Author: Biology Junction Team

Meta: Need to learn how protein synthesis works? We’ve got your complete guide to the process on our protein synthesis worksheet, including the difference between DNA and RNA, important misconceptions about mutations, and an explanation of the central dogma of biology. Plus, get practice exercises and quiz questions. 

 

What is Protein Synthesis?

 

Protein synthesis is the construction of proteins within living cells. The process consists of two parts; transcription and translation.

Proteins are an important organic compound that exists in every living organism. They are an essential part of the majority of cell functions. Specific proteins are needed for particular functions. Proteins are made up of long chains of amino acids which can be arranged in either a linear pattern or can be folded to form a more complex structure.

Proteins can be complex in structure and so are filtered into four categories – primary secondary, tertiary and quaternary.

Protein synthesis is a biological procedure which living cells perform to create new proteins. When studied in detail, the chemical synthesis of proteins process is extremely complex. The process begins with the production of new and different amino acids, some of which are collected from food sources.

The process requires ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and a specific set of enzymes. All the different types of ribonucleic acids are needed for protein synthesis to work effectively. These are messenger ribonucleic acid (mRNA), transfer ribonucleic acid (tRNA), and ribosomal ribonucleic acid (rRNA).

 

 

Protein Synthesis: Definition, Examples, and Practice

Let’s check out a couple of important definitions to better understand protein synthesis.

Most protein synthesis worksheets will require a working understanding of the following definitions:

Central Dogma of Biology

A polypeptide encoded in a gene is expressed in a directional relationship called the central dogma of biology. It recognizes that information moves from the DNA to the RNA to the protein.

DNA

Deoxyribonucleic acid (otherwise known as DNA), is the carrier of genetic info found in almost every found living organism to date. It is present in the nucleus of cells and is self-replicating, meaning it’s integral to protein synthesis.

RNA

RNA is ribonucleic acid, and it’s present in every living cell discovered to date. It is a messenger and vitally involved in translating genetic code from DNA to the ribosomes so that amino acids can be created.

There are three kinds of RNA: messenger RNA (mRNA) transfers the genetic code from the DNA in the nucleus out to the ribosomes in the cytoplasm. Ribosomal RNA (rRNA) provides the structure for the ribosomes. Finally, transfer RNA (tRNA) works during translation to bring the amino acids to the ribosome so that a polypeptide (an amino acid chain) can be built.

Transcription

Transcription is the stage of manufacturing in which the DNA gene sequence is copied so that an RNA molecule can be made. We’ll explain more shortly.

Translation

The second stage of protein synthesis is translation. At this point in the process, a mRNA (messenger RNA) molecule is “read” and the information is used by the ribosome to build a polypeptide.

Polypeptide

A polypeptide is a chain made up of amino acids.

Codon

Three nucleotides form a codon. This codon is then used to create amino acids.

RNA vs. DNA

It’s tempting to confuse RNA with DNA, but they’re very different, and it’s important to understand these differences. They are both made up of nucleotides, which are the basic units of nucleic acids (like DNA and RNA). These nucleotides contain a phosphate group, a nitrogenous base, and a 5-carbon sugar ribose.

Instead of DNA’s ribose, however, RNA uses deoxyribose, a different kind of sugar. Also, RNA is most often a single strand, while DNA is famously double-stranded. Finally, DNA contains thymine, while RNA uses uracil instead.

Chromosomes

DNA is found by the meter inside even minuscule cells. During replication, the masses of coiled DNA called chromatin (shaped thanks to proteins called histones) organize into what are called chromosomes.

Different types of cells (eukaryotes) have chromosomes in varying amounts. Humans, as you probably know, have 46 chromosomes, while dogs, for example, have 78.

Transcription and Translation

To best understand your protein synthesis worksheet, let’s cover the complete protein synthesis process. It starts with transcription. Special enzymes in the nucleus arrive to gently pull apart the DNA code needed, and RNA begins to transcribe or rewrite the genetic material.

During translation, the mRNA connects with the ribosome and its information is decoded again so that the correct sequence of amino acids will connect to form a polypeptide. It’s important to note here that the ribosome doesn’t make protein nor does it make amino acids. It simply instructs already-made amino acids to form the correct sequence.

The amino acids’ sequence determines its protein’s shape, function, and properties and it can do so thanks to the RNA’s four bases (all of which are nucleotides): adenine (A), cytosine (C), guanine (G), and uracil (U). A codon, as we explained earlier, is a combination of three of these bases in a specific order: UUC, for example.

Some codons tell the ribosome to start or stop (UAA, UAG, and UGA indicate stop) and the rest indicate specific amino acids.

Understanding the Codon Table

Image Source: sabal.uscb.edu

The heart of protein synthesis (and what you’ll most likely see on a protein synthesis worksheet) is the codon table. It helps us work through translation to understand the amino acids the mRNA is prescribing. For example, if you want to know what the codon CAA translates to, you’ll use the first letter of the codon (C) to locate the corresponding row on the left side of the chart.

Next, use the second letter of the codon (A) to identify the corresponding column on the top of the chart. The box indicated includes four codons that began with C and A; if you’d like, you can simply identify your codon there, or you can use the right side of the chart to identify the corresponding order of the third letter in the codon (A).

Either way, the single amino acid for CAA is Gln (glutamine).

Mutations

Mutations sound scary, but don’t worry–we’re not talking about superheroes with latent power and plans for world domination. Instead, we’re talking about what happens when there’s a mistake in the transcription or translation process.

Mutations come in three forms: silent, missense, and nonsense. A mutation that is silent means that the amino acid will not be impacted during translation. Missense mutations mean that the single amino acid has been changed and a nonsense mutation ends prematurely.

How are Mutations Caused?

There are several different reasons a mutation may occur. If at least one base is added to a DNA sequence, this is referred to as an insertion. A deletion, however, occurs when at least one base has been removed from the DNA sequence.

Similarly, when a change is made to the codons so that the reading frame of the sequence is changed, the resulting mutation is called a frameshift mutation. For example, a mRNA codon that reads AUG-AUA-CGG-AAU might experience an insertion of a T in the DNA sequence.

This frameshift mutation leads to a new codon: AUG-UAC-GGA-AU.

If we utilize the codon chart, we find that the polypeptide mutates from Met-Ile-Arg-Asn to Met-Tyr-Gly.

Common Misconceptions About Mutations

Something important to note is that sometimes the DNA sequence experiences an insertion or deletion of three nucleotides in a row. This doesn’t cause a frameshift mutation. Instead, it will just impact whether or not the deleted or inserted amino acids are added or not.

This can cause a dramatic change in the outcome of the polypeptide.

Another common misconception is that a mutation is always dramatic. While this is sometimes the case, mutations are common and provide the genetic variation we so appreciate in life. Many mutations have little to no impact on life, and some mutations even create good changes.

It’s a very limited number of mutations that survive to be problematic.

 

What Exactly Are Genes?

 

A gene is a short section of DNA that acts as an instruction manual for our bodies. DNA is found inside almost every cell in the body.

Genes contain the instructions that tell cells to create new proteins via protein synthesis. Every gene carries certain instructions which make up who you are such as eye color, height, and hair color. Genes come in many different types and versions for each feature. For example, one variant of a gene may contain instructions for blue eyes whereas another contains instructions for brown eyes. Genes are so small that there are around 20,000 inside each cell in the body. The entire sequence of your genes is named the genome.

 

How Do Genes Work?

 

Genes are responsible for telling each of your cells what to do and when to do it. They do this by making proteins. Why are proteins important? Well, our bodies are made up of proteins. Around 50% of a cell is some form of protein. Proteins are also responsible for many bodily functions such as digestion, immunity, circulation, motion, and communication between cells. These are made possible by the estimated 100,000 different proteins that are produced in the body.

Genes within your DNA don’t make proteins directly. Instead, enzymes read and copy the DNA code. The section of DNA that is to be copied gets unzipped by an enzyme which then uses that segment of DNA as a template to build a single-stranded molecule of ribonucleic acid. This ribonucleic acid then leaves the nucleus of the cell and enters the cytoplasm where ribosomes then translate the code to create the specific protein.

In certain genes, not all of the DNA sequence is used to make a protein. The section of DNA that is non-coding is known as introns. The coding sections of DNA are called exons.

 

The Structure of DNA

 

DNA is made up of pairs of nucleotides on a phosphate and sugar backbone. There are four different nucleotides: thymine, cytosine, guanine, and adenine. Each of the types of nucleotides only pairs with one other type. Hydrogen bonds connect to those nucleotide pairs. The sugar and phosphate backbone, along with the nucleotide pairs form a ladder-like structure that twists to form the double helix structure of DNA. Each side of this ladder shape is known as a strand of DNA.

 

Nucleotides consist of a base, a phosphate group, and five carbon atoms. Each of the different types of nucleotide has a base with a different structure, however, all the bases contain nitrogen. The four bases can be split into two groups. These are pyrimidine bases and purine bases. Pyrimidine bases are small and have one six-atom ring. Purine bases are larger and are made up of a six-atom ring plus a five-atom ring which are joined by two shared atoms. Thymine and cytosine are pyrimidine bases and adenine and guanine are purine bases.

 

Pyrimidine bases bond to purine bases because the shapes of these bases allow hydrogen bonds to form between them. The base pairing rules states that guanine pairs only with cytosine and adenine pairs only with thymine. This rule is known as complementary base pairing. Three hydrogen bonds form between a guanine and cytosine pair whereas only two hydrogen bonds form between an adenine and thymine base pair.

 

Protein Synthesis Worksheet Practice

It’s helpful to utilize practice protein synthesis worksheets. To help you, here’s a list of questions–and their answers–that you’re likely to find on tests, worksheets, and protein synthesis projects:

1. During translation, which RNA carries amino acids to the ribosome? (transfer RNA or tRNA)
2. Is DNA made with uracil or thymine? (thymine)
3. In which part of the cell does transcription happen? (in the nucleus)
4. Which RNA carries the genetic code to the ribosomes from the DNA? (messenger RNA or mRNA)
5. What is the central dogma of biology? (DNA → RNA → protein)
6. What are the building blocks of proteins? (amino acids)
7. What are the three causes of mutations? (insertion, deletion, and frameshift)
8. What is a codon? (three nucleotides)
9. What are the three differences between DNA and RNA? (RNA uses deoxyribose instead of ribose, is single-stranded instead of double-stranded, and contains uracil instead of thymine)
10. In what phase is tRNA molecules used? (translation)
11. Does protein synthesis build protein? (no; protein synthesis builds amino acids)
12. What are polypeptides? (chains of amino acids)
13. What do codons do? (indicate the specific amino acid and in what order, and indicate when to stop and start the amino acid chain)
14. Which leaves the nucleus: DNA or RNA? (RNA)
15. What are the three kinds of mutations? (silent, missense, and nonsense)
16. Which codons indicate stop? (refer to the codon chart for the answer; UAA, UAG, and UGA)
17. What does chromatin organize into during replication? (chromosomes)

Practice with the Codon Chart

Another great way to increase your knowledge of protein synthesis and better prepare for protein synthesis worksheets is to practice with the codon chart. You can find the solutions in parenthesis after the example:

1. CUU-CGU-AAU-UGG-AAG (leu-arg-asn-trp-lys)
2. ACU-ACA-AGU-UGC-UUU (thr-thr-ser-cys-phe)
3. AAC-AAG-GUC-GUC-AGG (asn-lys-val-ile-arg)

Protein synthesis is a complex, highly tuned process that enables life to flourish. Understanding it, from the DNA to the RNA to the amino acids, gives us a better appreciation for life itself. Use our protein synthesis worksheet practice questions to help you learn the ins and outs of protein synthesis and remember the informaion.