Structure and Roles of Nucleic Acids Flashcards
compare the structure of
RNA and DNA
(Draw a nucleotide using
shapes; recognise (not
draw) the structural
formulae of nucleotides,
ribose, deoxyribose,
pyrimidines, purines;
nature of hydrogen bonds.)
Structure of RNA and DNA:
Nucleotides:
Both RNA and DNA are made up of nucleotides, which are the building blocks of these nucleic acids.
A nucleotide consists of three main components:
A phosphate group (represented as a circle).
A five-carbon sugar molecule:
RNA contains ribose sugar (a pentagon shape).
DNA contains deoxyribose sugar (a pentagon shape with one oxygen atom missing).
A nitrogenous base (represented as a rectangle):
RNA contains the bases adenine (A), cytosine (C), guanine (G), and uracil (U).
DNA contains the bases adenine (A), cytosine (C), guanine (G), and thymine (T).
Backbone:
The backbone of RNA and DNA is formed by the alternating sugar and phosphate groups, connected by phosphodiester bonds (not shown in the diagram).
Hydrogen Bonds:
Hydrogen bonds form between complementary nitrogenous bases in RNA and DNA, stabilizing the structure of the double helix in DNA and RNA secondary structures.
Adenine (A) pairs with uracil (U) in RNA via two hydrogen bonds.
Adenine (A) pairs with thymine (T) in DNA via two hydrogen bonds.
Cytosine (C) pairs with guanine (G) in both RNA and DNA via three hydrogen bonds.
Overall Structure:
RNA molecules are typically single-stranded and can fold into various secondary structures due to intramolecular base pairing and interactions.
DNA molecules are usually double-stranded and form a double helix structure with two antiparallel strands, held together by hydrogen bonds between complementary base pairs.
explain the importance of
hydrogen bonds and base
pairing in DNA replication
(Recognition of the
significance of 5’ and 3’;
semiconservative
replication; genetic code.)
Hydrogen bonds and base pairing play crucial roles in DNA replication, ensuring the accurate transmission of genetic information from one generation to the next. Here’s why they are important:
Maintaining DNA Structure:
Hydrogen bonds between complementary base pairs (adenine-thymine and cytosine-guanine) stabilize the double helix structure of DNA.
Base pairing ensures that the two strands of the DNA molecule remain aligned in an antiparallel orientation, with the 5’ end of one strand matching the 3’ end of the other strand.
Semiconservative Replication:
During DNA replication, each parent DNA strand serves as a template for the synthesis of a new complementary strand.
Hydrogen bonds between complementary bases allow for the accurate copying of genetic information, ensuring that each daughter DNA molecule contains one original (parental) strand and one newly synthesized (daughter) strand.
This process, known as semiconservative replication, ensures the fidelity of DNA replication and the preservation of genetic continuity across generations.
Enzymatic Action:
Enzymes involved in DNA replication, such as DNA polymerases, rely on hydrogen bonding and base pairing to ensure the correct insertion of nucleotides into the growing daughter strand.
DNA polymerases can only add nucleotides to the 3’ end of a growing DNA strand, a process known as DNA synthesis in the 5’ to 3’ direction.
Base pairing between incoming nucleotides and the template strand guides the enzymatic action of DNA polymerases, facilitating the accurate copying of genetic information.
Preserving Genetic Code:
The specific pairing of adenine with thymine and cytosine with guanine during DNA replication ensures the faithful transmission of the genetic code.
Any errors in base pairing or replication fidelity can lead to mutations, which may alter the genetic information encoded in the DNA sequence and potentially affect the phenotype of an organism
describe the roles of DNA
and RNA in protein
synthesis
(Different types of RNA
(tRNA, rRNA and mRNA)
and their respective roles.
Initiation, transcription,
translation, termination)
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) play complementary roles in the process of protein synthesis, which involves the transcription of genetic information from DNA into RNA and the translation of RNA into proteins. Here’s an overview of the roles of DNA and RNA in protein synthesis:
DNA:
DNA serves as the repository of genetic information in the cell, containing the instructions for the synthesis of proteins.
The sequence of nucleotide bases in DNA encodes the sequence of amino acids in proteins, which determines their structure and function.
During protein synthesis, DNA acts as a template for the synthesis of RNA molecules through the process of transcription.
RNA:
RNA molecules are involved in various stages of protein synthesis, including transcription and translation.
There are three main types of RNA involved in protein synthesis:
Messenger RNA (mRNA): Carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm, where it serves as a template for protein synthesis during translation.
Transfer RNA (tRNA): Helps to decode the mRNA sequence and deliver the corresponding amino acids to the ribosome during protein synthesis.
Ribosomal RNA (rRNA): Forms the structural and catalytic core of ribosomes, the cellular organelles responsible for protein synthesis.
Initiation:
Protein synthesis begins with the initiation of transcription in the nucleus, where RNA polymerase binds to the promoter region of a gene on the DNA molecule.
RNA polymerase then synthesizes a complementary RNA strand using one of the DNA strands as a template, resulting in the formation of a pre-mRNA molecule.
Once transcription is initiated, the pre-mRNA molecule undergoes processing, including the removal of introns and splicing of exons to produce mature mRNA.
Transcription:
During transcription, RNA polymerase synthesizes an RNA molecule complementary to one of the DNA strands, using the base-pairing rules (A-U, C-G).
The mRNA molecule carries the genetic information from the DNA in the nucleus to the cytoplasm, where protein synthesis occurs.
Translation:
Translation takes place on ribosomes in the cytoplasm, where mRNA is decoded into a sequence of amino acids to form a polypeptide chain.
The process of translation involves three main steps: initiation, elongation, and termination.
During initiation, the small ribosomal subunit binds to the mRNA molecule, and the initiator tRNA carrying the amino acid methionine binds to the start codon (AUG).
Elongation involves the sequential binding of tRNA molecules carrying amino acids to the mRNA codons on the ribosome, forming peptide bonds between adjacent amino acids.
Termination occurs when a stop codon (UAA, UAG, or UGA) is encountered on the mRNA molecule, leading to the release of the completed polypeptide chain from the ribosome.
explain the relationship
between the sequence of
nucleotides and the amino
acid sequence in a
polypeptide
The relationship between the sequence of nucleotides in DNA or RNA and the amino acid sequence in a polypeptide is central to the process of protein synthesis. This relationship is governed by the genetic code, which specifies how sequences of nucleotides (codons) are translated into sequences of amino acids. Here’s how it works:
Genetic Code:
The genetic code is a set of rules that determines how nucleotide triplets (codons) in mRNA are translated into specific amino acids during protein synthesis.
Each codon consists of three nucleotides, and there are 64 possible codons (4 nucleotides in triplets result in 4^3 = 64 combinations).
Codon-Amino Acid Correspondence:
Each codon in mRNA corresponds to a specific amino acid or a signal for the start or stop of translation.
For example, the codon AUG serves as the start codon, encoding the amino acid methionine and signaling the beginning of protein synthesis.
There are 61 codons that code for amino acids, and three codons (UAA, UAG, UGA) serve as stop codons, signaling the termination of translation.
Reading Frame:
The reading frame refers to the specific way in which nucleotides are grouped into codons during translation.
Reading the mRNA sequence in the correct reading frame is essential for accurate translation of the genetic code into the corresponding amino acid sequence.
tRNA and Amino Acid Attachment:
Transfer RNA (tRNA) molecules serve as adapters between the mRNA codons and the corresponding amino acids.
Each tRNA molecule carries a specific amino acid at one end and has an anticodon at the other end, which base-pairs with the complementary mRNA codon during translation.
Translation:
During translation, ribosomes move along the mRNA molecule, reading the codons in the 5’ to 3’ direction and synthesizing a polypeptide chain based on the sequence of codons.
As each codon is read, the corresponding amino acid is added to the growing polypeptide chain by formation of a peptide bond between adjacent amino acids.
The sequence of codons in the mRNA dictates the sequence of amino acids in the polypeptide chain, determining its primary structure.
Protein Folding and Function:
The sequence of amino acids in the polypeptide chain determines its unique three-dimensional structure through interactions such as hydrogen bonding, disulfide bridges, and hydrophobic interactions.
The three-dimensional structure of a protein is crucial for its function, as it determines how the protein interacts with other molecules and performs its biological roles.
explain the relationship
between the structure of
DNA, protein structure
and the phenotype of an
organism
Structure of RNA and DNA:
Nucleotides:
Both RNA and DNA are made up of nucleotides, which are the building blocks of these nucleic acids.
A nucleotide consists of three main components:
A phosphate group (represented as a circle).
A five-carbon sugar molecule:
RNA contains ribose sugar (a pentagon shape).
DNA contains deoxyribose sugar (a pentagon shape with one oxygen atom missing).
A nitrogenous base (represented as a rectangle):
RNA contains the bases adenine (A), cytosine (C), guanine (G), and uracil (U).
DNA contains the bases adenine (A), cytosine (C), guanine (G), and thymine (T).
Backbone:
The backbone of RNA and DNA is formed by the alternating sugar and phosphate groups, connected by phosphodiester bonds (not shown in the diagram).
Hydrogen Bonds:
Hydrogen bonds form between complementary nitrogenous bases in RNA and DNA, stabilizing the structure of the double helix in DNA and RNA secondary structures.
Adenine (A) pairs with uracil (U) in RNA via two hydrogen bonds.
Adenine (A) pairs with thymine (T) in DNA via two hydrogen bonds.
Cytosine (C) pairs with guanine (G) in both RNA and DNA via three hydrogen bonds.
Overall Structure:
RNA molecules are typically single-stranded and can fold into various secondary structures due to intramolecular base pairing and interactions.
DNA molecules are usually double-stranded and form a double helix structure with two antiparallel strands, held together by hydrogen bonds between complementary base pairs.
