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The resting potential of the cell membrane and the process of cell cycle, including mitosis and meiosis. It explains the composition of chromosomes, DNA, and RNA, and how they are involved in protein synthesis. The document also provides multiple-choice questions and answers related to the topics.
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The cell nucleus contains chromosomes which are composed of molecules of DNA. DNA is composed of units called nucleotides which consist of a sugar (deoxy- ribose) attached to a phosphoric acid group (PO3OH) and one of four bases. Chromosomes contain the code for the sequence of amino acids used to construct different proteins. Each amino acid is coded for by a particular sequence of three of the four bases (adenine, guanine, cytosine & thymine). This sequence is called a “codon”. mRNA “transcribes” this code then moves from the nucleus to a ribosome in the cytoplasm where it is “translated” and the protein is assembled by joining the required amino acids in the appropriate sequence. Mitosis is the process by which a somatic cell divides to produce two cells with identical DNA. In this way an organism can grow. Before mitosis, the DNA must be duplicated. Hence the chromosomes (consisting of one strand or “chromatid”) dou- ble up by becoming two chromatids. Then during mitosis the two chromatids sepa- rate and move into the two daughter cells. Meiosis occurs only in the gonads. This process results in four daughter cells. Human cells have two copies of each of 23 chromosomes, one copy being inherited from the father and the other copy from the mother. The gametes need to have only one copy of each of the 23 chromosomes, so that when the sperm fuses with the ovum, the “diploid” number of 46 (two copies of each chromosome) is restored. Meiosis is the process by which cells reduce their number of chromosomes from 46 to 23 different chromosomes. Of the 23 chromosomes in a sperm (or ovum), some (between 0 and 23) will have come from the sperm owner’s mother and the rest from the sperm owner’s father. The same can be said of the 23 chromosomes in the ovum. In this way the resulting children will be genetically different from each of their parents (and siblings) as each sperm/ovum will have a different assortment of the 23 available chromosomes.
A. genetic substance B. cellular energy C. membrane support D. nuclear membrane Answer is A: Chromatin is DNA & the associated proteins so pertains to genetic material.
A. cytoplasm between ribosomes, tRNA and mRNA B. nucleus between ribosomes, tRNA and mRNA C. nucleus between DNA and mRNA D. cytoplasm between DNA and mRNA Answer is A: translation occurs in the cytoplasm (transcription occurs in the nucleus). DNA does not exist in the cytoplasm.
A. single stranded, deoxyribonucleic acid B. single stranded, ribonucleic acid C. double stranded, deoxyribonucleic acid D. double stranded, ribonucleic acid Answer is C: DNA is double stranded, while the “D” refers to “deoxy-”.
C. A codon D. A nucleotide Answer is D: three nucleotides form a codon and many codons form a chromatid.
A. spindle fi bres pull each chromatid to opposite sides of the cell B. the sense and non-sense strands “unzip” along their hydrogen bonds C. RNA polymerase forms a complementary strand by reading the sense strand D. the cell cytoplasm divides into two cells Answer is A: separation of the two chromatids of a chromosome occurs at ana- phase. Choice D is cytokinesis and begins in late anaphase and continues into telophase.
A. twenty B. fi ve C. three D. one Answer is C: A sequence of three nucleotides constitute a codon. Each codon is specifi c for one of the 20 amino acids.
A. DNA B. RNA C. mRNA D. tRNA Answer is A: DNA exists in the nucleus. The other three are ribonucleic acids.
A. A–T pair B. A–G pair C. C–T pair D. C–A pair Answer is A: A pairs with T, while C pairs with G.
A. nucleoside B. amino acid C. polypeptide D. nucleotide Answer is A: a nucleotide is formed from a nucleoside and a phosphate group.
cells – 23 each from the man’s father and mother. When sperm are produced, the 46 chromosome assemble and pair up. The man’s X and Y chromosomes pair up. Each pair of chromosomes then separates so that only one of each pair moves into a new sperm. Which one of the pair ends up in which sperm is a random process. It is possible that an individual sperm has any number of chro- mosomes between 0 and 23 that originated from the father.