1Define transcription.
Synthesis of an mRNA strand from a DNA template strand, called the antisense strand.
2List the roles of RNA polymerases in the process of transcription.
The enzyme RNA polymerase transcribes DNA to RNA
3State the complementary base pairing utilized in transcription.
During transcription, complementary base pairing rules match DNA template bases to new RNA nucleotides: Adenine (A) pairs with Uracil (U), Cytosine (C) pairs with Guanine (G), and Guanine (G) pairs with Cytosine (C). The key difference from DNA pairing (where A pairs with Thymine) is that Uracil (U) replaces Thymine (T) in RNA
4Distinguish between the sense and antisense strands of DNA.
The sense (coding) strand of DNA has the same sequence as the mRNA (with U instead of T) and contains the protein's code, while the antisense (template) strand is complementary to the sense strand and serves as the direct template for building mRNA during transcription.
The sense strand runs 5' to 3', while the antisense strand runs 3' to 5' (antiparallel), and it's the antisense strand that gets read to make mRNA, resulting in an mRNA that matches the sense strand's sequenc
5Outline how stability of the information stored in DNA is maintained.
The stability of information in DNA is maintained by its double-stranded structure with complementary base pairing. This allows accurate semi-conservative replication and enables repair mechanisms to correct errors, preserving genetic information.
6Define gene expression.
Gene expression is the process by which information in a gene is used to produce a functional product such as a polypeptide or RNA.
7Outline the major steps of gene expression.
Gene expression involves transcription followed by translation.
8State that the pattern of gene expression is how cells differentiate for specific functions.
Different patterns of gene expression cause cells to differentiate into specialised types. Gene expression is regulated by transcription factors and can be influenced by environmental factors.
9Outline the role of transcription in regulating gene expression.
Gene expression can be regulated at transcription because transcription factors control whether RNA polymerase binds to DNA and how much mRNA is produced
10Define translation.
Translation is the process by which ribosomes use the sequence of codons in mRNA to assemble a polypeptide, During translation, ribosomes read mRNA in triplets called codons, each of which codes for a specific amino acid.
11State the location of translation in cells.
on ribosomes in the cytoplasm (including ribosomes on rough ER).
12Outline the roles of mRNA, ribosomes and tRNA in translation.
mRNA carries the genetic code from DNA to the ribosome.
Ribosomes read mRNA codons and catalyse polypeptide synthesis.
tRNA carries specific amino acids and has an anticodon complementary to the mRNA codon.
13Describe the structures of mRNA and tRNA.
mRNA is a single-stranded molecule made of ribonucleotides with a sugar-phosphate backbone and bases A, U, C and G arranged in codons.
tRNA is a folded RNA molecule with regions of complementary base pairing, an anticodon loop, and an amino acid attachment site at the 3′ end (CCA).
14Describe the structure of the ribosomes, including the small and large subunits and the names and roles of the tRNA binding sites.
Ribosomes are composed of a small and large subunit made of ribosomal RNA and proteins. The small subunit binds to mRNA, while the large subunit catalyses peptide bond formation. Ribosomes have three tRNA binding sites: the A site where aminoacyl-tRNA enters, the P site where the polypeptide chain is held and peptide bonds form, and the E site where tRNA leaves after releasing its amino acid.
15State the complementary base pairing utilized in translation.
During translation, complementary base pairing occurs between the codon on mRNA and the anticodon on tRNA.
16Define codon and anticodon.
A codon is a triplet of bases on mRNA that codes for an amino acid.
An anticodon is a complementary triplet of bases on tRNA.
17Describe the formation of hydrogen bonds between codon and anticodon.
Hydrogen bonds form between complementary bases of the codon on mRNA and the anticodon on tRNA, allowing the correct tRNA to bind during translation.
18Explain the reason that a sequence of three nucleotides is required to code for the 20 amino acids commonly utilized by organisms.
There are four different bases in RNA. A code of two bases would give only 16 combinations, which is insufficient to code for 20 amino acids. A triplet code allows 64 possible codons, which is enough.
19Define codon, degenerate and universal as related to the genetic code.
Codon: a triplet of bases on mRNA that codes for an amino acid or stop signal.
Degenerate: more than one codon can code for the same amino acid.
Universal: the genetic code is the same in almost all organisms, suggesting common ancestry.
20Use a genetic code table to determine the amino acid sequence coded for by a given DNA or RNA sequence.
To determine an amino acid sequence, the DNA template is first transcribed into complementary mRNA. The mRNA codons are then read using a genetic code table to identify the corresponding amino acids.
See slide 23
21Outline the process of translation elongation, including codon recognition, bond formation and translocation.
During elongation, a tRNA with a complementary anticodon binds to the codon at the A site. A peptide bond forms between the amino acid in the P site and the amino acid in the A site. The ribosome then moves along the mRNA, shifting the tRNAs from A to P to E site. The empty tRNA leaves and the polypeptide chain lengthens.
22Define gene mutation.
A gene mutation is a permanent change in the nucleotide base sequence of a gene.
23State the cause of sickle cell anemia, including the differences in the HbA and HbS alleles.
Sickle cell anemia is caused by a base substitution mutation in the β-globin gene producing haemoglobin S instead of haemoglobin A. it is autosomal recessive inheritance
24State the difference in RNA sequences in the transcription of the HbA and HbS alleles.
HbA has the mRNA codon GAG whereas HbS has GUG due to a base substitution mutation.
25State the difference in amino acid sequences in the translation of the HbA and HbS alleles.
The mutation causes valine to replace glutamic acid at the sixth position of the β-globin polypeptide.
26Outline the consequences of the HbS mutation on the structure and function of the hemoglobin protein.
The mutation changes the primary structure of haemoglobin by substituting valine for glutamic acid. This creates hydrophobic interactions causing haemoglobin molecules to stick together and form fibres. Red blood cells become sickle-shaped, reducing oxygen transport and blocking capillaries.
27Discuss the symptoms of sickle cell disease.
Sickle cell disease causes anaemia due to reduced oxygen transport.
Blockage of capillaries leads to pain crises and tissue damage.
Patients may experience
fatigue
increased infection risk
organ complications.