If it receives the correct signal from the ribosome, it will then hunt down amino acid subunits in the cytoplasm and bring them to the ribosome to be built into proteins 5. Ribosomes are formed in an area of the nucleus called the nucleolus, before being exported to the cytoplasm, where some ribosomes float freely. Other cytoplasmic ribosomes are bound to the endoplasmic reticulum, a membranous structure that helps process proteins and export them from the cell 5.
Meet The Author. Ruairi J Mackenzie. Chosen for you. Deoxyribonucleic Acid. Ribonucleic Acid. DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism. RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories. All nucleotides are made of three subunits: one or more phosphate groups, a pentose sugar five-carbon sugar, either deoxyribose or ribose , and a nitrogen-containing base either adenine, cytosine, guanine, thymine, or uracil.
Each nucleotide is made of one of the five nitrogenous bases, a pentose sugar ribose or deoxyribose and a phosphate group. The five nitrogenous bases are classified as pyrimidines cytosine, thymine, and uracil , which have a ring structure; and purines adenine and guanine , which have a double-ring structure.
RNA molecules may have up to few-thousand nucleotides and are singlestranded, whereas DNA molecules have billions of nucleotides organized in two strings of nucleotides forming a helix. Study Questions Write your answer in a sentence form do not answer using loose words.
What is a nucleic acid? What elements are nucleic acids made of? What are the monomers that make the building blocks of nucleic acids? In prokaryotes, the DNA is not enclosed in a membranous envelope.
Each nucleotide is made up of three components: a nitrogenous base, a pentose five-carbon sugar called ribose, and a phosphate group.
RNA Structure : A nucleotide is made up of three components: a nitrogenous base, a pentose sugar, and one or more phosphate groups.
Adenine A , guanine G , and cytosine C are present, but instead of thymine T , a pyrimidine called uracil U pairs with adenine. The DNA molecules never leave the nucleus but instead use an intermediary to communicate with the rest of the cell. This is called transcription. The mRNA then carries the code out of the nucleus to organelles called ribosomes for the assembly of proteins.
Once the mRNA has reached the ribosomes, they do not read the instructions directly. It then reads the sequence in sets of three bases called codons. Each possible three letter arrangement of A,C,U,G e. The ribosome acts like a giant clamp, holding all of the players in position, and facilitating both the pairing of bases between the messenger and transfer RNAs, and the chemical bonding between the amino acids.
These subunits do not carry instructions for making a specific proteins i. Privacy Policy. Skip to main content. Biological Macromolecules. Search for:. Nucleic Acids.
Learning Objectives Describe the structure of nucleic acids and the types of molecules that contain them. Both DNA and RNA are made from nucleotides, each containing a five-carbon sugar backbone, a phosphate group, and a nitrogen base.
The sugar and phosphate make up the backbone, while the nitrogen bases are found in the center and hold the two strands together. The nitrogen bases can only pair in a certain way: A pairing with T and C pairing with G. This is called base pairing. Due to the base pairing , the DNA strands are complementary to each other, run in opposite directions, and are called antiparallel strands.
Key Terms mutation : any error in base pairing during the replication of DNA sugar-phosphate backbone : The outer support of the ladder, forming strong covalent bonds between monomers of DNA. Take a moment to review the nitrogenous bases in Figure 1. Identify functional groups as described in class. For each functional group identified, describe what type of chemistry you expect it to be involved in.
Try to identify whether the functional group can act as either a hydrogen bond donor, acceptor, or both? The pentose sugar contains five carbon atoms. The two main functional groups that are attached to the sugar are often named in reference to the carbon to whch they are bound.
We will often use the carbon number to refer to functional groups on nucleotides so be very familiar with the structure of the pentose sugar.
The difference between the sugars is the presence of the hydroxyl group on the 2' carbon of the ribose and its absence on the 2' carbon of the deoxyribose. You can, therefore, determine if you are looking at a DNA or RNA nucleotide by the presence or absence of the hydroxyl group on the 2' carbon atom—you will likely be asked to do so on numerous occasions, including exams.
There can be anywhere between one and three phosphate groups bound to the 5' carbon of the sugar. The phosphoanhydride bonds between that link the phosphate groups to each other have specific chemical properties that make them good for various biological functions.
The hydrolysis of the bonds between the phosphate groups is thermodynamically exergonic in biological conditions; nature has evolved numerous mechanisms to couple this negative change in free energy to help drive many reactions in the cell. Figure 2 shows the structure of the nucleotide triphosphate Adenosine Triphosphate, ATP, that we will discuss in greater detail in other chapters.
The term "high-energy bond" is used A LOT in biology. This term is, however, a verbal shortcuts that can cause some confusion. The term refers to the amount of negative free energy associated with the hydrolysis of the bond in question. The water or other equivalent reaction partner is an important contributor to the energy calculus.
In ATP, for instance, simply "breaking" a phosphoanhydride bond - say with imaginary molecular tweezers - by pulling off a phosphate would not be energetically favorable. We must, therefore, be careful not to say that breaking bonds in ATP is energetically favorable or that it "releases energy". Rather, we should be more specific, noting that they hydrolysis of the bond is energetically favorable. Some of this common misconception is tied to, in our opinion, the use of the term "high energy bonds".
While in Bis2a we have tried to minimize the use of the vernacular "high energy" when referring to bonds, trying instead to describe biochemical reactions by using more specific terms, as students of biology you will no doubt encounter the potentially misleading - though admittedly useful - short cut "high energy bond" as you continue in your studies.
So, keep the above in mind when you are reading or listening to various discussions in biology. Heck, use the term yourself. Just make sure that you really understand what it refers to. DNA has a double helix structure shown below created by two strands of covalently linked nucleotide subunits.
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