What Is the Function of Ribosomes? This Escherichia coli cell has been treated with chemicals and sectioned so its DNA and ribosomes are clearly visible. Figure 7: The ribosome and translation.
A ribosome is composed of two subunits: large and small. Figure 8: The major steps of translation. Cellular DNA contains instructions for building the various proteins the cell needs to survive. In order for a cell to manufacture these proteins, specific genes within its DNA must first be transcribed into molecules of mRNA; then, these transcripts must be translated into chains of amino acids, which later fold into fully functional proteins.
Although all of the cells in a multicellular organism contain the same set of genetic information, the transcriptomes of different cells vary depending on the cells' structure and function in the organism. Cell Biology for Seminars, Unit 2. Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe.
Brain Metrics. Mind Read. Eyes on Environment. Accumulating Glitches. Saltwater Science. Microbe Matters. You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast. As you may know, I have been teaching BIO and also the BIO Lab to non-traditional students in an adult education program for about twelve years now. Every now and then I muse about it publicly on the blog see this , this , this , this , this , this and this for a few short posts about various aspects of it - from the use of videos, to the use of a classroom blog, to the importance of Open Access so students can read primary literature.
The quality of students in this program has steadily risen over the years, but I am still highly constrained with time: I have eight 4-hour meetings with the students over eight weeks. In this period I have to teach them all of biology they need for their non-science majors, plus leave enough time for each student to give a presentation on the science of their favorite plant and animal and for two exams.
Thus I have to strip the lectures to the bare bones, and hope that those bare bones are what non-science majors really need to know: concepts rather than factoids, relationship with the rest of their lives rather than relationship with the other sciences. Thus I follow my lectures with videos and classroom discussions, and their homework consists of finding cool biology videos or articles and posting the links on the classroom blog for all to see.
A couple of times I used malaria as a thread that connected all the topics - from cell biology to ecology to physiology to evolution. I think that worked well but it is hard to do.
They also write a final paper on some aspect of physiology. Another new development is that the administration has realized that most of the faculty have been with the school for many years. We are experienced, and apparently we know what we are doing. Thus they recently gave us much more freedom to design our own syllabus instead of following a pre-defined one, as long as the ultimate goals of the class remain the same. I am also worried that, since I am not actively doing research in the lab and thus not following the literature as closely, that some of the things I teach are now out-dated.
Not that anyone can possibly keep up with all the advances in all the areas of Biology which is so huge, but at least big updates that affect teaching of introductory courses are stuff I need to know. I need to catch up and upgrade my lecture notes. And what better way than crowdsource! So, over the new few weeks, I will re-post my old lecture notes note that they are just intros - discussions and videos etc.
If I got something wrong or something is out of date, let me know but don't push just your own preferred hypothesis if a question is not yet settled - give me the entire controversy explanation instead. If something is glaringly missing, let me know. If something can be said in a nicer language - edit my sentences.
If you are aware of cool images, articles, blog-posts, videos, podcasts, visualizations, animations, games, etc. And at the end, once we do this with all the lectures, let's discuss the overall syllabus - is there a better way to organize all this material for such a fast-paced class.
See the previous lectures:. Biology and the Scientific Method. This is known collectively as the human genome. The human genome contains around 30 genes, each of which codes for one protein. Large stretches of DNA in the human genome are transcribed but do not code for proteins. The nucleotide sequence of the human genome is now known to a reasonable degree of accuracy but we do not yet understand why so much of it is non-coding.
Some of this non-coding DNA controls gene expression but the purpose of much of it is not yet understood. This is a fascinating subject that is certain to advance rapidly over the next few years. Each time a cell divides, each of its double strands of DNA splits into two single strands. Each of these single strands acts as a template for a new strand of complementary DNA. As a result, each new cell has its own complete genome. This process is known as DNA replication.
Replication is controlled by the Watson-Crick pairing of the bases in the template strand with incoming deoxynucleoside triphosphates, and is directed by DNA polymerase enzymes. It is a complex process, particularly in eukaryotes, involving an array of enzymes. A simplified version of bacterial DNA replication is described in Figure 2. DNA biosynthesis proceeds in the 5'- to 3'-direction. This makes it impossible for DNA polymerases to synthesize both strands simultaneously.
A portion of the double helix must first unwind, and this is mediated by helicase enzymes. The leading strand is synthesized continuously but the opposite strand is copied in short bursts of about bases, as the lagging strand template becomes available. The resulting short strands are called Okazaki fragments after their discoverers, Reiji and Tsuneko Okazaki.
Strangely, DNA polymerases cannot initiate DNA synthesis de novo , but require a short primer with a free 3'-hydroxyl group. Pol III can then take over, but it eventually encounters one of the previously synthesized short RNA fragments in its path. The gap is filled by DNA ligase, an enzyme that makes a covalent bond between a 5'-phosphate and a 3'-hydroxyl group Figure 3.
The initiation of DNA replication at the leading strand is more complex and is discussed in detail in more specialized texts. DNA safely and stably stores genetic material in the nuclei of cells as a reference, or template. Meanwhile, mRNA is comparable to a copy from a reference book because it carries the same information as DNA but is not used for long-term storage and can freely exit the nucleus.
Transcription is carried out by an enzyme called RNA polymerase and a number of accessory proteins called transcription factors. Transcription factors can bind to specific DNA sequences called enhancer and promoter sequences in order to recruit RNA polymerase to an appropriate transcription site.
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