Biology chapter 12/15.1-

1. DNA and RNA differ in several aspects. In terms of function, DNA stores genetic information, while RNA plays various roles in protein synthesis and gene regulation. The sugar in DNA is deoxyribose, whereas RNA contains ribose. Regarding bases, DNA has adenine, thymine, cytosine, and guanine, while RNA has adenine, uracil (instead of thymine), cytosine, and guanine. DNA is typically double-stranded, forming a double helix, while RNA is usually single-stranded.

2. The primary structure of a polypeptide is determined by the sequence of amino acids, which is dictated by the nucleotide sequence of the corresponding gene in DNA. This sequence is transcribed into mRNA, which is then translated into a polypeptide chain.

3. Gene expression is the process by which information from a gene is used to synthesize a functional gene product, often a protein. The two major processes involved are transcription, where the DNA sequence is copied into mRNA, and translation, where the mRNA is used as a template to assemble amino acids into a polypeptide.

4. In prokaryotes, transcription and translation occur in the cytoplasm simultaneously, as there is no nucleus. In eukaryotes, transcription occurs in the nucleus, and translation occurs in the cytoplasm. An extra step in eukaryotes is RNA processing, which includes capping, polyadenylation, and splicing.

5. The structural gene contains the coding sequence for a protein. The promoter is a regulatory sequence that initiates transcription. The terminator signals the end of transcription. Regulatory sequences can enhance or inhibit transcription, and the transcribed region is the part of the gene that is copied into mRNA.

6. During transcription, initiation involves the binding of RNA polymerase to the promoter region, aided by transcription factors in eukaryotes or sigma factors in prokaryotes. Elongation is the process where RNA polymerase synthesizes the mRNA strand by adding nucleotides complementary to the DNA template. Termination occurs when RNA polymerase reaches a terminator sequence, causing it to release the newly formed mRNA.

7. DNA is read in the 3' to 5' direction, while mRNA is synthesized in the 5' to 3' direction. The cell knows where to start making mRNA due to the presence of a promoter region. Only one strand of DNA, known as the template strand, is used to make mRNA, while the other strand is referred to as the coding strand.

8. The corresponding mRNA for the transcribed region 3' ATATACGGA 5' would be 5' UAUACGCUU 3'.

9. RNA processing in eukaryotes includes three steps: adding a 5' cap, which protects the mRNA and assists in ribosome binding; adding a poly-A tail at the 3' end, which stabilizes the mRNA and aids in export from the nucleus; and splicing, which involves removing introns (non-coding regions) and joining exons (coding regions) together to form a continuous coding sequence.

10. Genetic engineering is the manipulation of an organism's genome using biotechnology. The universality of the genetic code allows genes from one organism to be expressed in another. However, a human gene cannot be directly introduced into a bacterial cell to produce the normal human protein due to differences in post-translational modifications and the presence of introns in eukaryotic genes that bacteria cannot process.

11. During translation, mRNA serves as the template for protein synthesis. tRNA (transfer RNA) carries specific amino acids to the ribosome, where ribosomes facilitate the assembly of amino acids into polypeptides. Start codons signal the beginning of translation, while stop codons signal the end. Release factors help terminate the process by prompting the release of the completed polypeptide.

12.The significance of the reading frame during translation is crucial because it determines how the sequence of nucleotides in mRNA is divided into codons, which are then translated into amino acids. The reading frame is determined by the starting point of translation, specifically the first codon that is read by the ribosome, which is usually the start codon AUG. If a mutation occurs that alters the reading frame, it is known as a frameshift mutation. This type of mutation can result from the addition or deletion of nucleotides that are not in multiples of three, leading to a completely different translation of the downstream amino acids.

13.Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids, while anticodons are complementary sequences of three nucleotides in tRNA that pair with the codons during translation. For example, if the codon is AUG, the anticodon would be UAC. The anticodon sequence is essential for the correct incorporation of amino acids into the growing polypeptide chain.

14.The three major steps during translation are initiation, elongation, and termination.

1. Initiation: The ribosome assembles around the start codon on the mRNA. The tRNA carrying the first amino acid (methionine) binds to the P site of the ribosome.

2. Elongation: Additional tRNA molecules bring amino acids to the A site of the ribosome, where they form peptide bonds with the growing polypeptide chain in the P site. The ribosome moves along the mRNA, shifting the tRNA from the A site to the P site and empty tRNA moves to the E site to exit.

3. Termination: When the ribosome reaches a stop codon, the translation process ends, and the completed polypeptide chain is released.

15.For the transcription and translation example, using the DNA template sequence 3' GGCCTACCGAATT 5', the mRNA sequence would be 5' CCGGAUGGCUUAA 3'. The corresponding amino acid sequence would be Pro-Met-Ala-Stop, with the start codon AUG indicating the beginning of translation. The sequence of the opposite strand of DNA would be 5' CCGGATCCTAA 3'.

16.Differences in transcription and translation lead to unique cell types within the same individual because different genes are expressed in different cell types, even though all cells have the same DNA. This differential gene expression results in specialized functions and characteristics of cells, such as those in the liver or skin.

17.Types of mutations in DNA include:

1. Substitution: One nucleotide is replaced by another. Example: Original 3' TACATCCGG 5’ becomes 3' TACATCGGG 5’ (C instead of C).

2. Addition: One or more nucleotides are added. Example: Original 3' TACATCCGG 5’ becomes 3' TACCATCCGG 5’ (A added).

3. Deletion: One or more nucleotides are removed. Example: Original 3' TACATCCGG 5’ becomes 3' TACCCGG 5’ (A deleted).

4. Frameshift: Caused by addition or deletion of nucleotides that are not in multiples of three, altering the reading frame.

18.Nonsense, missense, and silent mutations can alter the amino acid sequence:

1. Nonsense: Changes an amino acid to a stop codon. Example: Original Met-Arg-Glu becomes Met-Stop.

2. Missense: Changes one amino acid to another. Example: Original Met-Arg-Glu becomes Met-Lys-Glu.

3. Silent/Neutral: No change in amino acid sequence. Example: Original Met-Arg-Glu remains Met-Arg-Glu.

19.Spontaneous mutations occur naturally without external influence, while induced mutations result from exposure to mutagens, which are agents that cause mutations.

20.A carcinogen is a substance that promotes cancer. Not all carcinogens are mutagens, but many mutagens can also be carcinogenic since they can cause changes in DNA that lead to cancer.

21.Somatic mutations occur in non-reproductive cells and are not passed on to offspring, while germ line mutations occur in reproductive cells and can be inherited. This is why somatic cell mutations do not affect future generations.

22. Chemical mutagens cause DNA changes through chemical interactions, like alkylating agents (e.g., mustard gas) and base analogs (e.g., 5-bromouracil). Physical mutagens cause mutations through physical means, such as radiation, with examples like ultraviolet light (causing thymine dimers) and ionizing radiation (breaking DNA strands).

23. Mutations impact cells and organisms in various ways:

- Negative mutations can lead to diseases like cancer and genetic disorders (e.g., cystic fibrosis).

- Positive mutations can provide advantages, aiding adaptation and evolution (e.g., better sunlight utilization in plants).

- Neutral mutations may not significantly affect fitness but contribute to genetic diversity over time.

- Mutations that increase cell reproduction can lead to diseases like cancer, characterized by uncontrolled cell growth.

24. Cells reduce mutation rates through:

- Proofreading: DNA polymerases correct errors during replication by removing incorrectly paired nucleotides.

- DNA Repair: Mechanisms like nucleotide excision and base excision repair fix damaged DNA, preventing mutations.

- Detoxification: Enzymes like cytochrome P450 metabolize harmful substances, minimizing their mutagenic effects.

These mechanisms help maintain genetic stability and prevent harmful mutations.