
Concept explainers
During the contraction of a vertebrate skeletal muscle fiber, calcium ions
- A. break cross-bridges by acting as a cofactor in the hydrolysis of ATP.
- B. bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed.
- C. transmit action potentials from the motor neuron to the muscle fiber.
- D. spread action potentials through the T tubules.

Introduction:
Skeletal muscles are voluntary muscles that are attached to bones by tendons. They help in the movement of various body parts in relation to each other.
Answer to Problem 1TYU
Correct answer:
During the contraction of a vertebrate skeletal muscle fiber, calcium ions bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed. Therefore, option (B) is correct.
Explanation of Solution
Reasons for the correct statement:
Calcium ions (Ca2+) and actin binding proteins play an important role in muscle contraction and relaxation. Tropomyosin and troponin complex are proteins bound to thin filaments (actin filaments).
In muscle fiber at rest, a regulatory protein called tropomyosin covers the binding site of myosin protein, thereby preventing the interaction of actin and myosin.
The arrival of action potential causes release of calcium ions from the sarcoplasmic reticulum. The calcium ions bind to troponin complex causing the tropomyosin to shift away from the myosin-binding sites, thereby allowing the contraction of muscle.
Option (B) is given as “bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed”.
As, “during the contraction of a vertebrate skeletal muscle fiber, calcium ions bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed”, it is the right answer.
Hence, option (B) is correct.
Reasons for the incorrect statements:
Option (A) is given as “break cross-bridges by acting as a cofactor in the hydrolysis of ATP”.
Calcium ions promote the formation of cross-bridges between actin and myosin, so it is a wrong answer.
Option (C) is given as “transmit action potentials from the motor neuron to the muscle fiber”.
The acetylcholine (neurotransmitter), but not the calcium ions transmits action potential from the motor neuron to the muscle fiber, so it is a wrong answer.
Option (D) is given as “spread action potential through the T tubules”.
The binding of acetylcholine to its receptors on the plasma membrane of a muscle fiber triggers action potential which spread through the T-tubules. The calcium ions do not spread action potential through the T-tubules, so it is a wrong answer.
Hence, options (A), (C), and (D) are incorrect.
Calcium ions play an important role in muscle contraction.
Want to see more full solutions like this?
Chapter 39 Solutions
CAMPBELL BIOLOGY IN FOCUS-W/MASTR.BIO.
Additional Science Textbook Solutions
Laboratory Manual For Human Anatomy & Physiology
Applications and Investigations in Earth Science (9th Edition)
Chemistry
Microbiology Fundamentals: A Clinical Approach
- Ch.23 How is Salmonella able to cross from the intestines into the blood? A. it is so small that it can squeeze between intestinal cells B. it secretes a toxin that induces its uptake into intestinal epithelial cells C. it secretes enzymes that create perforations in the intestine D. it can get into the blood only if the bacteria are deposited directly there, that is, through a puncture — Which virus is associated with liver cancer? A. hepatitis A B. hepatitis B C. hepatitis C D. both hepatitis B and C — explain your answer thoroughlyarrow_forwardCh.21 What causes patients infected with the yellow fever virus to turn yellow (jaundice)? A. low blood pressure and anemia B. excess leukocytes C. alteration of skin pigments D. liver damage in final stage of disease — What is the advantage for malarial parasites to grow and replicate in red blood cells? A. able to spread quickly B. able to avoid immune detection C. low oxygen environment for growth D. cooler area of the body for growth — Which microbe does not live part of its lifecycle outside humans? A. Toxoplasma gondii B. Cytomegalovirus C. Francisella tularensis D. Plasmodium falciparum — explain your answer thoroughlyarrow_forwardCh.22 Streptococcus pneumoniae has a capsule to protect it from killing by alveolar macrophages, which kill bacteria by… A. cytokines B. antibodies C. complement D. phagocytosis — What fact about the influenza virus allows the dramatic antigenic shift that generates novel strains? A. very large size B. enveloped C. segmented genome D. over 100 genes — explain your answer thoroughlyarrow_forward
- What is this?arrow_forwardMolecular Biology A-C components of the question are corresponding to attached image labeled 1. D component of the question is corresponding to attached image labeled 2. For a eukaryotic mRNA, the sequences is as follows where AUGrepresents the start codon, the yellow is the Kozak sequence and (XXX) just represents any codonfor an amino acid (no stop codons here). G-cap and polyA tail are not shown A. How long is the peptide produced?B. What is the function (a sentence) of the UAA highlighted in blue?C. If the sequence highlighted in blue were changed from UAA to UAG, how would that affecttranslation? D. (1) The sequence highlighted in yellow above is moved to a new position indicated below. Howwould that affect translation? (2) How long would be the protein produced from this new mRNA? Thank youarrow_forwardMolecular Biology Question Explain why the cell doesn’t need 61 tRNAs (one for each codon). Please help. Thank youarrow_forward
- Molecular Biology You discover a disease causing mutation (indicated by the arrow) that alters splicing of its mRNA. This mutation (a base substitution in the splicing sequence) eliminates a 3’ splice site resulting in the inclusion of the second intron (I2) in the final mRNA. We are going to pretend that this intron is short having only 15 nucleotides (most introns are much longer so this is just to make things simple) with the following sequence shown below in bold. The ( ) indicate the reading frames in the exons; the included intron 2 sequences are in bold. A. Would you expected this change to be harmful? ExplainB. If you were to do gene therapy to fix this problem, briefly explain what type of gene therapy youwould use to correct this. Please help. Thank youarrow_forwardMolecular Biology Question Please help. Thank you Explain what is meant by the term “defective virus.” Explain how a defective virus is able to replicate.arrow_forwardMolecular Biology Explain why changing the codon GGG to GGA should not be harmful. Please help . Thank youarrow_forward
- Stage Percent Time in Hours Interphase .60 14.4 Prophase .20 4.8 Metaphase .10 2.4 Anaphase .06 1.44 Telophase .03 .72 Cytukinesis .01 .24 Can you summarize the results in the chart and explain which phases are faster and why the slower ones are slow?arrow_forwardCan you circle a cell in the different stages of mitosis? 1.prophase 2.metaphase 3.anaphase 4.telophase 5.cytokinesisarrow_forwardWhich microbe does not live part of its lifecycle outside humans? A. Toxoplasma gondii B. Cytomegalovirus C. Francisella tularensis D. Plasmodium falciparum explain your answer thoroughly.arrow_forward
- Human Physiology: From Cells to Systems (MindTap ...BiologyISBN:9781285866932Author:Lauralee SherwoodPublisher:Cengage LearningConcepts of BiologyBiologyISBN:9781938168116Author:Samantha Fowler, Rebecca Roush, James WisePublisher:OpenStax College
- Comprehensive Medical Assisting: Administrative a...NursingISBN:9781305964792Author:Wilburta Q. Lindh, Carol D. Tamparo, Barbara M. Dahl, Julie Morris, Cindy CorreaPublisher:Cengage LearningAnatomy & PhysiologyBiologyISBN:9781938168130Author:Kelly A. Young, James A. Wise, Peter DeSaix, Dean H. Kruse, Brandon Poe, Eddie Johnson, Jody E. Johnson, Oksana Korol, J. Gordon Betts, Mark WomblePublisher:OpenStax CollegeHuman Biology (MindTap Course List)BiologyISBN:9781305112100Author:Cecie Starr, Beverly McMillanPublisher:Cengage Learning





