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Meiosis II

JoVE 10768

Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 chromosomes—one from each homologous initial pair. Importantly, each chromosome in these cells is composed of two joined copies, and when these cells enter meiosis II, the goal is to separate such sister chromatids using the same microtubule-based network employed in other division processes. The result of meiosis II is two haploid cells, each containing only one copy of all 23 chromosomes. Depending on whether the process occurs in males or females, these cells may form eggs or sperm, which—when joined through the process of fertilization—may yield a new diploid individual. Although the goal of meiosis II is the same in both males and females—to produce haploid egg or sperm cells—there are some critical differences in this process between the sexes. For example, in a woman’s egg precursor cells, the meiotic spindle apparatus responsible for separating sister chromatids forms off to one side, near the periphery. This asymmetry allows for two cells of unequal sizes to be produced following meiosis II: a large egg, and a smaller polar body that dissolves. This division of cytoplasm ensures that the egg contains enough nutrients to support an embryo. The position of the meiotic spind

 Core: Biology

Photosystem II

JoVE 10751

Photosystem II is a multi-protein complex embedded within the thylakoid membrane where it harvests light energy. Chlorophyll molecules transfer energy to a specific pair of chlorophyll a molecules in the reaction center of Photosystem II. Here, the chlorophyll a molecules lose an electron (oxidation), transferring it to a primary electron acceptor. The donated electrons pass through the electron transport chain into Photosystem I. Splitting a water molecule releases one oxygen atom, two protons (H+) and two electrons. The electrons replace the donated electrons of the two chlorophyll a molecules in the reaction center. The oxygen atom immediately reacts with another oxygen atom, producing O2 that is released into the atmosphere. The protons accumulate and create a concentration gradient across the thylakoid membrane that drives ATP synthesis in a process called chemiosmosis. The multi-protein complex Photosystem II harvests photons and transfers energy through its bound pigments chlorophyll a and b, and carotenoids. Carotenoids have a protective function as they help dissipate the vast amount of energy taken in that could otherwise damage the plant tissue. Energy travels from chlorophyll molecule to chlorophyll molecule until it reaches a pair of specialized chlorophyll a molecules in a region called the re

 Core: Biology

Synthesis of an Oxygen-Carrying Cobalt(II) Complex

JoVE 10430

Source: Deepika Das, Tamara M. Powers, Department of Chemistry, Texas A&M University


Bioinorganic chemistry is the field of study that investigates the role that metals play in biology. Approximately half of all proteins contain metals and it is estimated that up to one third of all proteins rely on metal-containing active sites to…

 Inorganic Chemistry

Cranial Nerves Exam II (VII-XII)

JoVE 10005

Source:Tracey A. Milligan, MD; Tamara B. Kaplan, MD; Neurology, Brigham and Women's/Massachusetts General Hospital, Boston, Massachusetts, USA


The cranial nerve examination follows the mental status evaluation in a neurological exam. However, the examination begins with observations made upon greeting…

 Physical Examinations III

Compound Administration II

JoVE 10388

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN



Compound administration is often an integral component of an animal study. Many factors need to be evaluated to ensure that the compound is delivered correctly. The route of administration affects the mechanisms of…

 Lab Animal Research

Blood Withdrawal II

JoVE 10247

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN


The collection of blood from mice and rats for analysis can be done through a variety of methods. Each method of collection has variations in the type of restraint required, the invasiveness of the procedure, and the necessity of a general …

 Lab Animal Research

Shoulder Exam II

JoVE 10185

Source: Robert E. Sallis, MD. Kaiser Permanente, Fontana, California, USA


The shoulder exam continues by checking the strength of the rotator cuff muscles and biceps tendons. The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) act as compressors, holding the humeral head in place against the glenoid.…

 Physical Examinations III

Rodent Identification II

JoVE 10182

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN


Animal records must be accurately maintained to ensure that data collection is correct. Records range from maintaining information on cage cards to having a detailed database with all of the relevant information on each animal. The primary …

 Lab Animal Research

Pelvic Exam II: Speculum Exam

JoVE 10141

Source:


Alexandra Duncan, GTA, Praxis Clinical, New Haven, CT


Tiffany Cook, GTA, Praxis Clinical, New Haven, CT


Jaideep S. Talwalkar, MD, Internal Medicine and Pediatrics, Yale School of Medicine, New Haven, CT


Providing…

 Physical Examinations II
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