Biology- The Mitotic Cell Cycle

 

Biology

Mitotic Cell Cycle

Chapter-5

Learning Objectives:

a. Describe the structure of chromosomes
b. Describe the cell cycle- the cycle of events by which body cells grow to a certain size and then divide into two
c. explain how a nucleus divides into two genetically identical nuclei by mitosis.
d. prepare and observe a root tip squash in order to see stages of mitosis with a light microscope
e. explain the significance of mitosis
f. explain the significance of telomeres
g. explain the significance of stem cells
h. outline how uncontrolled cell division can lead to cancer.

1. During prophase of mitosis, chromosomes consist of two chromatids. At which stage of the cell cycle is the second chromatid made?

a. cytokinesis

b. G1

c. G2

d. S

2. Growth of cells and their division are balanced during the cell cycle. Which column shows the consequences that would follow from the two errors shown in the table?

3. A cell with four chromosomes undergoes a cell cycle including mitosis. Which diagram correctly shows the changes in chromatid number during interphase?

4. Distinguish between the following terms: centrosome, centriole and centromere.

5. The diagram shows three cells (labelled A, B, and C) from a root tip which have been stained to show chromosomes.

a. identify the stage of mitosis shown by each cell.

b. Describe what is happening at each stage.

6. a. Diagram 1 below shows a plant cell dividing by mitosis. Only two of the many chromosomes are shown for simplicity.

i. What stage of mitosis is shown?

ii. Draw prophase for the same cell assuming the cell has only two chromosomes, as in diagram 1.

b. Diagram 2 shows the same cell at telephase. The cell is beginning to divide and a new cell wall is forming. spreading out from the middle of the cell. Copy the diagram and add drawings of the chromosomes as they would appear at this stage.

Q.1. What is centrosphere?

Ans: Centrosphere is the differentiated layer of cytoplasm surrounding the centriole within the centrosome. 

Q.2. What do you mean by genetic code?

Ans: The genetic code is the set of rules by which information encoded in genetic material (DNA and RNA sequences) is translated into the proteins (amino acid sequences) by living cells. This code is a set of three-letter combinations of nucleotides called codons, each of which corrresponds to a specific amino acid or stop signal.

Q.3. What is germ cell?

Ans: A germ cell is any biological cell that gives rise to the gametes of an organism that reproduces sexually.

Q.4. What is nucleic acid?

Ans: Nucleic acids are the polynucleotides having high molecular weight. The monomeric unit of which is nucleotide.

Q.5. What do you mean by genetic code?

Ans: A unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring. The correspondence between specific DNA base sequences and the amino acids they specify is called code. 

Q.6. Differences between DNA and RNA are given below-

Physical structure - DNA - Double stranded

                                 RNA - Single stranded

Chemical structure- DNA has two nucleotide strands which consist of its phosphate group, five-carbon sugar (the stable 2-deoxyribose), and four nitrogen-containing nucleobases: adenine, thymine, cytosine, and guanine.

RNA - Like DNA, RNA is composed of its phosphate group, five-carbon sugar (the less stable ribose), and 4 nitrogen-containing nucleobases: adenine, uracil (not thymine), guanine, and cytosine.

Types-   DNA no types

              RNA 5 types - tRNA, rRNA, mRNA, gRNA, and minor RNA

Replication -  DNA occurs

                      - RNA does not occur.

Location - DNA is found in the nucleus, with a small amount of DNA also present in mitochondria.

               RNA forms in the nucleolus, and then moves to specialized regions of the cytoplasm depending on the type of RNA formed.

Function- DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism.

RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories.

Q. 7. Which orgenelle is called the protein making factory of cell?

Ans: Ribosome is the cell organelle which is termed as the protein factory of the cell. It gathers amino acids and assembles them into protein chains to make almost anything the cell needs. A strand of ribonucleic acid, or messenger RNA, is the template. The process through which proteins are formed with the help of mRNA and tRNA is called translation.

Q.8. The difference between transcription and translation

1) transcription is the first step of gene expression process.
a) Translation is the second step of gene expression process.

2) Synthesises RNA copies of the genetic instructions written in the genome.
b) Synthesises proteins from RNA which are copied from genes.

3) Template is the genes in the genome.
c) Template is the mRNA.

4) Occurs in the nucleus.
d) Occurs in the cytoplasm.

5) RNA polymerase are the enzymes.
e) Ribosomes are enzymes.

Q.9. What is codon?

Ans: Codon is a unit that consists of three adjacent bases on a DNA molecule and that determines the position of a specific amino acid in a protein molecule during protein synthesis.

Q.10. Which organelle is called the protein factor of cell- explain.

Ans: Ribosome is the cell organelle which is termed as protein factory of the cell. It gathers amino acids and assembles them into protein chains to make almost anything the cells needs. A strand of ribonucleic acid, or messenger RNA, is the template. The process through which proteins are formed with the help of mRNA and tRNA is called Translation.

Q.11. What are the functions of  DNA?

Ans: Functions of DNA:

a) It functions as the structural component of the chromosome.
b) It functions as the molecular basis of heredity.
c) It bears the heredity characters of organisms and transmits the characters to the next generation.
d) It regulates all the activities of the organism through protein synthesis.
e) It creates variation of character by undergoing mutation which is the raw material for evolution.
f) It is responsible for the expression or all characteristics of the organism.
g) It repairs any fault created in the structural frame of DNA molecule.