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DNA Replication

By: HWC, Views: 4759

DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules. Replication is an essential process because, whenever a cell divides, the two new daughter cells must contain the same genetic information, or DNA, as the parent cell.

X chromosome inactivation in calico cats

By: HWC, Views: 4825

X chromosome inactivation causes a mosaic tissue effect in calico cats. what makes this female calico cat "calico." Like all mammals, this cat began her life as a single cell. That cell had two X chromosomes, one from each parent. One of the chromosomes carried a dominant allele for the ...

Transcription - Introns and exons

By: HWC, Views: 4967

In most eukaryotic genes, coding regions (exons) are interrupted by noncoding regions (introns). Exon - RNA sequences in the primary transcript that are found in the mRNA. Intron - RNA sequences between exons that are removed by splicing. During transcription, the entire gene is copied ...

Mechanisms for chromosome movement Animation

By: HWC, Views: 4876

At mitotic metaphase, the fully-formed spindle is composed of many microtubules that extend from the poles. Some of these, the kinetochore microtubules, are attached to the kinetochores of each chromosome. Kinetochores are located at the centromeres. At anaphase, sister chromatids separate and...

Immune responses Animation

By: HWC, Views: 4741

Overview of interactions in antibody-mediated and cell-mediated immunity Animation The antibody mediated immune response begins when a naive B cell encounters antigens from a pathogen, such as a bacterium. The B cell binds, processes, and displays this antigen. It is now an antigen-presenti...

What are Taste Receptors? How Does it Work? Animation

By: HWC, Views: 4751

Do you ever wonder how you can taste the foods you eat? It all starts with taste receptors in your muscular tongue. Taste receptor neurons are found in your taste buds but you are not looking at the taste buds. The raised bumps on the surface of the tongue that you see are specialized epith...

Complement Proteins Animation

By: HWC, Views: 4667

Formation of membrane attack complexes. Complement proteins can activate when they bind to antibodies that are bound to a pathogen. Complement proteins also activate when they bind directly to bacterial surfaces. Cascading reactions yield huge numbers of different types of complement protei...

Chemical Synapse Animation

By: HWC, Views: 5278

A neuromuscular junction is a chemical synapse between the axon endings of a motor neuron and a muscle cell. A narrow synaptic cleft separates the presynaptic cell (the motor neuron) from the postsynaptic cell (the muscle cell). The presynaptic cell contains vesicles filled with neurotransmitt...

Genetic distance between human groups

By: HWC, Views: 4747

One proposed family tree for modern humans. This family tree is based on nucleic-add hybridization studies of many genes and immuno-logical comparisons. Branch points show presumed genetic divergences. This data indicates that the greatest genetic distance separates humans native to Afri...