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Structure and function of nucleic acids
This is a mind map about the structure and function of nucleic acids. Nucleic acids are biological macromolecules with nucleic acid as the basic unit, which carry and transmit genetic information.
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Structure and function of nucleic acids
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Structure and function of nucleic acids
Chemical composition and primary structure of nucleic acids
Nucleic acid is a biological macromolecule with nucleotides as its basic unit, which carries and transmits genetic information.
DNA exists in the nucleus and mitochondria, carrying genetic information and passing it on to generations through replication.
RNA is found in the cytoplasm, nucleus and mitochondria
Complete hydrolysis of nucleotides releases equimolar amounts of the base pentose sugar and phosphate
Nucleotides and deoxynucleotides are the basic building blocks of nucleic acids
Bases are one of the basic components of nucleotides. Bases are nitrogen-containing heterocyclic compounds.
Adenine, guanine and cytosine are common to DNA and RNA. Thymine is specific to DNA and uracil is specific to RNA
Ribose is another basic component of nucleotides. Ribose is found in RNA, while deoxyribose is found in DNA. The chemical stability of deoxyribose is better than that of ribose.
The product of the condensation reaction between the nucleotide base and ribose. The C-1' atom of ribose and the N-9 atom of purine or the N-1 atom of pyrimidine form a β-N glycosidic bond through a condensation reaction.
Nucleotides exist in the form of other derivatives and are involved in the regulation of metabolism of various substances and the regulation of protein functions.
Cyclic AMP and Cyclic GMP are second messengers in the signal transduction process and have the function of regulating gene expression.
Coenzyme I (nicotinamide adenine dinucleotide), coenzyme II (nicotinamide adenine dinucleotide phosphate), flavin adenine nucleotide. They are important components of biological oxidation systems and play an important role in the process of transferring electrons or protons.
6-mercaptopurine, cytarabine and 5-fluorouracil are all derivatives of bases, which can exert anti-tumor effects by interfering with the nucleotide metabolism of tumor cells and inhibiting nucleic acid synthesis.
DNA is a linear macromolecule formed by the polymerization of deoxyribonucleotides through 3', 5'-phosphodiester bonds.
DNA is a linear macromolecule composed of multiple deoxyribonucleotides. The deoxyribonucleotides are covalently connected through 3', 5'-phosphodiester bonds.
Backbone: Alternating phosphate groups and pentose sugars form the backbone of DNA
Multiple deoxyribonucleotides form a directional linear molecule through phosphodiester bonds
A polydeoxynucleotide chain can only be extended from its 3'-end
RNA is a linear macromolecule formed by the polymerization of ribonucleotides through 3', 5'-phosphodiester bonds.
RNA is a linear macromolecule formed by connecting multiple nucleotide molecules through 3', 5'-phosphodiester bonds under the catalysis of RNA polymerase, and also has 5'-3' directionality.
The difference between DNA and RNA
1The pentose sugar of RNA is still ribose, not deoxyribose
2The pyrimidines of RNA are cytosine and uracil
The primary structure of nucleic acids is the sequence of nucleotides
Primary structure: The arrangement of RNA nucleotides and DNA deoxynucleotides from 5'-end to 3'-end is defined as the primary structure of nucleic acid.
The only difference between nucleotides is the base, so the primary structure of a nucleic acid is its base sequence
The size of a nucleic acid molecule is often expressed by the number of nucleotides or the number of base pairs.
Fragments of nucleic acids shorter than 50 nucleotides are often called oligonucleotides
DNA spatial structure and function
The functional groups on the DNA chain can produce special hydrogen bonds, ionic forces, hydrophobic forces and steric hindrance effects, etc., so that the atoms of the DNA molecule have a certain relative position relationship in the three-dimensional space. This is called DNA the spatial structure of
The secondary structure of DNA is a double helix
Experimental basis of DNA double helix structure
Chargaff's rule for the four bases in DNA
1The DNA base composition of different biological individuals is different.
2The DNA of different organs or tissues of the same individual has the same base composition
3. The DNA and base components of a specific tissue do not change with its age, nutritional status and environment.
4 For a given organism, the number of moles of adenine is equal to the number of moles of thymine, and the number of moles of guanine is equal to the moles of cytosine.
The significance of the discovery of DNA double helix structure
1 explains the molecular mechanism by which genetic traits are passed from generation to generation in the biological world, laying the foundation for modern life sciences.
2 Reveals the material nature of DNA as a carrier of genetic information
3 Provides a structural basis for DNA as a replication template and gene transcription template
4 laid the experimental foundation for molecular biology and modern genetic engineering
Key points of the DNA double helix structure model
DNA is composed of two polydeoxynucleotide strands
Both chains are along the 5'-3' direction, one is from top to bottom, and the other is from bottom to top, showing anti-parallel
complementary base pairs formed between two polydeoxynucleotide strands of DNA
The chemical structural characteristics of the base determine the unique interaction between the two chains
Adenine on one chain forms two pairs of hydrogen bonds with thymine on the other chain
Guanine on one strand forms three pairs of hydrogen bonds with cytosine on the other strand
This specific interaction between bases is called a complementary base pair The two strands of DNA are called complementary strands
The hydrophilic backbone of the two polydeoxynucleotide strands embeds the complementary base pairs within the DNA double helix
The deoxyribose and phosphate groups of the polydeoxyribonucleotide chain form a hydrophilic backbone on the outside of the double helix, while the hydrophobic base pairs are embedded on the inside of the double helix.
Reason: The antiparallel direction of the DNA double strands makes the connection between the base pairs and the phosphate backbone asymmetrical
Result: A major groove and a minor groove are produced on the surface of the DNA double helix structure
Two base pair planes overlap, resulting in base stacking
Two adjacent base pair planes overlap each other, resulting in hydrophobic base stacking forces
Diversity of DNA double helix structure
Changes in the ionic strength or relative humidity of the solution can cause changes in the grooves, pitch, rotation angle, base pair inclination, etc. of the DNA double helix structure.
The natural double helix structure is divided into A type, B type, and Z type.
DNA multi-stranded structure
The formation of Hoogsteen hydrogen bonds does not destroy the Wasson-Crick hydrogen bonds in the original base pairs.
The 3'-end of eukaryotic chromosomes is a highly repetitive GT-rich single strand called a telomere
As a single-stranded structure, telomeres have great flexibility and can fold back on themselves to form a special structure called G-quadruplex.
DNA double strands are coiled and folded to form a dense higher-order structure
The linear DNA double strand is not a rigid molecule and has a certain degree of flexibility.
When the coiling direction is the same as the double helix direction of the DNA double, the superhelical structure is a positive supercoil, otherwise it is a negative supercoil.
Closed circular DNA has a superhelical structure
The DNA of most prokaryotes is a circular double helix molecule
In bacterial DNA, different DNA regions can have different degrees of superhelical structures, and superhelical structures can exist independently of each other.
Mitochondria and chloroplasts are organelles containing extranuclear genetic material in eukaryotic cells. Mitochondrial DNA also has a closed circular double helix structure.
Mitochondrial DNA is the genetic material outside the nucleus of eukaryotic cells
Eukaryotic DNA is assembled into higher-order structures step by step
During most of the cell cycle, the DNA in the nucleus exists as loose chromatin. Only during cell division does the DNA in the nucleus form highly dense chromosomes.
The basic unit of chromatin is the nucleosome
Eukaryotic chromosomes have two functional regions: telomeres and centromeres
Telomeres are enlarged granular structures at the ends of chromosomes, which are composed of DNA and DNA-binding proteins at the ends of chromosomes.
Telomeres play an important role in maintaining the stability of chromosome structure and maintaining the integrity of DNA during replication.
Centromere is the junction point of two chromatids
DNA is the main genetic material
DNA is the carrier of genetic information of organisms and provides a template for gene replication and transcription. It is the material basis of life inheritance and the information basis of individual life activities.
The nucleotide sequence of DNA determines the sequence of amino acids in proteins in the form of genetic code.
DNA has the characteristics of high stability and is used to maintain the relative stability of the genetic characteristics of biological systems.
DNA also exhibits a high degree of complexity and can undergo various recombinations and mutations to adapt to changes in the environment.
The genetic information of organisms exists in the form of genes
Genes are DNA segments encoding RNA or polypeptide chains and specific nucleotide sequences in DNA. They provide templates for DNA replication and RNA biosynthesis.
The genome of an organism refers to all the genetic information contained in the organism's DNA, that is, the complete nucleotide sequence in a set of chromosomes
Physical and chemical properties of nucleic acids
Nucleic acids have strong UV absorption
Purines and pyrimidines are heterocyclic molecules containing conjugated double bonds
Bases, nucleosides, nucleotides and nucleic acids have their maximum absorption values near 260m under neutral conditions, which is determined by the conjugated double bonds of the bases
Nucleic acids are polybasic acids with strong acidity. The length of RNA is much smaller than that of DNA. DNA macromolecules are prone to breakage under the action of mechanical force.
Nucleic acid molecules in solution can precipitate in a gravitational field. In the gravitational field formed by ultracentrifugation, the sedimentation rates of nucleic acid molecules with different conformations are greatly different.
DNA denaturation is the process of dissociation of one DNA double strand into two DNA single strands
Certain extreme physical and chemical conditions can break the hydrogen bonds between complementary base pairs of DNA double strands and destroy the base stacking force, causing one DNA double strand to dissociate into two single strands. This phenomenon is called DNA denaturation
The essence of DNA denaturation is the breakage of hydrogen bonds between double strands
Color enhancement effect: During the unzipping process of DNA, more bases embedded in the double helix structure are exposed, so the absorbance of the solution containing DNA at 260nm increases.
When the change in UV absorbance reaches half of the maximum change value, the corresponding temperature is defined as the melting temperature of DNA
Denatured nucleic acids can renature or form hybrid double strands
Renaturation: After slowly removing the denaturing conditions, the two dissociated DNA complementary strands can re-pair to form DNA double strands and restore the original double helix structure.
Thermal denatured DNA can be renatured after slow cooling, a process called annealing
Why cool slowly? If the thermally denatured DNA is cooled quickly, the two dissociated complementary strands will not have time to form double strands, so the DNA cannot be renatured.
As long as there is a certain degree of base complementarity between the two nucleic acid single strands, they may form hybrid double strands.
Nucleic acid molecular hybridization technology is widely used to study the positioning of DNA fragments in the genome, identify sequence similarities between nucleic acid molecules, and detect the presence or absence of target genes in samples to be tested.
RNA spatial structure and function
RNA can be divided into
coding RNA
non-coding RNA
One category is RNA that ensures the realization of basic biological functions, including transfer RNA, ribosomal RNA, and RNA signal recognition particles.
One type is regulatory non-coding RNA
mRNA is the template for protein biosynthesis
RNA has been shown to be a product synthesized in the nucleus using DNA as a template
mRNA has the smallest abundance, the most types, and the shortest lifespan
The newly generated primary product of mRNA in the nucleus is called nuclear heterogeneous RNA and contains introns and exons.
lnRNA is capped, tailed, and spliced into mature mRNA
The 5'-end capped structure of eukaryotic cell mRNA
The 5'-cap structure of eukaryotic mRNA can be associated with a class of proteins called cap tubercle proteins. This complex helps maintain the stability of mRNA, coordinates the transport of mRNA from the nucleus to the cytoplasm, and promotes the binding of ribosomes and translation initiation factors in protein biosynthesis.
The structure of the 3'-terminal polyadenylase tail of eukaryotic and some prokaryotic mRNAs
The poly-tail structure binds to the poly-binding protein. This 3'-poly tail structure and the 5'-cap structure are jointly responsible for
1Transport of mRNA from nucleus to cytoplasm
2Maintain the stability of mRNA
3 Regulation of translation initiation
hnRNA in eukaryotic cell nuclei undergoes a series of modifications and splicing to become mature mRNA
Exons are the sequence segments that make up mRNA, while introns are non-coding sequences
During the transfer of hnRNA to the cytoplasm, introns are spliced out and exons are joined together. After capping and tailing modifications, hnRNA becomes mature mRNA
The nucleotide sequence of the mRNA determines the amino acid sequence of the protein
Starting from this AUG, every three consecutive nucleotides form a genetic code. Each codon codes for an amino acid until the stop codon consisting of three nucleotides (UAA, UAG or UGA)
The region bounded by the start codon and stop codon is defined as the coding region of mRNA, also called the open reading frame
This region is the nucleotide sequence encoding a protein polypeptide chain
tRNA is the carrier of amino acids in protein synthesis
Transfer RNA serves as a substrate for protein synthesis – the carrier of amino acids participates in protein synthesis and provides activated amino acids for the polypeptide chain being synthesized. tRNA has a stable spatial structure.
tRNA contains a variety of rare bases
Minimum molecular weight
Rare bases refer to some bases other than A, G, C, and U, including dihydrouracil, pseudouracil nucleosides, and methylated purines.
The rare bases in tRNA molecules are modified post-transcriptionally.
tRNA has a specific spatial structure
Specific spatial structure refers to local double strands
The nucleotide sequences between these local double helix structures cannot form complementary base pairs and bulge to form a ring or loop-like structure.
The secondary structure of tRNA exhibits a clover-like shape
All tRNAs have a similar inverted L-shaped spatial structure
The 3'-end of tRNA is always CCA
The 3'-end of tRNA is connected to amino acids
Only amino acids linked to tRNA can participate in protein biosynthesis
The type of amino acid carried by tRNA is determined by the anticodon of tRNA
The anticodon of tRNA can recognize the codon of mRNA
The combination of codons and anticodons enables tRNA to transport the correct amino acids and participate in the synthesis of protein polypeptide chains.
Ribosomes, with rRNA as the main component, are the site of protein synthesis
Ribosomal RNA is the most abundant RNA in cells
rRNA has definite species and conserved nucleotide sequences
rRNA and ribosomal proteins together form ribosomes, which provide the necessary place for protein biosynthesis.
Constitutive non-coding RNA is a key factor in ensuring the transmission of genetic information
catalytic small RNA
also called ribozymes
It has the activity of catalyzing the degradation of specific RNA and plays an important role in splicing modification after RNA synthesis.
nucleolar small RNA
Mainly involved in rRNA processing
nuclear small RNA
Identify the junction between exons and introns on hnRNA and remove the introns
cytoplasmic small RNA
Exists in the cytoplasm, combines with proteins to form a complex, and then exerts biological functions
Regulatory non-coding RNA is involved in the regulation of base expression
Regulatory non-coding RNAs are divided into small non-coding RNAs, long non-coding RNAs and circular RNAs according to their size.
Role: Transcriptional regulation of RNA shearing and modification, translation of mRNA, protein stabilization and transport, chromosome formation and structural stability
Non-coding RNAs are involved in basic life activities such as embryonic development, tissue differentiation, signal transduction, and organ formation, as well as in the occurrence and development of diseases.
Characteristics and functions of small non-coding RNAs
Non-coding small RNAs include microRNAs, interfering small RNAs and piRNAs
MicroRNA regulates gene expression at the post-transcriptional level, mainly by downregulating the expression of target genes through two mechanisms (the choice of the two mechanisms mainly depends on the degree of complementarity between the miRNA and the target gene's mRNA sequence)
miRNA is also involved in various processes such as cell growth, differentiation, senescence, apoptosis, autotropism, migration, and invasion.
Characteristics and functions of long noncoding RNAs
lncRNA is transcribed and generated by RNA polymerase II. After shearing and processing, it forms a structure similar to mRNA.
Characteristics and functions of circular RNA
Circular RNA is a special type of RNA molecule. Different from traditional linear RNA, circRNA molecules form a closed ring structure and have no 5'-end and 3'-end. Therefore, they are not affected by RNA exonucleases and their expression More stable and less likely to degrade
circRNA has a high degree of sequence conservation and has certain tissue, timing and disease specificity.