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3 very important cell processes:

3 very important cell processes:. DNA Replication Transcription Translation. DNA Replication. Happen in the cell’s nucleus When a cell divides, the two daughter cells need a copy of the original cell’s DNA Makes an exact copy of the original DNA molecule C matches with G (or G with C)

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3 very important cell processes:

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  1. 3 very important cell processes: • DNA Replication • Transcription • Translation

  2. DNA Replication • Happen in the cell’s nucleus • When a cell divides, the two daughter cells need a copy of the original cell’s DNA • Makes an exact copy of the original DNA molecule • C matches with G (or G with C) • A matches with T (or T with A) • Check this out: http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html

  3. Transcription • Message (or code) of DNA nucleotide sequences copied from DNA to mRNA (messenger RNA) • C on DNA matches with G on mRNA (or G on DNA matches with C on mRNA • T on DNA matches with A on mRNA (or A on DNA matches with U on mRNA) • Completed mRNA carries message from DNA and leaves the cell nucleus to the cytoplasm (at the ribosomes) where next process occurs (translation)

  4. Translation • Message from mRNA (order of nucleotides came from DNA) is translated to a specific protein • tRNA (transfer RNA) looks for a specific amino acid (ex: leucine) in the cytoplasm that it can take to the ribosome to join with a certain codon (3 letter mRNA sequence), joining other amino acids to form a polypeptide (protein) • tRNA then free to find more of the same amino acid to make more protein

  5. Questions 1-3, p 233 • How many types of nucleotides are in DNA , and how do they differ? • Four, their nitrogen-containing bases differ • How are the base pairing rules related to Chargaff’s research on DNA? • Because only A pairs with T and C pairs with G, DNA will always have approximately the same proportion of A and T and same proportion of C and G. • Explain how the double helix model of DNA built on the research of Rosalind Franklin. - Franklin’s data suggested that DNA was a helix made of two strands an even width apart. From this, Watson and Crick realized that a base with one ring would bond with the base with two rings.

  6. Questions 4-6, p 233 • Infer – Which part of a DNA molecule carries the genetic instructions that are unique for each individual: the sugar-phosphate backbone or nitrogen-containing bases? Explain. • The backbone is the same in all DNA. The nitrogen-containing bases provide the unique instructions. • Predict – In a sample of yeast DNA, 31.5% of the bases are adenine (A). Predict the approximate percentage of C, G, and T. Explain. • Matching A, T, is approximately 31.5 percent. Thus, C and G together make up 37 percent of the bases, so each makes up approximately 18.5 percent of the bases. • Evolution – The DNA of all organisms contain the same four bases (adenine, thymine, cytosine and guanine). What might this similarity indicate about the origins of life on Earth? • It suggests that the wide diversity of life that we see might have stemmed from a common ancestor.

  7. Questions 1-3, p 238 • Explain the function of replication. • To make a copy of all of the DNA in a cell so it can be passed on to a new cell. • Explain how DNA serves as its own template during replication. • Both strands act as a template. Because base pairing is specific, the sequence of one strand dictates what the sequence of the other strand has to be. • How do cells help ensure that DNA replication is accurate? • Certain types of DNA polymerase have a built in proofreading function that corrects most mispaired nucleotides.

  8. Questions 4-6, p 238 • Summarize – Describe two major functions of DNA polymerase. • DNA polymerase bond nucleotides together and proofread to ensure accuracy. • Infer – Why is it important that human chromosomes have many origins of replication? • Each chromosome in a eukaryotic cell is very long. If replication started at only one place, it would take a very long time to finish. Multiple origins of replication let the process happen more quickly. • Cell Biology – DNA is replicated before mitosis and meiosis. How does the amount of DNA produced in a cell during mitosis compare with that produced during meiosis? • Cells produced by mitosis typically have twice the amount of DNA as cells produced by meiosis.

  9. Questions 1-3, p 242 • What is the central dogma? - It is a statement that summarizes how information flows in one direction from DNA to RNA to proteins. • Why can the mRNA strand made during transcription be thought of as a mirror image of the DNA strand from which it is made? • The mRNA chain is complementary to the DNA molecule. Like a mirror image, the mRNA chain has a distinct relationship to the DNA molecule, but it is not identical to it. • Why might a cell make lots of rRNA but only one copy of DNA? - rRNA is a component of ribosomes, and many ribosomes are needed to keep up with the level of protein synthesis needed by a cell. In contrast, each cell needs only one set of DNA, so it is copied only in preparation for cell division.

  10. Questions 4-5, p 242 • Apply – If a DNA segment has the nucleotide AGCCTAA, what would be the nucleotide sequence of the complementary RNA strand? • UCGGAUU • Synthesize – What might geneticists learn about genes by studying RNA? - Because mRNA codes for only a single gene, studying mRNA can help researchers learn where genes begin and end on a chromosome. It could also indicate what genes are active in specific types of cells.

  11. Questions 1-3, p 247 • Explain the connection between a codon and an amino acid. • A codon is a sequence of three nucleotides that specifies a specific amino acid. Students may describe the physical connection between these two as the tRNA molecule. Each tRNA molecule binds to a specific amino acid and has an anticodon that binds to a specific codon. • Briefly describe how the process of translation is started. • The small ribosomal sub-unit binds to the mRNA strand at the start codon, which binds to the first tRNA molecule. • Synthesize – Suppose a tRNA molecule had the anticodon AGU. What amino acid would it carry? • That tRNA molecule would recognize the mRNA codon UCA, so it would carry the amino acid serine.

  12. Questions 4 & 5, p 247 • Hypothesize – The DNA of eukaryotic cells has many copies of genes that code for RRNA molecules. Suggest a hypothesis to explain why a cell needs so many copies of these genes. • rRNA is critical for making ribosomes to carry out protein synthesis. rRNA must be made in sufficient quantities to keep up with a cell’s demands for various proteins. • Biochemical Reactions – Enzymes have shapes that allow them to bind to a substrate. Some types of RNA also form specific three-dimensional shapes. Why do you think that RNA, but not DNA catalyzes biochemical reactions? • DNA is usually in double-stranded form, wrapped up and condensed to make it compact, not in a catalytic form. In contrast, hydrogen bonds form between the nucleotides of a single strand of RNA, causing it to form a catalytic structure.

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