Learning Objectives
1. Explain the main differences between DNA, RNA, & proteins.
DNA contains the genetic blueprint in a double helix structure, using deoxyribose sugar and bases adenine, thymine, cytosine, and guanine. RNA is single-stranded, uses ribose sugar, and replaces thymine with uracil. Proteins are complex molecules formed by amino acids, functioning as the machinery and structural elements of cells.
2. Identify the locations of DNA & the various RNAs in the cell.
DNA is primarily located in the cell nucleus, while RNA (mRNA, tRNA, rRNA) is found both in the nucleus and cytoplasm. mRNA carries the genetic code from DNA to the cytoplasm, rRNA is a component of ribosomes, and tRNA brings amino acids during protein synthesis.
3. Explain the relationship between DNA, a gene, nucleotides, amino acids, and proteins.
DNA, composed of nucleotides, contains genes, which are sequences encoding proteins. Each gene, through transcription, produces mRNA, which is translated into a sequence of amino acids, forming proteins.
4. List the parts of a gene & describe the functions of each.
A gene typically includes a promoter, coding sequence, and terminator. The promoter regulates gene expression, the coding sequence is transcribed into mRNA, and the terminator signals the end of transcription.
5. Describe how the process of transcription works.
Transcription involves copying a gene's DNA sequence to make an mRNA molecule. RNA polymerase binds to the DNA at the promoter region, separates the DNA strands, and synthesizes a complementary RNA strand from the DNA template.
6. Transcribe a DNA sequence into an mRNA sequence.
To transcribe a DNA sequence into mRNA, substitute thymine (T) with uracil (U) and transcribe the complementary bases (A->U, T->A, G->C, C->G). For example, DNA 5’-ATGC-3’ becomes mRNA 3’-UACG-5’.
7. Describe the structures that are added to & removed from an mRNA transcript before it leaves the nucleus.
Before mRNA leaves the nucleus, a 5’ cap and a poly-A tail are added for stability and regulation, and introns (non-coding regions) are removed while exons (coding regions) are spliced together.
8. Explain what alternative splicing is & why it is important for cells.
Alternative splicing is the process where different combinations of exons are joined to produce multiple mRNA variants from a single gene, increasing protein diversity and functional complexity in cells.
9. Identify the organelles that perform the process of translation.
Translation occurs in the ribosomes, which can be found either free in the cytoplasm or bound to the endoplasmic reticulum.
10. Describe how the process of translation works.
Translation is the process of converting mRNA into a protein. Ribosomes read mRNA codons, tRNA brings corresponding amino acids, and these are linked together to form a polypeptide chain, creating a protein.
11. Explain what a codon is.
A codon is a sequence of three nucleotides in mRNA that specifies a particular amino acid or a start/stop signal in protein synthesis.
12. Use the Genetic Code Table to translate an mRNA sequence.
Using the Genetic Code Table, each mRNA codon can be matched to its corresponding amino acid. For example, mRNA codons AUG, UUU, and GGG translate to Methionine, Phenylalanine, and Glycine, respectively.
13. Explain what differential gene expression is & why it is used in cells.
Differential gene expression is the process by which cells express different genes to perform different functions, allowing for cell specialization and the complex organization of multicellular organisms.
14. Describe the role of transcription factors in differential gene expression.
Transcription factors are proteins that bind to specific DNA sequences, controlling the transcription of genetic information from DNA to mRNA. They play a key role in regulating gene expression and thus contribute to cell differentiation.
15. Explain what occurs in a point mutation & a frameshift mutation.
A point mutation involves a single nucleotide change. A frameshift mutation occurs when nucleotides are inserted or deleted from the sequence, altering the reading frame of the gene.
16. Describe the effects of silent mutations, missense mutations, and nonsense mutations on translation.
Silent mutations don't change the amino acid sequence. Missense mutations change one amino acid, possibly altering protein function. Nonsense mutations introduce a premature stop codon, potentially truncating the protein.
17. Identify the major sources of mutations in a cell.
Mutations can arise from errors during DNA replication, exposure to mutagens (like UV light, chemicals), and spontaneous chemical changes in DNA.
18. Describe how a cell responds to mutations.
Cells respond to mutations with DNA repair mechanisms. If repair is not possible, cells may undergo apoptosis to prevent the propagation of harmful mutations.