Genetics recap 4/10/22

Question 1

How is a protein coded for?

Answer 1

Three nucleotides create a triplet, a triplet creates an amino acid, two or more amino acids create a peptide, a chain of amino acids is a polypeptide, and several polypeptides joined together is a protein.

Question 2

What is the structure of DNA?

Answer 2

DNA (deoxyribonucleic acid) has a phosphate backbone. Four nucleotides A (adenine), T (thymine), C (cytosine), and G (guanine). A and T are joined by two hydrogen bonds, C and G are joined by three hydrogen bonds.

Question 3

Where is DNA material stored?

Answer 3

The nucleus of a cell contains the genome inside 23 pairs of chromosomes. Chromosomes contain long strands of DNA which are tightly packed around histone proteins. DNA contains sections called genes and genes contain the instructions to make proteins.

Question 4

How does transcription work?

Answer 4

RNA polymerase attaches to the 3’ side of a DNA strand at the start of a gene (promotor/start codon). RNA polymerase separates the DNA and uses free nucleotides to build an RNA strand 5’ to 3’. The RNA has the same information as the non-template (coding) DNA strand, U (uracil) is used instead of T. A CAP (modified G) is before a coding region and a poly-A tail is at the end of one and formed using A nucleotides, both these protect the mRNA from degrading. The produces the pre-mRNA strand ready to be spliced.

Question 5

How does translation work?

Answer 5

The mature mRNA strand leaves the nucleus into the cytoplasm and the ribosome attaches. Ribosome reads the mRNA from 5’ to 3’ in triplet. The transfer RNA brings the amino acids that is coded for by the triplet and this creates the polypeptide strand. The polypeptides join together to form a protein.

Question 6

What is a polyadenylation signal?

Answer 6

When a sequence called a polyadenylation signal shows up in an RNA molecule during transcription, an enzyme chops the RNA in two at that site. Another enzyme adds about 100- 200 adenine (A) nucleotides to the cut end, forming a poly-A tail.

Question 7

What is an exon?

Answer 7

An exon contains all the coding information for proteins in the genes.

Question 8

What is an intron?

Answer 8

An intron contains no coding information and can disrupt transcription and translation if not removed.

Question 9

How does RNA splicing work?

Answer 9

Introns need to be removed and contain marker sequences at their start and end which are recognised by the small RNA and direct the spliceosome to the intron. Once removed the spliceosome joins the exons together. Only exons code for proteins so introns need to be removed otherwise a wrong protein could be produced. The spliceosome contains a protein and RNA complex. This produces a mature RNA ready to be translated.

Question 10

What is alternative splicing?

Answer 10

There are several different exons in a single gene. Therefore, depending on which exons are spliced or kept different proteins can be coded for.

Question 11

What is the structure of proteins?

Answer 11

Primary - the linear sequence coded by DNA
Secondary - the way the linear sequence folds, this can be alpha helix or beta sheets
Tertiary - the 3D shape of a polypeptide
Quaternary - the 3D shape of several polypeptides that make the whole protein

Question 12

How many amino acids are there?

Answer 12

There are 20 amino acids. They contain oxygen, carbon dioxide, nitrogen, hydrogen, and some sulphur.

Question 13

What is a missense mutation?

Answer 13

A missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. It is a type of nonsynonymous substitution.

Question 14

What is a nonsense mutation?

Answer 14

A nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA. This means the sequence is incomplete and usually produces a non-functional protein product.

Question 15

What is an RNA processing mutation?

Answer 15

An RNA processing mutation is a point mutation in the DNA that can affect how transcription, splicing, and translation occur. For example, a mutation in the promotor or termination region could affect DNA polymerase from attaching or detaching. A mutation at the start or end of an intron could affect the spliceosome from cutting out the correct sections and could mean incorrect parts of the gene are translated. Depending on the mutation, where it is, and at what point it occur in RNA processing, this can change the severity of the impact that the mutation has on protein production and therefore the person.

Question 16

What is a splice site mutation?

Answer 16

A splice site mutation can be a mutation that inserts, deletes or changes a number of nucleotides in the specific site at which splicing takes place during the processing of precursor messenger RNA into mature messenger RNA which can affect what DNA is cut or incorrectly kept.

Question 17

What is a long range regulatory mutation?

Answer 17

Regulatory factors can either enhance or repress the expression of a gene. For example, an activator can help an RNA polymerase binds to the promotor region, a repressor can block a promotor region so that an RNA polymerase can’t bind and therefore the gene is repressed, or a binding site. DNA methylation causes the segment to be repressed and reduces transcription whereas histone acetylation loosens a chromatin structure which would increase transcription. Any mutation in genes that code for these enhancer or repressors could change the production of a protein.

Question 18

What is a nonsynonymous mutation?

Answer 18

This is a mutation that causes an alteration in the amino acid sequence and typically causes an issue.

Question 19

What is a synonymous mutation?

Answer 19

This is a mutation that doesn’t change the amino acid sequence and therefore is a silent mutation as it doesn’t cause any issues.

Question 20

What is a frameshift mutation?

Answer 20

A frameshift mutation is a mutation in which a number of nucleotides deleted or inserted into a protein coding sequence is not divisible by three, thereby causing an alteration in the reading frame of the entire coding sequence downstream of the mutation.

Question 21

What is a small indels mutation?

Answer 21

An indels mutation is an insertion or deletion of a nucleotide and result in a change of 1 to 50 nucleotides.

Question 22

What is a deletion mutation?

Answer 22

A deletion mutation changes the DNA sequence by removing at least one nucleotide in a gene. Small deletions remove one or a few nucleotides within a gene, while larger deletions can remove an entire gene or several neighbouring genes.

Question 23

What is an insertion mutation?

Answer 23

An insertion mutation is the addition of one or more nucleotide base pairs into a DNA sequence.

Question 24

What is an inversion mutation?

Answer 24

An inversion mutation occurs when a chromosome breaks, and the resulting piece of DNA is reversed and re-inserted into the chromosome. Genetic material may or may not be lost as a result of the chromosome break.

Question 25

What is a fusion mutation?

Answer 25

A fusion mutation can occur when two different genes join, and this can result in proteins being produced that cause cancer.

Question 26

What is a duplication mutation?

Answer 26

A duplication mutation is when one or more copies of a DNA segment which can be as small as a few bases or as large as a major chromosomal region is produced.

Question 27

What does UTR mean?

Answer 27

UTR means the untranslated region. These can be either 5’ UTR or 3’ UTR depending on where the untranslated region is. The 5’ or 3’ UTR region before the coding gene can determine the life of the mRNA made, therefore, mutations in the UTR can change the mRNA lifespan.

Question 28

What is a dynamic mutation?

Answer 28

A dynamic mutation is an inherited mutation where the mutation is repeated a set number of times before the symptoms of the disease will present. This means that onset ages and time for the disease to develop can be different from the predecessor. For example, Huntington’s disease requires a certain number of repeats of the HTT gene in order for the disease to present.

Question 29

What is a loss of function mutation?

Answer 29

Loss of function mutations involve a reduction or complete loss of function of the gene product.

Question 30

What is a gain of function mutation?

Answer 30

Gain of function mutations can be beneficial but can also result in a non-beneficial gene product, excess production
of the gene product or a functionally altered gene product.

Question 31

What is aneuploidy?

Answer 31

This is when there are extra or missing chromosome. However, if an entire set is extra or missing this is not aneuploid.

Question 32

What is an euploid?

Answer 32

This is when you have the correct number of chromosomes.

Question 33

What is monosomy?

Answer 33

When an organism has only one copy of a chromosome that should be present in two copies (2n-1).

Question 34

What is trisomy?

Answer 34

When an organism has a third copy of a chromosome that should be present in two copies (2n+1).

Question 35

What is a translocation mutation?

Answer 35

A translocation mutation occurs when a piece of one chromosome gets attached to another chromosome. These can either be a reciprocal translocation which involves two chromosomes swapping segments or a non-reciprocal translocation which means that a chunk of one chromosome moves to another.

Question 36

What is nondisjunction?

Answer 36

Failure of homologous chromosomes or sister chromatids to separate properly during cell division.

Question 37

How is chromatin regulated and affected by mutations?

Answer 37

Genes within highly packed heterochromatin are usually not expressed. Chromatin-modifying enzymes provide initial control of gene expression by making a region of DNA either more or less able to bind the transcription machinery.

Remodelling complexes can facilitate the binding of acetyltransferase which lead to acetylation (opens up the chromatin structure, thereby promoting the initiation of transcription) or deacetylase which reverses this. Complexes such as methyltransferase can also be used to cause methylation (condenses chromatin and reduce transcription) or demethylase which reserves this.

Inactive (packed) chromatin is methylated on the tails of H3 at specific lysines and on cysteine of specific
CpG sites. Active (open) chromatin is acetylated on the tails of H3 and H4.

Question 38

What is epigenetics?

Answer 38

Epigenetics is the study of how cells control gene activity without changing the DNA sequence. Epigenetic changes are modifications to DNA that regulate whether genes are turned on or off. Within the complete set of DNA in a cell (genome), all of the modifications that regulate the activity (expression) of the genes is known as the epigenome.

Environmental influences, such as a person’s diet and exposure to pollutants, can impact the epigenome and can be inherited.

Two common forms of regulation are DNA methylation (turns off or silences the gene) and histone modification (adding/removal of acetyl or methyl groups that turns off or silences a gene).

Epigenetics errors can lead to a lot of genetic disorders and cancer.

Question 39

How does non-coding RNA (IncRNA) regulate gene expression and affect when mutated?

Answer 39

The expression of a considerable number of lncRNAs is regulated and some have roles in different mechanisms of gene regulation. Several lncRNAs control the expression of nearby genes by affecting their transcription, and also affect other facets of chromatin biology, such as DNA replication or the response to DNA damage and repair. Other lncRNAs function away from their loci; their functions can be of a structural and/or regulatory nature and involve different stages of mRNA life, including splicing, turnover and translation, as well as signalling pathways.

Any alteration/mutation of their expression is inherent to numerous diseases. The specific expression patterns of these functional lncRNAs have the potential of being used as optimal disease biomarkers, and strategies are under development for their therapeutic targeting.

Question 40

What is mosaicism?

Answer 40

This condition occurs in multicellular organisms in which a single organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized egg.