[Tissue hemoglobins of Gastropoda (Mollusca)]

Hemoglobin is a globular protein made up of four subunits. Two of these subunits are alpha chains, and the other two are beta chains. Each subunit contains a molecule of heme, which has an iron atom and can bind to oxygen. When an oxygen molecule binds to one heme group, it changes the shape of hemoglobin, making it easier for the other heme groups to bind oxygen as well.
When all four heme groups are bound to oxygen, the resulting molecule is called oxyhemoglobin. As a result, arterial blood...

Hemoglobin (Hb) is a crucial molecule in the human body, consisting of four polypeptide chains, each bound to an iron-containing heme group. This unique structure enables hemoglobin to bind to oxygen, with each molecule capable of combining with four molecules of oxygen, leading to rapid and reversible oxygen loading. When fully loaded with oxygen, it is called oxyhemoglobin, while hemoglobin that has released oxygen is called reduced hemoglobin or deoxyhemoglobin. As hemoglobin binds oxygen,...

Gene families consist of groups of genes proposed to have originated from a common ancestor. Typically these arise through events in which a gene or genes are mistakenly duplicated during cell division. Unlike their parent genes (which are subject to selection pressure to maintain function), these gene copies do not need to preserve their sequences and may evolve at a relatively faster rate.
Occasionally these regions can be adapted to take on new roles within the organism, becoming novel genes...

The GI tract, from beginning to end, is made up of four continuous tissue layers that adjust their structure according to their specific roles. These layers, from innermost to outermost, are known as the mucosa, submucosa, muscularis, and serosa, which are continuous with the mesentery.
The mucosa is sometimes called a mucous membrane due to its mucus-secreting features. This membrane is composed of epithelium, which directly interacts with ingested substances, and the lamina propria, a layer...

In organisms, proteins are the most abundant macromolecules. They act as the building blocks of life and play various crucial roles in the body. Proteins can be broadly classified into two distinct subtypes based on their shape and solubilities: globular proteins and fibrous proteins.
Globular proteins serve many important physiological functions, such as acting as enzymes, cellular messengers, and molecular transporters. These roles often require the proteins to be soluble in the aqueous...

Cells with similar structure and function are grouped into tissues. A group of tissues with a specialized function is called an organ. There are four main types of tissue in vertebrates: epithelial, connective, muscle, and nervous.