Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Gene Expression

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Biology

Eukaryotes (multicellular organisms) possess cells that contain a complete set of chromosomes (unless mutations occur). Cell genes in these chromosomes code for proteins and give commands on what cells will have to do in their life cycle. Gene expression will act as an "on" and "off" switch for proteins and their amounts that a specific cell will have to make. The cell will be controlled to make more if needed and less if not.

What is gene expression?

Gene expression is the translation and transcription of genetic information. It determines which genes are translated and transcribed and how many. The DNA of each of these cells includes genes needed to make all the proteins required. However, not every gene is expressed. Due to the expression of different genetic codes in cells, they become specialised and carry out specific functions.

All the DNA in eukaryotic organisms contain less than 10% of the genes that code for proteins. The majority of the DNA is non-coding, essential for controlling gene activity. Non-coding DNA contains structural DNA, which helps maintain the structure of chromosomes in eukaryotes.

Functional RNA does not code for proteins but plays an essential role in synthesising proteins, e.g. tRNA. The synthesis of particular proteins due to the expression of different genes determines an organism's phenotype, i.e. the physical characteristics of an organism. However, the base sequence of the DNA determines the organism's genotype.

The function of gene expression

Genes encode proteins, and proteins dictate cell function. Therefore, the combination of genes active in a particular cell determines the identity of a cell and its tasks. The activation of genes is called gene expression. It is tightly regulated at several points, from the initial stage of transcription to splicing and the translation of the proteins and the changes to the final protein structure. These processes are controlled to monitor and maintain cell types with required characteristics.

Not all parts of a gene code for the amino acid sequence of a protein molecule. The gene is composed of coding sections called exons and non-coding sections called introns. After the gene is transcribed into RNA, the introns are spliced out of the RNA molecule. Then the exons reattached to each other, forming a single mature mRNA molecule. This is splicing. The inclusion of introns or disruption of the order of exons in the mature mRNA molecule would produce a dysfunctional protein.

Splicing: Introns are removed, and exons are spliced together. Without this step, proteins would be non-functional.

Introns: Non-coding sections of the RNA transcript.

Exons: Coding sections of the RNA transcript.

Therefore, gene expression uses information from genes to synthesise proteins or RNA molecules. The synthesis of proteins involves RNA in the processes of transcription and translation. You can read more about these vital processes in the Transcriptional Regulation and Translation Regulation explanations.

RNA in gene expression

Now, let's revise the structure and function of RNA, to understand its vital role in gene expression better.

RNA differs from DNA in the following ways:

Table 1. The main differences between RNA and DNA.

RNADNA
Single strand.Double helix (two strands).
Ribonucleic acid in the nucleotide.Deoxyribonucleic acid (one less oxygen-containing hydroxyl group) in the nucleotide. Deoxyribonucleic acid makes DNA more stable than RNA.
Base pairing: Cytosine bonds with Guanine (C-T) and Adenine bonds with Uracil (A-U).Cytosine bonds with Guanine (C-G), and Adenine bonds with Thymine (A-T).

Three forms of RNA are involved in the translation and transcription of genes in a cell. These three forms are:

  • Messenger RNA (mRNA) carries a copy of the gene to be expressed from the nucleus to the ribosome, where it can be translated.
  • Transfer RNA (tRNA) consists of only one strand of RNA, which folds because of base pairing. Each tRNA molecule carries its specific amino acid to the ribosome.
  • Ribosomal RNA (rRNA), rRNA, together with proteins, forms ribosomes.

Genes

DNA in genes contains instructions, consisting of non-coding instructions (sequences of DNA) and code for RNA or proteins. Coding regions of a gene are called exons, and non-coding ones are called introns. The DNA code consists of nitrogenous bases: adenine, cytosine, guanine, and thymine. Different base pair combinations create different amino acids and therefore produce various proteins.

A codon (three bases) codes for one amino acid. There are 20 amino acids and four bases (64 codons possible). Amino acids are specified by more than one codon, referred to as redundancy. Not all mutations will change the amino acid sequence of proteins; some mutations might still code for the same amino acid.

Codon: A specific DNA or RNA sequence corresponding to a particular amino acid.

Epigenetics: the study of how behaviour and environment contribute to the changes in your genes and affect the way they work.

Cells that can express every one of their genes are stem cells. Stem cells can become any cell in the body because they can produce all the proteins needed to create a specific structure and carry out particular tasks. You can find more detail on this subject in the stem cells article.

The development of stem cells into particular body cells can occur due to the factors involved in transcription and translation. This regulation of protein synthesis means that different genes are expressed, and various proteins are made, enabling the development of stem cells into different body cells. Epigenetic control of genes determines whether a gene is expressed via altering how proteins and enzymes involved in transcription can transcribe the DNA. Uncontrolled cell growth can create mutations, which may develop into tumours. Tumours can be harmful and non-harmful, but you'll find more information about tumours in the article on Epigenetics.

Protein Synthesis/Stage 1 of Gene Expression

DNA helicase unwinds the DNA double helix, and the hydrogen bonds between base pairs are broken. RNA polymerase creates a complementary template strand. The result of this process is a molecule called pre-mRNA.

This pre-mRNA molecule is 'spliced', where introns are removed, and the remaining exons are re-joined. The molecule is referred to as mRNA after spicing.

  1. During translation, the mRNA leaves the nucleus. The template strand travels to the ribosome to which it attaches.
  2. Transfer RNA (tRNA) brings free amino acids from the cytoplasm to the mRNA in the ribosome. The codon on mRNA forms complementary base pairs with the anticodon of the tRNA molecule allowing the tRNA to specify the amino acid. The specific amino acid is bound to the other end of the tRNA molecules.
  3. tRNA molecules are attached to the mRNA via the ribosome, which moves along the mRNA strand. As the ribosome covers two codons, two tRNA molecules are attached, and a peptide bond forms between them.
  4. The amino acids form a polypeptide chain, and as each amino acid is attached, they separate from the tRNA. This allows the tRNA molecule to return to the cytoplasm and bring another amino acid.
  5. The protein (polypeptide chain) formed can be changed by combining polypeptide chains or adding a phosphate or carbohydrate group.

Every protein has a unique shape designed to carry out a specific function. The primary structure, i.e. the sequence of amino acids, allows every protein to have a unique shape as there is nearly an unlimited number of possible amino acid combinations. The secondary structure of proteins can take one of two shapes: the alpha-helix or beta-pleated sheets.

The tertiary structure integrates alpha-helices and beta-pleated sheets, forming a unique three-dimensional structure.

If you need more information about the tertiary structure, you can find it in the article on protein structure.

The quaternary structure of proteins consists of multiple polypeptide chains. The quaternary structure might contain prosthetic groups. These are non-protein groups that become integrated into the chains. This forms what is called a conjugated protein, e.g., haemoglobin. The primary structure dictates the secondary, tertiary and quaternary structures.

The disturbance of the primary structure completely changes the protein's function, highlighting the importance of the amino acid sequence.

Gene expression [+] the different levels of protein structure [+] Study Smarter

Figure 5. Protein structure. Source: wikipedia.org

Regulation of gene expression

Many of the genes in humans code for factors that regulate the transcription and translation of different genes. These factors control which genes are expressed and used to make proteins and control which genes are not. The sequences that do not create a protein have the essential function of regulating the expression of other genes.

One such factor involved in gene regulation is an activator. Proteins must bind to the promoter region at the start of the DNA to be transcribed. Activator proteins such as RNA polymerase bind to the promoter legion and activate transcription.

Regulatory elements can have general or specific effects. These effects are described in the article on regulating transcription and translation. The regulation of translation involves RNA interference, which causes mRNA not to be translated into proteins. RNA interference uses siRNA (small interfering RNA in mammals) and miRNA (micro interfering RNA in mammals and plants). Refer to the article on regulation of translation for more detail.

Gene Expression - Key takeaways

  • Regulation of gene expression patterns in eukaryotic cells is a complex process that occurs at various levels, from elements within the DNA of modifications to complete proteins.
  • Not every piece of DNA holds instructions to make a protein; some sequences exist to regulate the expression of other genes.
  • Genes are made up of introns and exons. Introns are removed from the final mRNA. Promoters and enhancers are regulatory elements that do not code for proteins but regulate the expression of genes.
  • RNA is essential in the synthesis of proteins as it allows a template to be made (mRNA) of the original strand. It also allows specific amino acids to be brought together to form the polypeptide chain (tRNA).
  • Haemoglobin is a protein with a quaternary structure called a conjugated protein. The disturbance of its amino acid sequence would cause a completely different protein to be formed, and it would not carry out the function of haemoglobin.

Gene Expression

Gene expression affects the activation of genes in a cell. It affects whether all the genes in a cell are expressed and controls which genes are switched off (not expressed). This dictates the proteins produced and influences what functions the cell carries out.

Epigenetic changes do not affect the base sequence of DNA; however, they affect whether genes are expressed or how much some genes are expressed.

Many factors influence the expression of genes, such as intracellular structures (molecules within the cell). Transcription factors affect which genes are expressed, and epigenetic changes influence how much gene expression occurs or whether some genes are expressed or not.

A heat map is how gene expression data is illustrated. The data is displayed in a grid in which there are rows and columns. Each column represents a sample, and each row represents a gene. The colors and their intensity varies according to changes in gene expression.

The levels of the gene product (proteins produced) are quantified and displayed in a heat mat to measure the gene expression levels. From the data, the level of gene expression can be interpreted. Western blotting (Southern blotting involves identification of DNA, whereas western blotting identifies proteins) can be used to quantify gene products as well as the ELISA test.

Final Gene Expression Quiz

Question

What is the general appearance of a tumour cell?

Show answer

Answer

  • They have a larger and darker nucleus compared to other cells. 

  • They may have more than one nucleus.

  • They have an irregular shape.

  • They don't produce all proteins needed to function correctly

  • They have different antigens on their surface compared to normal cells.

  • They don't respond to the body's regulating processes.

  • They divide by mitosis more frequently than normal cells.

Show question

Question

Metastasis definition

Show answer

Answer

When a piece of tumour cell breaks off and spreads to another part of the body.

Show question

Question

What are cohort studies?

Show answer

Answer

Cohort studies follow a group over time to see who develops diseases and who doesn't. Exposures to risk factors are recorded over time.

Show question

Question

What factors affect the risk of developing cancer?

Show answer

Answer

  • Diet - There is strong evidence that suggests that a good diet rich in fruit, veg and fibre reduces the risk of getting cancer.
  • Obesity - Linked to diet, being overweight also increases the risk of cancer. 
  • Exercise - People who are more physically active are at a lower risk than those who do little or no exercise.
  • Sunlight - The more ultraviolet light someone is exposed to, the more at risk they are.
  • Smoking - Both smokers and those who breathe in tobacco passively are at increased risk of cancer.

Show question

Question

Correlation definition

Show answer

Answer

A correlation is the statistical measure of the relationship between two variables. It is best demonstrated in variables with a linear relationship between each other.

Show question

Question

What are cohort studies?


Show answer

Answer

Cohort studies follow a group over time to see who develops diseases and who doesn't. Exposures to risk factors are recorded over time.

Show question

Question

Benign definition

Show answer

Answer

A mass of cells that doesn’t invade neighbouring tissue or metastasise

Show question

Question

How does a malignant tumour form?

Show answer

Answer

  • Malignant cells develop, divide and invade normal tissues.

  • Some of the cells detach and spread through the blood and lymph vessels.

  • The malignant cells can squeeze through the capillary wall.

  • They then divide, producing a secondary tumour in a different location to the original tumour.

Show question

Question

What is a disadvantage of cohort studies?


Show answer

Answer

Cohort studies are very time consuming and expensive in comparison to case studies. This is because it takes people a long time to develop diseases.

Show question

Question

Malignant definition


Show answer

Answer

Tumours that spread through the body and cause cancer.

Show question

Question

What causes cancers to arise?


Show answer

Answer

Uncontrolled cell division

Show question

Question

How are mutations kept under control?


Show answer

Answer

  1. Picked up by various regulatory functions in the cell cycle
  2. Early cell death (apoptosis)
  3. Being destroyed by the bodies immune system

Show question

Question

What are cohort studies?


Show answer

Answer

Cohort studies follow a group over time to see who develops diseases and who doesn't. Exposures to risk factors are recorded over time.

Show question

Question

Compare and contrast benign and malignant tumours.


Show answer

Answer

Both benign and malignant tumours can grow large however benign tumours grow slowly, and have more localised effects whereas malignant tumours grow rapidly and have systemic effects. Benign tumours can usually be removed by surgery alone whereas malignant tumours often require radiotherapy or chemotherapy as well. They are also more likely to be life-threatening than benign tumours and have a high rate of recurrence. Benign tumours are often surrounded by a capsule and don't metastasise whereas malignant tumours don't have a capsule and do metastasise.

Show question

Question

What is the correlation coefficient used for?


Show answer

Answer

To determine whether too variables correlate. 

Show question

Question

What are case studies?

Show answer

Answer

A group of people who have the disease to be studied are compared with a group of individuals who do not have the disease.

Show question

Question

What is the aim of preventative medicine?

Show answer

Answer

To stop an illness before it starts and takes a holistic approach by focusing on the many factors that play a role in health. This includes maintaining a healthy lifestyle.

Show question

Question

How could epigenetic changes affect humans?

Show answer

Answer

They could cause disease, either by inhibiting or activating a gene.

Show question

Question

What effect do different genes in a cell being expressed have?


Show answer

Answer

Different proteins are made and these proteins modify the cell.

Show question

Question

Describe the process of RNA interference.


Show answer

Answer

RNA molecules inhibit gene expression, by destroying mRNA so that it cannot be translated.

Show question

Question

Why does the structure and function of different cells vary in an organism?


Show answer

Answer

Not all the genes in a cell are expressed.

Show question

Question

Describe RNA interference using siRNA.


Show answer

Answer

mRNA leaves the nucleus once it has been transcribed and enters the cytoplasm.

  • Double-stranded RNA cut using enzymes.

  • Each small section is called siRNA.

  • siRNA has a specific base sequence that is complementary to the target mRNA.

  • One strand of the siRNA binds to a protein (RISC) which then acts as an enzyme. 

  • The siRNA can now bind to the mRNA molecule by complementary base pairing.

  • The mRNAs phosphodiester bonds are hydrolysed.

  • The mRNA can no longer be used in translation and is broken down by the nuclease enzyme. 

Show question

Question

What is gene expression?

Show answer

Answer

The activation of genes in a cell. Not all the genes in a cell are expressed, and many are switched off. This process is tightly regulated at several stages.

Show question

Question

When does gene expression occur? 


Show answer

Answer

The gene expression process occurs during transcription and translation and involves RNA.

Show question

Question

What is 'splicing'?


Show answer

Answer

RNA splicing is the process during which non-coding regions of DNA (introns) sequences are removed.

Show question

Question

What are regulatory elements? 


Show answer

Answer

Regulatory elements regulate the transcription and translation of genes. This means they affect which genes are expressed and determine the proteins produced.

Show question

Question

Discuss why every cell does not express all of its genes.


Show answer

Answer

Every cell does not express every single gene as valuable space is saved. This is because less DNA is uncoiled by DNA helicase. Valuable energy is saved as less protein synthesis occurs.

Show question

Question

How do cells 'decide' which genes to turn on?

Show answer

Answer

A cell's gene expression is determined by information from both inside and outside the cell. 

  • Inside - eg proteins it inherited from its mother cell, whether it's DNA is damaged and how much ATP it has.

  • Outside - chemical signals from other cells, mechanical signals from the extracellular matrix, and nutrient levels.

Show question

Question

How does gene expression occur in prokaryotic organisms?

Show answer

Answer

Prokaryotes are single-celled organisms that have no nucleus, so their DNA floats freely in the cytoplasm. To synthesize a protein, transcription and translation occur almost simultaneously. When a resulting protein is no longer needed, transcription stops. Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.

Show question

Question

What are non-coding regions of DNA called?


Show answer

Answer

Introns.

Show question

Question

What is the process of removing non-coding regions of DNA called, and when does this occur?


Show answer

Answer

Splicing. It occurs before the RNA migrates to the cytoplasm.

Show question

Question

What are the types of RNA?


Show answer

Answer

mRNA, tRNA, rRNA.

Show question

Question

What happens if the gene expression process goes wrong?

Show answer

Answer

Malfunctions in this process are detrimental to the cell and can lead to the development of many diseases including cancer.

Show question

Question

Where can totipotent stem cells be found?

Show answer

Answer

In the first few cell divisions of a zygote.

Show question

Question

Where can totipotent stem cells be found?

Show answer

Answer

In the first few cell divisions of a zygote.

Show question

Question

What are pluripotent stem cells?

Show answer

Answer

Stem cells found in embryos can specialise into any body cell but lose the ability to develop into cells that make up the placenta.

Show question

Question

Why and how do stem cells become specialised?


Show answer

Answer

They become specialised because during their development they transcribe and translate only specific parts of their DNA.

Show question

Question

How are embryonic stem cells obtained?


Show answer

Answer

They can be obtained from embryos after the first few divisions of the zygote. Embryos are created in a lab environment using IVF. After the first few cell divisions, the stem cells are removed and the embryo is destroyed.

Show question

Question

What type of stem cells are embryonic stem cells?


Show answer

Answer

They are pluripotent stem cells

Show question

Question

How are induced pluripotent stem cells (iPS cells) obtained?


Show answer

Answer

IPS cells are created by inserting transcription factors into already specialised cells to give them pluripotency.

Show question

Question

Give an example of stem cell therapy and explain how this is carried out.


Show answer

Answer

Leukaemia can be treated via stem cells from bone marrow. Bone marrow transplants are used to remove the faulty bone marrow in leukaemia patients that produce abnormal blood cells. The transplanted stem cells from a donor divide and specialise into healthy blood cells.

Show question

Question

What is the difference between cell differentiation and cell specialisation? 


Show answer

Answer

Specialisation means the cell begins to adopt specific sizes, shapes etc which enable it to carry out its function more efficiently. Differentiation means the cell starts to become a different and specific type of cell.

Show question

Question

How do stem cells start to differentiate?


Show answer

Answer

 Both stem cells and differentiated cells possess the same genetic material. Stem cells differentiate into specialised cells by expressing specific genes and keeping the rest of the genome turned off. 

Show question

Question

Do stem cell treatments/transplants involve a lot of risks?


Show answer

Answer

Stem cell treatments involve some risk as with any surgical treatment. However, stem therapies involve quite a lot of discomfort for both the patient and donor. The level of discomfort involved also differs depending on where the stem cells are being obtained from.

Show question

Question

Why are iPS cells favoured over embryonic stem cell use? 


Show answer

Answer

This is because the use of embryonic stem cells is surrounded by ethical issues as embryos are destroyed which could have become a fetus. Also, iPS cells are made from the patient's own stem cells so will not trigger the same immune response as using embryonic stem cells would.

Show question

Question

What are three adaptations of erythrocytes?

Show answer

Answer

  • Loss of their nucleus and mitochondria to create more space for haemoglobin, which is the main oxygen-carrying protein in erythrocytes.

  • An increase in the concentration of haemoglobin in the cell increases to ensure maximum oxygen-carrying capacity.

  • Adoption of a specific cytoskeleton that gives the erythrocytes a biconcave structure granting them a larger surface area for gas exchange and increased flexibility to travel through narrow blood vessels.

Show question

Question

What are the sources of stem cells?

Show answer

Answer

Adult stem cells, embryonic stem cells, umbilical cord blood stem cells, placental stem cells, and induced pluripotent stem cells.

Show question

Question

What is a stem cell?

Show answer

Answer

A cell that can specialise to develop into specific cells in the body.

Show question

Question

What is a transcription factor?

Show answer

Answer

A protein molecule that controls the transcription of genes.

Show question

Question

What is transcription?

Show answer

Answer

When a gene is copied from DNA into RNA via RNA polymerase 

Show question

60%

of the users don't pass the Gene Expression quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.