​8th Grade Science Notes Unit 5: Protein Synthesis

​8th Grade Science Notes


Unit 5: Protein Synthesis

Protein synthesis

• DNA---> mRNA---> Protein
• DNA code is rewritten to mRNA

– A-->U, C→ G
– RNA does not have T it has U(uracil)
– mRNA goes to the ribosome and the ribosome

makes the protein.

RNA & Protein
Synthesis Notes

RIBONUCLEIC ACID

R.N.A. is also a nucleic
acid - it is made out of
linked nucleotides (like
DNA). Recall that
nucleotides are made
of a sugar, phosphate,
and nitrogen base.

DNA VS. RNA

RNA and DNA are
very similar, but there
are some differences.

First of all, DNA is
double stranded, and
RNA is single stranded.
This means that RNA is
SMALLER than DNA.

RNA contains 4 nitrogen bases: adenine, guanine, cytosine

and URACIL. *Thymine is NOT present in RNA.

Uracil is complementary to adenine in DNA. It
essentially takes the place of thymine.

The last major difference between DNA and

RNA is that RNA contains the 5-carbon sugar
ribose (recall that DNA contains deoxyribose).

Ribose has one more oxygen atom than

deoxyribose.

RECAP

RNA is single stranded, so it is smaller than

DNA, which means it can leave the nucleus
(while DNA cannot leave the nucleus).

RNA contains the sugar ribose.

RNA has 4 bases: A, G, C, and U. The base

pairing rules are as follows:

C pairs with G
G pairs with

C

A pairs with

U

U pairs with A

NO

thymine
in RNA

Multiple Choice

What type of sugar makes up RNA?

• deoxyribose

• glucose

• fructose

• ribose

Multiple Choice

What shape is RNA?

• single helix

• double helix

Multiple Choice

What base does RNA have that DNA does not?

• uracil

• thymine

• cytosine

• guanine

3 TYPES OF RNA

RNA’s job is to help DNA make proteins.

Since DNA cannot leave the nucleus, it must

deliver its code to the remainder of the cell - it
relies on 3 molecules:

1)

Messenger RNA (mRNA)

2)

Transfer RNA (tRNA)

3)

Ribosomal RNA (rRNA)

MESSENGER RNA

mRNA is complementary to the original strand of DNA.
mRNA is first created in the nucleus and then travels to

the ribosomes out in the cytoplasm.

The job of mRNA is to take the information that is stored

in the DNA and relay it to the ribosomes.

EX: DNA = desktop computer; mRNA = printed

instructions for the road trip

DNA Strand: G GCT T A
mRNA strand: C C GA A U

Multiple Select

There are 3 types of RNA. What are they? (Select all that apply)

• tRNA

• rRNA

• mRNA

• xRNA

Multiple Choice

RNA contains the sugar

• ribose

• deoxyribose

• glucose

• lactose

Multiple Choice

What is the template for mRNA?

• DNA

• tRNA

• rRNA

• proteins

CODONS

Individual DNA codes are called “codons”.
Codons consist of groups of 3 nucleotides called triplets.
The codons correspond to specific amino acids that are used to

build the needed protein.

mRNA also has codons, which are complementary to DNA

codons.

Example) DNA codon:

cytosine-cytosine-adenine

(CCA for short)

Each codon codes for one amino acid. This is where we need

RNA’s help.

C

C

A

DNA Template Strand:

A C G T T A G C C

mRNA strand:

U

G C A A U C G G

mRNA is always complementary to the template DNA

strand.

How many codons are there?

What does the other DNA strand look like?

Though there are only 20 different amino acids, they are
sequenced differently and come in different shapes to
make for thousands of different proteins.

CODONS

There are 64 possible

codons:

43 = 64

64 codons for 20 amino acids.

Can more than one codon specify the same amino acid?

4 possible bases

(A, T, C or G)

3 bases in a codon

(triplets)

Multiple Choice

Choose the sequence of the mRNA strand that would match up with to the following DNA strand:

GTACAT

• CATGTA

• GAUCUA

• CAUGUA

• CUTGTU

Multiple Choice

How many nucleotides code for 1 amino acid?

• 1

• 2

• 3

• 4

Multiple Choice

How many different amino acids are there?

• 10

• 18

• 20

• Thousands

Multiple Choice

Three nucleotides come together to form a

• enzyme

• Codon

• DNA

• RNA

This is the beginning step of PROTEIN

SYNTHESIS… meaning:

Protein= well, protein

synthesis= to make

In this process, DNA codons are transcribed

into mRNA codons. mRNA codons are
specific to different amino acids that are
linked together to make a protein. We will
also use two other kinds of RNA to complete
this process and make our desired protein.

PROTEIN SYNTHESIS DETAILS

• A two part process in which DNA is decoded

into corresponding proteins.

• The first process is known as transcription,

where DNA is rewritten in the form of mRNA so
that the information can leave the nucleus.

• The second process is translation, where the

ribosome with the help of tRNA translate the
information to make the protein.

• Occurs in both the nucleus(transcription) and

cytoplasm (translation).

TRANSCRIPTION

Transcription is the first part of

protein synthesis.

During transcription, mRNA is

created by transcribing the
DNA’s code, or rewriting it into
RNA.

Transcription occurs in the

nucleus.

(That’s where the DNA is!)

This is the step of taking the

instructions from MapQuest and
creating a hard copy to take with
you in the car to use for the trip.

Multiple Choice

The process of creating RNA using DNA as the template is

• translation

• transcription

• translocation

• Transylvania

Multiple Choice

What is the order for Protein Synthesis?

• Transcription -> Translation -> Protein

• Translation - > Transcription -> Protein

• Protein -> Transcription -> Translation

• Translation -> Protein -> Transcription

Multiple Choice

Where does transcription take place?

• at a ribosome

• in the nucleus

• at a mitochondria

• at a lysosome

TRANSCRIPTION

During transcription, the

enzyme RNA
polymerase temporarily
unzips DNA and adds
complementary RNA
nucleotides to the
growing mRNA strand.

Anywhere there is a T, it

will now be replaced with
a U.

TRANSCRIPTION

Recall that mRNA is the messenger. It copies DNA’s code (or

“message”; “instructions”) and it is now responsible for
delivering this message to the rest of the cell.

Once the mRNA strand is completed, it leaves the nucleus (exits

via nuclear pores) and transcription is complete.

(No protein yet...next stop, the ribosomes!)

TRANSLATION

Translation is the final step of protein synthesis - it involves

ALL THREE types of RNA (mRNA, tRNA and rRNA).

• Translation is a process in which the mRNA that was

manufactured during transcription is translated into an
amino acid sequence (proteins).

• occurs in the cytoplasm

and on the ribosomes

Multiple Choice

What is the correct order to make a protein?

• Protein, DNA, RNA

• RNA, DNA, Protein

• DNA, RNA, Protein

• Protein, RNA, DNA

Ribosomal RNA (rRNA)= a major

component of ribosomes; also helps bond
amino acids together to make polypeptides
(proteins)!

The goal of the 3 types of RNA is to work

together to make proteins using the DNA’s
instructions!

Multiple Choice

Brings the amino acids to the ribosome

• mRNA

• tRNA

• rRNA

• DNA

TRANSLATION

Transfer RNA (tRNA)= helps transfer amino acids to the corresponding mRNA

codons (tRNA is always complementary to the mRNA strand)

mRNA codons: U G C A A U C G G

tRNA anticodons: A C G U U A G C C

tRNA bases are referred to as “anti-codons” because they are

complementary to mRNA codons.

mRNA strand (codons) U G C A A U C G G

tRNA strand (anti-codons) A C G U U A G C C

TRANSLATION

tRNA transfers amino acids

to the ribosome. The amino
acids are attached to the
tRNA via a specialized
enzyme called tRNA
synthetase.

Analogy: tRNA is a librarian; mRNA
codons are the book codes; amino acids
are the books. tRNA reads the mRNA and
fetches the appropriate amino acid.

Example)

If the mRNA codon is

CUU, that would
translate to the amino
acid leucine.

The tRNA molecule that

will deliver leucine to the
ribosome has the
anticodon GAA.

Once the amino acid is delivered, the tRNA releases
itself from the ribosome, and leaves to find another
amino acid to add to the growing polypeptide chain.

ANTICODON

LEUCINE

Multiple Choice

What best explains the interaction between tRNA and mRNA during translation?

• anticodons on the mRNA line up with complementary codons on the tRNA

• anticodons on the tRNA line up with complementary codons on the mRNA

• tRNA attach amino acids to the complementary mRNA sequence

• mRNA attach amino acids to the complementary tRNA sequence

Multiple Choice

What does tRNA "transfer"?

• amino acids

• nucleic acids

• nucleotides

• AUG

DNA Template Strand: A C G T T A G C C

mRNA strand: U G C A A U C G G

Codons?

1)

UGC

2)

AAU

3)

CGG

Which three amino
acids do these
mRNA codons
code for?

1.
2.
3.

LABEL THE FOLLOWING:

MRNA, TRNA, RIBOSOME, PEPTIDE (PROTEIN) CHAIN,

AMINO ACID

START AND STOP SIGNALS

Proteins are made up of a very specific sequence of amino

acids.

DNA contains “start” and “stop” codons so that the cell knows

where to start decoding proteins and where to stop.

The start codon= AUG (codes for the amino acid methionine)

Stop codons = UAA, UAG, UGA

Multiple Choice

What process is going on in this photo? 

• Transcription 

• Translation 

• Replication 

• All the above 

Multiple Choice

The process to go from mRNA to a protein is called ____

• transcription

• rRNA

• replication

• translation

Multiple Choice

What is the location in the cell for transcription?

• nucleus

• cytoplasm

• ribosome

• mitochondria

Multiple Choice

The main function of tRNA is to

• Carry a message that, when translated, forms proteins

• Form a portion of ribosomes

• String together complementary RNA and DNA strands

• Carry amino acids to the ribosomes where they are joined to form proteins

Multiple Choice

The main function of mRNA is to

• Copy DNA in the nucleus and carries the information to the ribosomes

• Bring amino acids from the cytoplasm to the ribosomes

• String together complementary RNA and DNA strands

• Form a portion of ribosomes

PUTTIN’ IT ALL TOGETHER

DNA codes for proteins
Proteins are made during

protein synthesis

Transcription occurs in the

nucleus. The final product
of transcription is an
mRNA strand.

Translation occurs on the

ribosomes in the
cytoplasm. The final
product of translation is a
protein.

Overview

● When a particular protein is needed, the cell must make the

protein through the process of transcription and translation.

● DNA molecules (which contain the code) do not leave the

nucleus of the cell.

● Protein synthesis occurs on ribosomes located outside of the

nucleus.

● Therefore, the code must be carried from the nucleus to the

cytoplasm.

● RNA plays an important role in protein synthesis but it can also

have other functions in the cell.

○ mRNA is essential to the process of transcription, tRNA is

essential to the process of translation, and rRNA makes up
the ribosomes in which translation takes place.

Overview

●

Transcription is the process by which a portion of the molecule of
DNA is copied into a complementary strand of RNA. The process of
transcription takes place as follows:

○

An enzyme attaches to the DNA molecule at the gene of interest.

○

The two strands of DNA separate at that location.

○

Complementary RNA nucleotides bond to the nitrogenous bases on
one of the separated DNA strands.

○

The chain of RNA nucleotides forms a single-stranded molecule of
RNA by using the DNA strand as a template.

○

When a stop codon is reached, the RNA strand separates from the
DNA molecule, leaves the nucleus and goes through the nuclear
membrane into the cytoplasm.

○

The two DNA strands rejoin.

Overview

●

Translation is the process by which the genetic message, carried by the
mRNA, is used to assemble a protein.

○

The mRNA attaches to a ribosome, which contains proteins and ribosomal
RNA (rRNA). The function of ribosomes is to assemble proteins according
to the genetic message.

○

Each three-base nucleotide sequence on the mRNA is called a codon. Each
codon specifies a particular amino acid that will be used to build the
protein molecule. For example, if the DNA sequence was GAC, then the
RNA sequence becomes CUG (transcription) and the amino acid that is
coded is Leucine (translation).

○

Another type of RNA, transfer RNA (tRNA), brings amino acids to the
ribosome in the order specified by the codon sequence on the mRNA. At
one end of each tRNA is the anticodon, a region that consists of three
nucleotide bases that are complementary to the codon of mRNA. The
other end of the tRNA molecule binds to the specific amino acid that is
determined by the mRNA codon.

Overview

● The translation process takes place as follows:

○

The anticodon of the tRNA, with its attached amino acid, pairs
to the codon of the mRNA, which is attached to a ribosome.

○

When a second tRNA with its specific amino acid pairs to the
next codon in sequence, the attached amino acid breaks from
the first tRNA and is bonded to the amino acid of the second
tRNA.

○

The ribosome forms a peptide bond between the amino acids,
and an amino acid chain begins to form.

○

The empty tRNA moves off and picks up another matching
amino acid from the cytoplasm in the cell.

○

This sequence is repeated until the ribosome reaches a stop
codon on the mRNA, which signals the end of protein synthesis.