Gene Expression: Unit 4, Topic 1

Question 1

Define a genome

Answer 1

All the genetic material in the chromosomes of an organism, including its genes and DNA sequences.

Question 2

Define gene

Answer 2

• region/s of DNA that are made up of nucleotides; the molecular unit of heredity
• coded proteins determine every characteristic of every organism

Question 3

What is Coding DNA (EXONS)

Answer 3

• small part of DNA used as a template for mRNA synthesis and this for polypeptide synthesis.
• also known as a gene (transcribed into mRNA and then translated into polypeptides.

AKA -> exon: the small portion of a gene that codes for amino acids.

Question 4

What is Non-Coding DNA?

Answer 4

• the DNA sequences within the genome that are not found within mRNA-coding exons
• do not code for polypeptides (may be transcribed into RNA but is not translated into proteins)
• most non-coding SNA lies between genes on the chromosomes and has no known function.

Examples of non-coding DNA:
- intros: found within genes
- telomere: the end of a chromosome (protection during replication)
- centromere: links the pair of sister chromatids
- non-coding RNA genes (tRNA and rRNA) - not translated into the protein.

Question 5

Explain Protein in relation to Protein synthesis.

Answer 5

• protein consists of one or more polypeptide chains
• these polypeptide chains have molecules that consist of amino acids.
• These amino acids are made from 3 adjacent nucleotide bases that code for one amino acid called a codon.

DNA -> (transcription) -> RNA -> (translation) -> protein

DNA has protein synthesis intructions -> message is carried from DNA to ribosomes using RNA -> ribosome in the cytoplasm synthesis proteins.

Question 6

what is protein synthesis?

Answer 6

Protein synthesis is the process in which cells build proteins by transcribing DNA into mRNA in the nucleus, then translating the mRNA into a specific sequence of amino acids at the ribosome.

The two stages needed is transcription and translation.

Question 7

What is transcription? What stages does it undergo?

Answer 7

• the reading of DNA and using the information to create complementary strands of mRNA.

Stages of Transcription:
1. DNA unwinds and unzips (DNA helicase), exposing the nucleotide bases of both DNA strands.
2. The RNA polymerase then joins complicated RNA nucleotides, resulting in mRNA.
3. Once the mRNA molecule has peeled off, the DNA zips up again and twists itself back into a double helix.
4. Following synthesis, the strand is considered pre-mRNA; before leaving the nucleus, it undergoes splicing -> some introns are removed and exons joined back together.
5. leaves the nucleus and travels through the cytoplasm.

Question 8

What is Translation? What stages does it undergo?

Answer 8

• The joining of amino acids in specific order to form a polypeptide

Stages of Translation:
1. mRNA moves into the cytoplasm, and a ribosome will attach to it (ribosome: site of translation)
2. when the ribosome reaches the starting codon (AUG), the ribosome will start assembling amino acids to form a polypeptide chain (assisted by the tRNA)
3. tRNA transfers amino acids from the cytoplasm to the ribosome so it can be added to the polypeptide chain
- tRNA has specific anticodons (a sequence of three nucleotide cases that pair with complementary bases on mRNA)
- the complementary anticodons are attracted to the codons on the mRNA and form weak hydrogen bonds.
4. Between 3 anticodons, a peptide bond is formed. Then the first tRNA detaches from its anticodon, leaving the amino acid attached behind, attaching to the next tRNA.
5. The ribosome continues down the mRNA strand and repeats these steps until a stop codon is reached. A polypeptide chain (protein) has been formed and is released into the cytoplasm

Question 9

What is a gene expression? What is gene regulation?

Answer 9

• Gene being transcribed into mRNA and translated into a polypeptide or functional RNA
• allows a cell to respond to its changing environment - acts as an on/off switch to control when proteins are made and how much.
• controls over how fast genes are transcribed and translated.

Gene regulation
- processes within cells that enable a gene to be expressed just in particular cells and at specific times and rates

In Eukaryotic cells - the default state of a gene expression is “off” except for the housekeeping genes (genes that are continually expressed at some level to maintain cell function).

Question 10

What is the differential gene expression? What is a Homeobox gene?

Answer 10

• the activation of different cell genes with a specific purpose.
• determines the gene that the individuals need
• outcome is regulating cell differentiation for tissue formation and morphology

Homeobox genes (HOX) - code for proteins (regulatory proteins) that regulate body formation and patterning in the developing embryo - act as transcription factors.
- once HOX gene is activated -> the product is a protein that binds to DNA to activate gene expression.

Question 11

What are HOX genes?

Answer 11

• encode transcription factors proteins
• turned by a cascade of regulatory genes