DNA & RNA Structure
My AP Biology Thoughts
Unit 6 Gene Expression and Regulation
Welcome to My AP Biology Thoughts podcast, my name is Jacqueline Sun and I am your host for episode #105 called Unit 6 Gene Expression and Regulation: DNA and RNA Structure. Today we will be discussing the central structural components of DNA and RNA as well as the similarities and differences between the two.
Segment 1: Introduction to DNA and RNA Structure
- Deoxyribonucleic acid, DNA, and ribonucleic acid, RNA, are two of the most important biological molecules for survival
- DNA responsible for carrying genetic information is commonly considered the “blueprint” for life’s functions. Its basal structure, a double helix that is unique from RNA, is key to its ability to replicate itself. DNA, when not undergoing replication, is coiled up into compact structures known as chromosomes. They are wrapped around histone proteins: the degree of tightness to which they are wrapped determines how much of the DNA is expressed.
- RNA builds off of DNA and creates a template from which proteins can be created in ribosomes. Because they are based off of a parent DNA strand, RNA has a single strand instead of two.
Segment 2: More About DNA and RNA Structure
- However, there is much more to DNA and RNA Structure than the helical strands.
Lets first focus on what makes up the strands for DNA and RNA:
- Both DNA and RNA have a sugar-phosphate backbone that is key to holding the entire molecule together.
- However, the sugar in DNA is deoxyribose sugar, from which it derives its name. The sugar in RNA is ribose sugar, which has one more hydroxyl group than the sugar in DNA.
- The sugar and phosphate group in DNA and RNA alternate repeatedly. They link with a special directionality that is often denoted with a 5’ and 3’ end. This is a rather abstract concept, but basically the 5’ and 3’ indicate which carbon in a sugar molecule the phosphate group will attach itself, forming the repeating phosphate-sugar backbone.
- Another central structural component are the nitrogenous bases found in both DNA and RNA, with one key difference.
- DNA has the bases adenine, cytosine, guanine, and thymine. Adenine and guanine are known as purine bases, while cytosine and thymine are the pyrimidine bases. Purines tend to be larger than pyrimidines because purines have a double ring structure as opposed to pyrimidine’s single ring structure.
- Only purines and pyrimidines can bind together. Specifically, in DNA, adenine and thymine bind together, while cytosine and guanine bond together. They are held together by hydrogen bonds which link not only the bases, but also the two strands of DNA to form a double helix. The 1:1 ratio by which the nitrogenous bases bond (adenine=thymine, guanin=cytosine) explains how DNA molecules are able to replicate by synthesizing a new strand from a parent strand.
- RNA has the same bases of adenine, cytosine, and guanine, but the key difference is that it has uracil instead of thymine. Its purines are still adenine and guanine, but it’s pyrimidines are cytosine and uracil. Adenine will match with uracil as opposed to thymine in RNA synthesis.
- Lengthwise, DNA tends to be significantly longer than RNA.
- This is because while RNA is based on DNA, it will not code for the entire strand but only a certain segment of a strand. As a result, an RNA strand may only be a few thousand base pairs long, while DNA can reach from hundreds of thousands to millions of pairs long.
- There are also coding and non coding regions of DNA that are transcribed into RNA. The coding regions of DNA known as genes are the ones that can serve as templates for the synthesis of proteins, while the non coding regions have no role in creating proteins. However, non coding regions are still important. They provide structural support to the DNA molecules and also may act as regulators for gene expression.
- When DNA is transcribed in RNA, the coding regions become known as exons in RNA, and the noncoding regions become known as introns. In a process known as splicing, RNA will undergo modifications that cut out the non coding introns and bind together the remaining coding exons. After this, the RNA molecule is ready to be translated into proteins.
- Another key structural component of DNA that are actually made up of proteins and RNA subunits are telomeres. Telomeres are repetitive sequences of non-coding DNA that act as a protective cap for DNA strands. They prevent strands from fraying or splitting at the ends, but telomeres will shorten every time DNA replicates, which is often associated with the deterioration of life.
Segment 3: Connection to the Course
- Understanding the structure of DNA and RNA is important to understanding how both function as some of the most important macromolecules in life. For example, the unwindable double helix structure and the complementary base-pairing rules explain why DNA can replicate semi-conservatively, which is vital to our continued survival and our production of viable offspring. It is also important to understand the structural differences between DNA and RNA. These distinctions define the different capabilities of both molecules: DNA is the universal genetic code, and RNA is responsible for transcribing that code into templates used to create proteins. Faults in the structure of either DNA and RNA can potentially have disastrous ramifications on the health and function of an organism, so understanding the structure is the first step towards maximizing survival.
Thank you for listening to this episode of My AP Biology Thoughts. For more student-ran podcasts and digital content, make sure that you visit www.hvspn.com. See you next time!
Music Credits:
- “Ice Flow” Kevin MacLeod (incompetech.com)
- Licensed under Creative Commons: By Attribution 4.0 License
- http://creativecommons.org/licenses/by/4.0/
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Welcome to My AP Biology Thoughts podcast, this is episode #105 called Unit 6 Gene Expression and Regulation: DNA and RNA Structure.
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