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Chapter 7 DNA Answers Humane Life Cycles 1
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The answers to Chapter 7 DNA Human Life Cycles 1
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Hoofdstuk 7: From DNA to protein: How cells read the genome(53+54). Central dogma of molecular biology: when a particular protein is needed by the cell, the
nucleotide sequence of the appropriate segment of a DNA molecule is first copied into another type
of nucleic acid RNA (ribonucleic acid). That DNA segment is called a gene, and the resulting RNA
copies are then used to direct protein synthesis. So, the flow of genetic information in cells is from
DNA to RNA to protein. This process happens in all cells. From cells in bacteria to those in humans,
they carry their genetic information this way.
(56). Difference between RNA and DNA chemically: (1) the nucleotides in RNA are ribonucleotides,
they contain the sugar ribose rather than deoxyribose found in DNA; and (2) although RNA, like DNA,
contains the bases adenine (A), guanine (G), and cytosine (C), it contains uracil (U) rather than
thymine (T) found in DNA; and (3) while DNA in cells always occurs as a double-stranded helix, RNA
is largely single-stranded and can fold as a result.
(57). RNA polymerase that catalyzes the process of transcription of protein codes has 2 functions:
The enzym RNA polymerase links covalently the growing RNA chain to ribonucleoside triphosphate.
RNA polymerases catalyze the formation of the phosphodiester bonds that link the nucleotides
together and form the sugar–phosphate backbone of the RNA chain. The RNA polymerase moves
stepwise along the DNA, unwinding the DNA helix just ahead to expose a new region of the template
strand for complementary base-pairing. In this way, the growing RNA chain is elongated by one
nucleotide at a time in the 5ʹ-to-3ʹ direction. The incoming ribonucleoside triphosphates (ATP, CTP,
UTP, and GTP) provide the energy needed to drive the reaction forward, analogous to the process of
DNA synthesis.
(58). Type of Polymerase -> Genes Transcribed
RNA polymerase I -> most rRNA genes
RNA polymerase II -> all protein-coding genes, miRNA genes, and genes for other noncoding RNAs.
RNA polymerase III -> tRNA genes, 5S rRNA gene, genes for many other small RNAs.
(59). The RNA chain produced by transcription—the RNA transcript— has a nucleotide sequence
exactly complementary to the strand of DNA used as the template.
(61). Type of RNA and function
Messenger RNAs (mRNAs) code for proteins.
Ribosomal RNAs (rRNAs) form the core of the ribosome’s structure and catalyze protein synthesis.
MicroRNAs (miRNAs) regulate gene expression.
Transfer RNAs (tRNAs) serve as adaptors between mRNA and amino acids during protein synthesis.
Other noncoding RNAs used in RNA splicing, gene regulation, telomere maintenance, and many
other processes.
(62). TFIIH pries apart the double helix at the transcription start point, using the energy of ATP
hydrolysis, which exposes the template strand of the gene. TFIIH also phosphorylates RNA
polymerase II, releasing the polymerase from most of the general transcription factors, so it can
begin transcription. The site of phosphorylation is a long polypeptide “tail” that extends from the
polymerase. Once the polymerase moves away from the promoter, most of the general transcription
factors are released from the DNA; the exception is TFIID, which remains bound through multiple
rounds of transcription initiation. (NIET AF)
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