Genetics

What three components make up the central dogma of molecular biology?

The central dogma describes the flow of genetic information from DNA to RNA to protein.

In the central dogma, what is the role of DNA?

DNA acts as the cell's genetic 'blueprint', organised into genes that encode specific traits.

According to the central dogma, RNA is described as a temporary 'photocopy' of a gene made via what process?

RNA is made via transcription.

What is the term for sequences of DNA that encode a specific characteristic and function as the basic units of inheritance?

Genes.

A gene is composed of three key sections: the promoter, the coding sequence, and the _.

terminator

What is the function of the promoter region of a gene?

The promoter is the site to which RNA polymerase binds to initiate transcription.

Which part of a gene is the region of DNA that is transcribed into RNA?

The coding sequence.

What is the function of the terminator sequence in a gene?

The terminator sequence signals RNA polymerase to stop transcription.

Which type of RNA is the transcript copy of a DNA instruction that encodes the protein sequence?

Messenger RNA (mRNA).

What is the role of transfer RNA (tRNA) in protein synthesis?

Transfer RNA (tRNA) carries amino acids to the mRNA transcript for assembly at the ribosome.

Which type of RNA provides the catalytic activity for combining amino acids together during translation?

Ribosomal RNA (rRNA).

Define transcription in the context of gene expression.

Transcription is the process where a DNA sequence (gene) is copied into a complementary RNA sequence by RNA polymerase.

During transcription, what does RNA polymerase do after binding to the promoter?

It separates the double-stranded DNA of the coding sequence by breaking the hydrogen bonds between base pairs.

In transcription, how are free RNA nucleotides joined together to form an RNA transcript?

RNA polymerase joins them together with covalent bonds along the sugar-phosphate backbone.

What ensures that the RNA transcript is a correct and reliable copy of the genetic instructions?

The system of complementary base pairing between DNA and RNA nucleotides.

In RNA, adenine pairs with _ via two hydrogen bonds.

uracil

How many hydrogen bonds form between guanine and cytosine during transcription?

Three hydrogen bonds.

What are transcription factors?

Proteins produced by regulatory genes that coordinate the expression of other genes by mediating or impeding RNA polymerase binding.

What is the function of activator proteins in gene expression?

Activator proteins bind to enhancer sites to increase transcription rates.

What is the function of repressor proteins in gene expression?

Repressor proteins bind to silencer sites to decrease transcription rates.

What is the term for the study of changes in organisms resulting from variations in gene expression levels?

Epigenetics.

Term: Genome

Definition: The totality of DNA sequences (both genes and non-coding DNA) within a cell or organism.

Term: Proteome

Definition: The totality of proteins expressed within a cell or organism at a particular time.

Why do different cell types in a multicellular organism differ in morphology and function despite having the same genome?

Different genes are activated in different tissues, leading to the production of different proteins (a different proteome).

Define translation in the context of protein synthesis.

Translation is the process where genetic information encoded in mRNA is translated into a sequence of amino acids to form a polypeptide.

During translation, the ribosome reads the mRNA sequence in triplets of bases called _.

codons

What molecule brings the correct amino acid to the ribosome based on the mRNA codon?

Transfer RNA (tRNA).

How does a tRNA molecule recognise the correct codon on an mRNA sequence?

It uses a complementary triplet of bases called an anticodon.

What type of bond is formed between adjacent amino acids during translation?

Peptide bonds.

What is the function of the small subunit of a ribosome?

The small subunit binds to the messenger RNA (mRNA).

What is found on the large subunit of a ribosome?

The large subunit contains binding sites for two tRNA molecules.

What specific mRNA codon initiates translation and establishes the reading frame?

The start codon, AUG.

What feature of the genetic code means that almost every living organism uses the same code?

Universality.

The characteristic of the genetic code where some codons code for the same amino acid is known as _.

degeneracy

In sickle cell anaemia, a mutation changes the mRNA codon from GAG to what?

The codon changes from GAG to GUG.

What amino acid substitution is caused by the GAG to GUG mutation in sickle cell anaemia?

Glutamic acid is replaced by valine (Glu → Val).

What is a gene mutation?

A change in the nucleotide sequence of a section of DNA encoding for a specific trait.

New versions of a gene that arise from mutations are called _.

alleles

Which type of mutation, somatic or germline, can be passed on to offspring?

Germline mutations (in gametes) can be passed on.

Name one cause of gene mutations that occurs during DNA replication.

Proofreading errors by DNA polymerase that are not corrected.

Term: Mutagen

Definition: An agent that induces a permanent change to the genetic material of an organism, increasing the mutation frequency.

Name a physical mutagen mentioned in the source material.

Radiation, such as X-rays or UV light.

Name a chemical mutagen mentioned in the source material.

Reactive oxygen species, certain metals (e.g., arsenic), or alkylating agents from grilling meat.

Name a biological mutagen mentioned in the source material.

Certain viruses (like HPV) or bacteria (like H. pylori).

What is a point mutation?

A change to a single base within the DNA code, such as a base substitution.

A _ mutation occurs when a change in the DNA does not alter the amino acid sequence due to codon degeneracy.

silent

What type of point mutation results in a single amino acid change in the polypeptide chain?

A missense mutation.

What is the consequence of a nonsense mutation?

It creates a premature STOP codon, truncating the polypeptide.

What is a frameshift mutation?

A mutation involving an insertion or deletion of a nucleotide that alters the reading frame of the DNA code.

Which type of mutation involves changes to large segments of a chromosome?

Block mutations.

A block mutation where part of a chromosome is copied, resulting in duplicate sections, is called a _.

duplication

What is a translocation mutation?

A block mutation where a chromosome sequence is moved to a new location, potentially on a different chromosome.

In which direction does RNA polymerase synthesise new RNA strands during transcription?

In a 5' → 3' direction.

In which direction do ribosomes read the mRNA sequence during translation?

In a 5' → 3' direction.

What are introns?

Introns are non-coding sequences found within protein-encoding genes in eukaryotes.

In eukaryotic RNA processing, what is added to the 5'-end of the transcript to prevent degradation?

A methyl group cap (capping).

What is the purpose of adding a poly-A tail to the 3'-end of an RNA transcript in eukaryotes?

To improve the stability of the transcript (polyadenylation).

What is the process of removing introns from a pre-mRNA transcript called?

Splicing.

What are the coding sequences of a eukaryotic gene that are fused together after splicing?

Exons.

What is alternative splicing?

A process where exons can be selectively removed along with introns, allowing for the formation of different polypeptides from a single gene.

How can alternative splicing lead to a proteome that is larger than the genome?

Multiple protein variants can be produced from a single genetic sequence.

During the elongation phase of translation, a new tRNA molecule binds to which site on the ribosome?

The A site.

After transferring its amino acid, the deacylated tRNA moves to the _ site before being released from the ribosome.

E site

What molecule binds to the stop codon to cause the dissociation of the ribosome and polypeptide from the mRNA?

A release factor.

What part of an amino acid is variable and gives each of the 20 amino acids its distinct chemical properties?

The side chain (R group).

What level of protein structure is defined by the order of amino acids in a polypeptide chain?

Primary structure.

Secondary protein structures, such as α-helices and β-pleated sheets, are formed by what type of bonding?

Hydrogen bonding between the amine and carboxyl groups of non-adjacent amino acids.

The complex 3D folding of a single polypeptide chain is referred to as its _ structure.

tertiary

What type of interactions form the tertiary structure of a protein?

Interactions between variable R groups, including hydrogen bonds, ionic bonds, and disulphide bonds.

What level of protein structure involves the interaction of multiple polypeptide chains to form a single active protein?

Quaternary structure.

_ proteins are typically long, narrow, insoluble, and have structural roles.

Fibrous

_ proteins are typically round, spherical, soluble, and have functional roles.

Globular

Where does the modification of proteins destined for secretion, like insulin, primarily occur?

In the rough endoplasmic reticulum (ER) and the Golgi apparatus.

Proteins destined for secretion are synthesised by ribosomes that become bound to the _.

endoplasmic reticulum

What is the function of proteasomes within a cell?

Proteasomes are complexes that degrade misfolded or no longer needed polypeptides, recycling their amino acids.

How are proteins targeted for degradation by a proteasome?

They are tagged with a short polypeptide called ubiquitin.

While the _ is identical in all cells of an organism, the transcriptome and proteome can vary.

genome

What is a transcriptome?

All the genetic instructions that have been actively transcribed to RNA within a cell at a particular time.

Regulating the longevity of mRNA transcripts is a form of _ control of gene expression.

translational

What is epigenesis?

The specific development of an organism from an undifferentiated zygote via differential gene expression.

What is the effect of DNA methylation at a gene's promoter region?

It impedes the activity of RNA polymerase, reducing transcriptional activity and switching the gene 'off'.

Adding a methyl group to histone tails makes DNA more coiled, turning it into condensed _, which is not accessible for transcription.

heterochromatin

What is the term for loosely packed chromatin that is accessible to transcription machinery?

Euchromatin.

Why are studies of monozygotic twins useful for understanding epigenetics?

Because they have identical genomes, differences in their traits and DNA methylation patterns can be attributed to environmental factors.

What happens to most epigenetic tags in gametes during their development?

They are erased (reprogrammed) to return the gamete to a blank genetic slate for the new embryo.

What are imprinted genes?

Genes that do not undergo epigenetic reprogramming during gamete production and retain their epigenetic tags, allowing these changes to be passed to offspring.