codons and anticodons

• the bond holding the tRNA gets broken AFTER the amino acid bond forms

• the bond holding the tRNA gets broken BEFORE the amino acid bond forms

Translation: Completing the Polypeptide

The ribosome reaches a stop codon, releasing the newly synthesized
polypeptide and the mRNA molecule, completing the process of
translation.

Multiple Choice

What is the newly formed string of bonded amino acids called?

• nucleotide chain

• rRNA

• tRNA

• polypeptide

• Stop codon

The Roles of RNA in Translation

All three major forms of RNA—mRNA, tRNA, and rRNA—are
involved in the process of translation.

Match

Match the following

• brings amino acids to the ribosome

• brings instructions from nucleus to ribosomes

• forms the subunits of ribosomes

tRNA

mRNA

rRNA

• tRNA

• mRNA

• rRNA

Molecular Genetics

The central dogma of molecular biology is that information is
transferred from DNA to RNA to protein.

Reorder

What is the order of the central dogma of molecular biology?

Start >>>>> Finish

• DNA

• RNA

• Protein

1

2

3

• 1
• 2
• 3

Gene Expression

When a gene (segment) of DNA code is used to build a protein,
scientists say that gene has been expressed.