3.4.1 3.1.5 Nucleic acids are important information-carrying molecules Flashcards
3.1.5 What is DNA: structure, purpose, draw structure.
What-DNA is the hereditary material- a polynucleotide
Where-In eukaryotes – found in the nucleus
Important-Passes on genetic information from cell to cell & generation to generation
Structure-DNA consists of two strands, arranged in a double helix. These strands are made up of subunits called nucleotides. Each nucleotide contains a phosphate, a 5-carbon sugar molecule and a nitrogenous base.
Function-DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism
3.1.5 What is RNA: structure, purpose, draw structure.
Structure: Ribonucleic acid is a polymer made up of nucleotides. It is a single, relatively short, polynucleotide chain in which the pentose sugar is always ribose and the organic bases are adenine, guanine, cytosine and uracil (Figure 2).
Purpose(s)One type of RNA transfers genetic information from DNA to the ribosomes. The ribosomes themselves arc made up of proteins and another type of RNA. A third type of RNA is involved in protein synthesis.
(Complex)Messenger RNA (mRNA) copies portions of genetic code, a process called transcription, and transports these copies to ribosomes, which are the cellular factories that facilitate the production of proteins from this code.
Transfer RNA (tRNA) is responsible for bringing amino acids, basic protein building blocks, to these protein factories, in response to the coded instructions introduced by the mRNA. This protein-building process is called translation.
Finally, Ribosomal RNA (rRNA) is a component of the ribosome factory itself without which protein production would not occur.
3.1.5 Compare and contrast features of RNA and DNA
DNA- Holds genetic information RNA- Carries genetic info from DNA to ribosomes DNA- Thymine Both- Adenine DNA- Deoxyribose sugar Both- Cytosine RNA- Uracil Both- Phosphate Both- Nucleic acid DNA- Double stranded RNA- Single stranded
3.1.5 What is a nucleotide? How do the three components join? Draw structure
A pentose sugar, phosphate group and organic base joined, as a result of condensation reactions.
3.1.5 How is a polynucleotide formed?
The pentose sugar, phosphate group and organic base are joined, as a result of condensation reactions, to form a single nucleotide (mononucleotide)
Two mononucleotides may, in turn, be joined as a result of a condensation reaction between the deoxyribose sugar of one mononucleotide and the phosphate group of another. The bond formed between them is called a phosphodiester bond The new structure is called a dinucleotide.
The continued linking of mononucleotides in this way forms a long chain known as a polynucleotide
3.1.5 What is CHARGRAFF’s RULE? Why does it work?
states that DNA base pairs are always adenine with thymine (A-T) and cytosine with guanine (C-G). A purine always pairs with a pyrimidine and vice versa. However, A doesn’t pair with C, despite that being a purine and a pyrimidine.
This rule is named after the scientist Erwin Chargaff who discovered that there are essentially equal concentrations of adenine and thymine as well as guanine and cytosine within almost all DNA molecules. These ratios can vary between organisms, but the actual concentrations of A are always essentially equal to T and same with G and C.
To do both with the hydrogen bonding that joins the complementary DNA strands along with the available space between the two strands.
-There are about 20 Å (angstroms, where one angstrom is equal to 10-10 meters) between two complementary strands of DNA. Two purines and two pyrimidines together would simply take up too much space to be able to fit in the space between the two strands. This is why A cannot bond with G and C cannot bond with T.
But why can’t you swap which purine bonds with which pyrimidine? The answer has to do with hydrogen bonding that connects the bases and stabilizes the DNA molecule. The only pairs that can create hydrogen bonds in that space are adenine with thymine and cytosine with guanine. A and T form two hydrogen bonds while C and G form three. It’s these hydrogen bonds that join the two strands and stabilize the molecule, which allows it to form the ladder-like double helix.
3.1.5 Purines and pyrimidines
Purines are larger than pyrimidines because they have a two-ring structure while pyrimidines only have a single ring.
Purines- A + T
Pyrimidines- C+G+U
3.1.5 Stability of DNA- bonds involved
1) Phosphodiester bond- Sugar-phosphate backbone on the outside of the structure
Protects chemically reactive nitrogenous bases
2)Hydrogen bonds- 3 H-bonds form between C and G. If more C-G bonds are present, the helix is more stable.
3.1.5 Explain why the helical structure of DNA is advantageous to the hereditary nature of DNA
Makes DNA molecule more compact
Stores more information
Protects chemical bases
Easily replicated
3.1.5 Forming nucleotides (in depth)
Nucleotides linked into a single strand via a condensation reaction
The phosphate group (attached to the 5’-C of the sugar) joins with the hydroxyl (OH) group attached to the 3’-C of the sugar
This forms a phosphodiester bond between the two nucleotides and forms a molecule of H2O
Two polynucleotide chains of DNA are held together by hydrogen bonds between complementary base pairs
3.1.5 Further reading
https: //www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397/
https: //sciencing.com/complementary-base-pairing-rule-8728565.html
3.1.5 How is DNA adapted for function?
- It is a very stable structure which normall y passes from generation to generation without change. Only rar ly does it mutate.
- Its two separate strands are joined only with hydrogen bonds, which allow them to separate during DNA replication (Topic 2.2) and protein synthesis.
- It is an extremely large molecule and therefore carries an immense amount of genetic information.
- By having the base pairs within the helical cylinder of the deoxyribose-phosphare backbone, the genetic information is to some extent protected from being corrupted by outside chemical and physical forces.
- Base pairing leads to DNA being able to replicate and to transfer information as mRNA.
Important definitions: Genome: Proteome:
Genome: Complete set of genes in a cell
Proteome: Full range of proteins that a cell is able to produce
Eukaryotic DNA organisation
Gets even more coiled so can be stored in small nucleus, so is compact
1- DNA bases hydrogen bonded together – join two polynucleotide strands
2-One DNA strand made up of nucleotides joined via phosphodiester bonds
3-DNA molecule twists into a double helix structure
4-DNA wraps around histone proteins
5-Nucleosomes coil into thin chromatin fibre
6-Further condensation of chromatin
7-Homologous chromosome
Humans have ______ chromosomes in every cell in the body (except _________________________). A __________________ pair of chromosomes carry the same ________ but are not identical. This is because the chromosomes can carry different versions of the same gene, called _________.
46
sperm and eggs
homologous
genes
alleles
Eukaryotes vs Prokaryotes
Length E-Long P-Short
Associated with proteins? -E-Wrapped around histones P- No
Linear? E- Yes P- Circular
Structure formed E- Chromosomes P- Chromosomal DNA Loop
Endosymbiotic theory and evience
The endosymbiotic theory states that some of the organelles in today’s eukaryotic cells were once prokaryotic microbes.
The first eukaryotic cell engulfed other prokaryotes and instead of being digested, they lived as symbionts. Other words- Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship.
Mitochondria formed when bacteria capable of aerobic respiration were ingested; ANCESTOR HETERTROPHIC EUKARYOTE
Chloroplasts formed when photosynthetic bacteria were ingested: ANCESTOR AUTOTROPHIC CELL
They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell.
Mitochondria and chloroplasts cannot grow outside their host cell.
Evidence for this is based on the following:
Chloroplasts are the same size as prokaryotic cells, divide by binary fission, and, like bacteria, have Fts proteins at their division plane. The mitochondria are the same size as prokaryotic cells, divide by binary fission, and the mitochondria of some protists have Fts homologs at their division plane.
Mitochondria and chloroplasts have their own DNA that is circular, not linear.
Mitochondria and chloroplasts have their own ribosomes that have 30S and 50S subunits, not 40S and 60S.
Several more primitive eukaryotic microbes, such as Giardia and Trichomonas have a nuclear membrane but no mitochondria.
Although evidence is less convincing, it is also possible that flagella and cilia may have come from spirochetes.
