Molecular Biology I: How DNA Replicates
Reading
OpenStax book: Ch. 9 - "Molecular Biology" sections 9.1 & 9.2
BJU: Section 2.6 - "Proteins and nucleic acids"
AP students additional reading: Princeton Review "Gene Expression and Regulation" up through DNA Replication.
Topic
Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. Some of you want more hands-on than others. We will do what we can do.
There are lots of possible labs for this section, some are hands-on and some virtual - this is a partial list of options:
OpenStax book: Ch. 9 - "Molecular Biology" sections 9.1 & 9.2
BJU: Section 2.6 - "Proteins and nucleic acids"
AP students additional reading: Princeton Review "Gene Expression and Regulation" up through DNA Replication.
Topic
- How DNA replicates itself during cell division
Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. Some of you want more hands-on than others. We will do what we can do.
There are lots of possible labs for this section, some are hands-on and some virtual - this is a partial list of options:
- PhET Gene Expression lab
- PhET Gene Machine Lac Operon lab
- Bio-Rad DNA Fingerprinting lab (fulfills AP "dirty dozen lab" #9
- Bio-Rad Lambda DNA Restriction Digest/Electrophoresis lab (fulfills AP "dirty dozen lab #9
- Bio-Rad pGLO Bacterial Transformation lab (fulfills AP "dirty dozen lab" # 8)
- HHMI Transgenic Fly lab (fulfills AP "dirty dozen lab" #8)
- CRISPR labs (various sources)
Diagram: Unwinding and copying the two strands of DNA
Introduction
When a cell divides, it must first replicate all its DNA so that each daughter cell receives a complete copy. DNA replication occurs in all living organisms - humans, whales, finches, corn plants, and fruit flies.
DNA replication - also called DNA synthesis - uses some very interesting molecular machines within the cell. We will watch an animation, below, to get a mental snapshot of what's going on. Once you begin to realize this highly-mechanized, highly-complex process is going on in your cells - biology and biotechnology springs to life!
When a cell divides, it must first replicate all its DNA so that each daughter cell receives a complete copy. DNA replication occurs in all living organisms - humans, whales, finches, corn plants, and fruit flies.
DNA replication - also called DNA synthesis - uses some very interesting molecular machines within the cell. We will watch an animation, below, to get a mental snapshot of what's going on. Once you begin to realize this highly-mechanized, highly-complex process is going on in your cells - biology and biotechnology springs to life!
Lecture summary
When a cell divides during mitosis, it is important that each daughter cell receives an identical copy of the DNA. If it didn't, it would be dead on arrival! Think for a second: without an accurate copy of DNA, how could it make all the protein parts it needs for survival?
Copying of the DNA is accomplished by the process of DNA replication - also known as DNA synthesis. This occurs in the S phase of the cell cycle (we studied the cell cycle in a previous Unit, so you already knew that). Now you know why it's called the 'S' phase (S = synthesis). After that particular cell - let's say a skin cell - completes its synthesis phase, it then moves on the G2 phase - hopefully passes through the G2 quality checkpoint - and ultimately moves on to the mitosis phase where it actually divides. We studied the cell cycle in the Unit on mitosis, so all that should sound vaguely familiar.
DNA replication is carried out by a molecular machine known as DNA polymerase, which is a huge assemblage of many protein subunits, brought together in a specific sequence and structure just when it's needed. The DNA polymerase package - known as the replisome - acts like a moving factory, simultaneously copying one strand of DNA forwards, and the other strand of DNA backwards, by an ingenious sliding-looping-ratcheting mechanism. Your textbooks present it in diagrams, and the videos below present it as an animation.
In eukaryotes (humans, pea plants, dolphins, and yeast) DNA replication occurs in the nucleus - after all, that's where the DNA resides.
In prokaryotes (think: bacteria) DNA replication occurs right out in the open - in the cytoplasm itself; after all, that's where bacterial DNA resides.
Summary: You are learning what is called molecular biology! You are beginning to realize that you are made of trillions of complex factories, each doing its own important job to support the overall organism (you!). The beauty and complexity at this level of miniaturization is astounding... and it makes biology and biotechnology (and thus life itself) incredibly worthwhile and fascinating.
When a cell divides during mitosis, it is important that each daughter cell receives an identical copy of the DNA. If it didn't, it would be dead on arrival! Think for a second: without an accurate copy of DNA, how could it make all the protein parts it needs for survival?
Copying of the DNA is accomplished by the process of DNA replication - also known as DNA synthesis. This occurs in the S phase of the cell cycle (we studied the cell cycle in a previous Unit, so you already knew that). Now you know why it's called the 'S' phase (S = synthesis). After that particular cell - let's say a skin cell - completes its synthesis phase, it then moves on the G2 phase - hopefully passes through the G2 quality checkpoint - and ultimately moves on to the mitosis phase where it actually divides. We studied the cell cycle in the Unit on mitosis, so all that should sound vaguely familiar.
DNA replication is carried out by a molecular machine known as DNA polymerase, which is a huge assemblage of many protein subunits, brought together in a specific sequence and structure just when it's needed. The DNA polymerase package - known as the replisome - acts like a moving factory, simultaneously copying one strand of DNA forwards, and the other strand of DNA backwards, by an ingenious sliding-looping-ratcheting mechanism. Your textbooks present it in diagrams, and the videos below present it as an animation.
In eukaryotes (humans, pea plants, dolphins, and yeast) DNA replication occurs in the nucleus - after all, that's where the DNA resides.
In prokaryotes (think: bacteria) DNA replication occurs right out in the open - in the cytoplasm itself; after all, that's where bacterial DNA resides.
Summary: You are learning what is called molecular biology! You are beginning to realize that you are made of trillions of complex factories, each doing its own important job to support the overall organism (you!). The beauty and complexity at this level of miniaturization is astounding... and it makes biology and biotechnology (and thus life itself) incredibly worthwhile and fascinating.
The following videos will help you visualize what's going on during DNA replication:
| 10._dna_replication_lecture_slides.pptx |
LABS & HOMEWORK BELOW: There are numerous labs, projects, presentations, and homework exercises posted on this portal. Don't panic. Some of these are current, some are left over from prior years, and some are just "parked" here for future use. DO NOT WORK ON A LAB OR HOMEWORK EXERCISE unless it has been assigned in your weekly class email! Due to the 2020-2021 Covid-19 situation, I will assign labs and homework as we go along based on what we are able to do.
LABS & HOMEWORK BELOW: There are numerous labs, projects, presentations, and homework exercises posted on this portal. Don't panic. Some of these are current, some are left over from prior years, and some are just "parked" here for future use. DO NOT WORK ON A LAB OR HOMEWORK EXERCISE unless it has been assigned in your weekly class email! Due to the 2020-2021 Covid-19 situation, I will assign labs and homework as we go along based on what we are able to do.
Homework
| dna_replication_homework_questions.docx |
Forensic DNA Fingerprinting lab: Digestion and Electrophoresis of Crime-Scene DNA
In this 3-part lab project, we will analyze the DNA from a Crime Scene using restriction enzymes and gel electrophoresis.
The DNA-fragments from 5 "suspects" will be compared to DNA found at the Crime Scene.
This is a very important technique used in criminal justice, ancestry & anthropology research, paternity, human remains identification, and disease tracing.
The student lab handout and video tutorials are posted in the previous unit.
In this 3-part lab project, we will analyze the DNA from a Crime Scene using restriction enzymes and gel electrophoresis.
The DNA-fragments from 5 "suspects" will be compared to DNA found at the Crime Scene.
This is a very important technique used in criminal justice, ancestry & anthropology research, paternity, human remains identification, and disease tracing.
The student lab handout and video tutorials are posted in the previous unit.
DNA Fingerprinting lab follow-up homework
| 10._dna_fingerprinting_lab_followup_homework_instructions.docx |
| dna_fingerprinting_gel__with_measurements_img_5883.jpg |
Here are the "answers". The migration distances will be different, but the banding pattern is the same.
| 10._dna_fingerprinting_follow-up_homework__answers_.pdf |
Gel electrophoresis tutorial video below: