Gene Expression

Question 1

Define genome

Answer 1

The complete set of genes or genetic material present in a cell or an organism

Question 2

Define gene

Answer 2

regions of DNA that are made up of nucleotides

Question 3

Differentiate between introns and exons.

Answer 3

An intron is a segment of DNA or RNA that does not code for proteins and interrupts the sequence of genes (non-coding)

An exon is a segment of DNA or RNA containing information coding for a protein or peptide sequence.

Question 4

Explain the 3 steps of transcription and state where the process takes place

Answer 4

Takes place in the nucleus.

1. Initiation - proteins bind to DNA sequences close to the promoter region of a gene. RNA polymerase attatches to the promotor unwinding and unzipping the DNA molecule by breaking the hydrogen bonds between the two strands.
2. Elongation - RNA polymerase covers approximately 30 base pirs forming a transcription bubble. RNA polymerase moves along the DNA molecule creating a complementary mRNA strand. 5’ - 3’.
3. Termination - Transcription ends when RNA polymerase reaches the termination site of a gene. This region contains a stop triplet code. The mRNA is sent out of the nucleus to the ribosomes to be used for protein synthesis and the DNA is reconnected.

Question 5

Describe the 3 steps in Translation

Answer 5

1. Initiation - a small ribosomal subunit attaches to the 5’ end of an mRNA strand. A tRNA molecule with the anticodon UAC then brings the methionine to the mRNA. The tRNA then joins to the mRNA start codon. The binding of both ribosomal subunits causes the formation of three special sites for tRNA to bind: the aminoacyl site (A site), the peptidyl site (T site), and the exit site (E site).
2. Elongation - Following the attachment of methionine, another tRNA with a complementary anticodon on the mRNA attaches and adds its specific amino acid to the growing polypeptide chain. The ribosome then releases the tRNA and moves further along the mRNA strand. At each codon, a new tRNA binds and adds another amino acid. This process repeats until the polypeptide chain is finished.
3. Termination - Attachment of amino acids continues until a stop codon is reached. The polypeptide chain is then released from the ribosome into the cytoplasm or the endoplasmic reticulum.

Question 6

What is the purpose of gene expression?

Answer 6

to synthesise a functional gene product that the that the process can be regulated and is used by all known life

Question 7

What are the 3 factors that regulate the phenotypic expression of genes?

Answer 7

• Transcription and translation
• through the products of other genes
• via environmental exposure

Question 8

What does differential gene expression regulate?

Answer 8

cell differentiation for tissue formation and morphology

Question 9

Provide one example of a transcription factor gene that regulates morphology and one example for cell differentiation

Answer 9

HOX transcription factor family and sex-determining region Y

Question 10

What is the role of a HOX gene?

Answer 10

To specify positional identity in the embryo rather than the development of any specific structure. These positional values are interpreted differently in different embryos to influence how the cells in a region develop. They determine general body plan, such as the number of body segments of an animal, the number and placement of appendages and the animal head-tail directionality.

Question 11

How do mutations in genes and chromosomes result in errors in DNA replication?

Answer 11

Frameshift and point mutations can occur if errors occur

Question 12

How do mutations in genes and chromosomes result in errors in cell division?

Answer 12

non-disjunction - the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

Question 13

What mutagens can cause mutations in genes and chromosomes?

Answer 13

UV radiation, ionising radiation, heat and chemical

Question 14

What is non-disjunction?

Answer 14

the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

Question 15

What is aneuploidy?

Answer 15

the condition of having an abnormal number of chromosomes in a haploid set. e.g. downs syndrome

Question 16

How does non-disjunction lead to aneuploidy?

Answer 16

Non-disjunction is a genetic event during cell division where chromosomes fail to separate correctly. This results in one cell receiving an extra chromosome while another cell lacks that chromosome. When these cells divide, the subsequent daughter cells inherit an abnormal number of chromosomes, leading to aneuploidy—a condition characterized by an abnormal chromosome count, such as trisomy (an extra chromosome) or monosomy (a missing chromosome).

Question 17

Define Polygenic inheritance

Answer 17

Polygenic inheritance refers to the mode of inheritance where a particular trait is influenced by the combined effects of multiple genes, rather than being controlled by a single gene. These genes may be located on different chromosomes and each contribute a small amount to the expression of the trait. As a result, polygenic traits often display a continuous range of variation and are influenced by environmental factors, making their inheritance more complex than traits determined by a single gene.