A DNA lesion is any change to a DNA molecule that disrupts its normal chemical structure. This excludes DNA polymerase so-called " errors." In the case of errors, while there is a non-complementary pair of nucleotides in the double helix, the chemical structure of the nucleotide molecules remains intact. In this post, we'll discuss the the DNA repair pathways that correct the vast majority of DNA lesions. These include ribonucleotide excision repair (RER) , base excision rep

Life can't exist without the high fidelity transmission of genetic information from parent cell to daughter cell. DNA polymerases plays a big role in accomplishing this. DNA polymerases delta and epsilon only make an error (that is, attach a non-complementary nucleotide to a growing chain) once every 100,000 to 1 million nucleotide additions. But this is too many. They'll need to be fixed via a back-up system that we'll soon be discussing. In addition, the human genome--eve

As the CMG helicase moves along the double helix separating it into a leading and a lagging strand, it creates what is often referred to...

DNA polymerases can only synthesize DNA in the 5' to 3' direction. That is an absolute rule that's determined by the biochemistry of nucleotide addition. Given the antiparallel nature of DNA, a corollary is that DNA polymerases can only synthesize off template DNA that is oppositely oriented in the 3' to 5' direction. Our leading strand exited the MCM2-7 ring of the CMG helicase 3' end first. So the DNA strand that will be synthesized using that strand as a template will be s

An important fact: The two DNA strands in a double helix are oriented in an antiparallel manner. That is, they run in opposite directions like the lanes of a two-lane highway. Recalling chapter ___, scientists describe the orientation of a given single strand of DNA as running either “3’-to-5’” (three prime to five prime) or “5’-to-3’” (five prime to three prime) based on the orientations of the deoxyribose sugars in the DNA backbone. But as a hard and fast rule, DNA polymera

Let's take a closer look at two amazing molecular machines found in the replisome: the CMG helicase and the PCNA sliding clamp . Both...

Our cell of interest is now in S phase and 30,000-50,000 replication origins along its genome have become licensed. The replication...

As we kick off the focus of this book—a deep dive into human genome replication—we’ll see that the process involves many different...

If someone had wanted a book in the 15th century it would have had to have been copied by hand from an existing one. The scribe would...

In this post I present a perfect example of ATP-driven protein motor movement. ATP is a frequently employed driver of protein movement in...

Each time a cell divides, it creates a copy of both its genomes for the two daughter cells. It does so with extremely high accuracy (or...

A cell is a dynamic place. Enzymes are speeding up chemical reactions. DNA, RNA, and proteins are being synthesized. Molecular motors are...

Two human genomes adding up to 6 billion base pairs are contained in the nucleus of every cell in your body. Different kinds of cells use...

We've covered proteins : polymers of amino acid monomers that fold up and perform most of the tasks in the cell. We've also covered DNA...

My last post covered the structure of DNA: what DNA is. In this post, I move on to function: what DNA does, or, maybe better, how DNA...

In this "Part I" post I'll be focusing on the structure of DNA--what DNA is . In the next, I'll cover how DNA functions--what it does ....

Most of the time, most of your cells are simply doing their jobs. Neurons in your brain are sending electrochemical signals. Cardiac...

In the last post I likened a human cell to a factory and then I extended the analogy to characterize the major components of a cell. In...

A 30,000-foot view. Proteins account for about 50% of the cell's weight. That's much more than DNA, which accounts for 1-2%. It's also...

Analogies are ubiquitous in molecular biology. Traditionally, two analogies have been used to describe the cell: the cell as a factory and the cell as a city . Some will say these analogies are overused. I disagree. They are heavily used because they are effective. We’ll use the factory analogy. I like it a bit better because, like a factory, cells perform specific jobs—they have a specific output or function. Cities don’t have a primary function or output.   So, let’s think