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Aso Jabar 2024 Molecular biology
2
Molecular biology
Mr: Aso Jabar
2024
Cells can accurately replicate their DNA
A schematic shows a double-stranded DNA molecule undergoing a replication process. On the right, the double helix is opened and the top strand is detached from the bottom. A yellow spherical structure, representing a helicase protein, is bound to the ends of multiple nitrogen bases on the downstream strand.
Replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules. DNA replication is one of the most basic processes that occurs within a cell. Each time a cell divides, the resulting two daughter cells must contain exactly the same genetic information, or DNA, as the parent cell. To accomplish this, each strand of existing DNA serves as a template for replication.
DAN replication
How are DNA strands replicated?
A map shows a region of horizontal single-stranded DNA. A transparent blue spherical structure, representing the enzyme DNA polymerase, binds to a region seven nucleotides long on the right side of the DNA strand. The DNA region bound by DNA polymerase within the transparent enzyme is visible at higher magnification. Six nucleotides in this region are linked by six complementary nucleotides arranged above and parallel to the single strand forming red–green or blue–orange pairs. About two dozen individual nucleotides float in the background.
DNA polymerase
After the primer is in place on the single strand of the uncut polynucleotide, the DNA polymerase wraps itself around that strand and attaches the new nucleotide to the exposed nitrogenous bases. The polymerase thus assembles a new DNA strand onto the existing one (Figure 3).
Each individual nucleotide is represented as a long, rectangular colored rectangle (a nitrogenous base) connected at one end to a gray horizontal column (a sugar molecule).
nitrogenous
A schematic shows a double-stranded DNA molecule undergoing a replication process. The left side of the molecule is double-stranded. In the middle of the molecule, a yellow spherical structure, representing a helicase protein, is attached to the ends of several nitrogen bases on the lower strand. To the right of the helicase protein, the double helix is open and the top strand is separated from the bottom. On the right, a short section of the newly replicated double-stranded DNA molecule is visible.
What triggers replication?
A red spherical molecule, representing the enzyme primase, binds to the bottom strand of DNA on the right side of the helicase.
1
While the helicase and initiator protein (not shown) separate the two polynucleotide sequences, the primase (red) assembles a primer.
2
How is DNA replicated?
Replication occurs in three main steps: double helix opening and separation of DNA strands, template strand priming, and assembly of new DNA segments. During dissociation, the two strands of the DNA double helix are pulled back at a specific location called the origin. Multiple enzymes and proteins then work together to prepare, or prime, the strands for replication. Finally, a special enzyme called DNA polymerase regulates the synthesis of new DNA strands. The following description of this three-stage process applies generally to all cells, but specific variations within the process may occur depending on the organism and cell type.
During dissociation, the two strands of the DNA double helix are pulled back at a specific location called the origin.
A
Multiple enzymes and proteins then work together to prepare, or prime, the strands for replication.
B
translation
Were you ever going to write something down?
A colorful person left a message in your voicemail, and you had to write it down on paper. or colored in class wrote notes, with written agreement to help with.
Transcription of a gene in the next three phases: initiation, continuation, and termination. Here, we briefly see how these steps occur in bacteria. Find out more about the details of each stage (and about how Euroti transliteration is different) in the chapter stages of transcribing.
begin
begin. RNA polyrase binds to a string of DNA called a promoter, which is found near the beginning of a gene. Each class (they are a set of transcribed genes, in bacteria) has its own professor. Once you bind it, RNA polymerase makes separate DNA strands, single-stranded kelp needed to provide for transcription.
The promoter region is transcribed before ( and slightly overlaps) the region that specifies its transcription. Site includes RNA or protein polymerase recognition to bind to.
The promoter region
The DNA is unwound in the promoter region so that RNA polymerase can begin transcription.
DNA
Extension. A single strand of DNA, the template strand, serves as a template for RNA polymerase. “Reading” this template one base at a time, the polymerase synthesizes an RNA molecule from complementary nucleotides, creating a chain that grows from 5′ to 3′. The translation of the RNA itself is the central strand-hook (coding) of the stored DNA, replacing the thymine (T) with the basic uracil (U).
Extension
RNA polymerase
RNA polymerase generates an RNA transcript complementary to the DNA template strand in the 5′ to 3′ direction. Running along the template strand in the direction with 3′ to 5′, the novel double helix of DNA is wash.
The synthesized RNA is only briefly bound to the template array and the strand, the tarwas as a mistake exits the polyrase heraw gives the DNA to unwind and form two licks.
The synthesized RNA
The final termination. The so-called terminator sequences signal that RNA transcription is complete. When transcribed, they cause the transcript to exit the RNA polymerase. An example of a termination mechanism involving hairpin formation in RNA is shown below.
The terminal DNA encodes an RNA region that forms a hairpin structure followed by a string of U nucleotides. The hairpin structure of the transcript causes RNA polymerase to stall. U nucleotides following hairpin formation bind weakly with A nucleotides of the DNA template, allowing the transcript to detach from the template and terminate transcription.
The final termination
In bacteria, RNA transcripts can immediately function as messenger RNA (mRNA). In eukaryotes, the transcript of a protein-coding gene is called pre-mRNA and must undergo additional processing before it can be translated directly.
Eukaryotic RNA modifications
Not all genes are constantly transcribed.
Transcription occurs for individual genes
Not all genes are constantly transcribed. Instead, transcription is controlled individually for each gene (or, in bacteria, for small groups of genes that are transcribed together). Cells carefully regulate transcription, transcribe only those genes whose products are needed at a given moment.
transcription
Transcription is an essential step in using the information from genes in our DNA to make proteins. Proteins are the key molecules that give cells structure and keep them running. Blocking transcription with mushroom toxin causes liver failure and death, because no new RNAs—and thus, no new proteins—can be made.
Transcription is essential to life, and understanding how it works is important to human health. Let's take a closer look at what happens during transcription.
An overview of transcription
An overview of transcription
Transcription is the first step in gene expression. In this process, the DNA sequence of a gene is copied into RNA.
Before transcription can occur, the DNA double helix must unwind near the gene about to be transcribed. The resulting DNA region is called a transcription bubble.
In transcription, a region of DNA is opened. One strand, the template strand, serves as a template for the synthesis of a complementary RNA transcript.
example:1
coding strand: 5′-ATGATCTCGTAA-3′ template strand: 3′-TACTAGAGCATT-5′ RNA transcription: 5′-AUGAUCUCGUAA-3′
In translation, RNA transcripts are read to produce polypeptides.
example: 1
example:2
RNA translation: 5'-AUG AUC UCG UAA-3' Polypeptide: (N-terminal) Met - Ile - Ser - [STOP] (C-terminal)
example: 2
RNA polymerase
RNA polymerases are enzymes that transcribe DNA into RNA. Using a DNA template, RNA polymerase builds a new RNA molecule through base pairing. For instance, if there is a G in the DNA template, RNA polymerase will add a C to the new, growing RNA strand.
RNA polymerase
RNA polymerase always builds a new RNA strand in the 5' to 3' direction. That is, it can only add RNA nucleotides (A, U, C, or G) to the 3' end of the strand.
A
RNA polymerases are large enzymes with multiple subunits, even in simple organisms such as bacteria. Humans and other eukaryotes have three different types of RNA polymerase: I, II, and III. Each specializes in transcribing certain classes of genes. Plants have an additional two kinds of RNA polymerase, IV and V, which are involved in the synthesis of certain small RNAs.
B
Promoters in bacteria
Promoters in bacteria
To get a better sense of how a promoter works, let's look an example from bacteria. A typical bacterial promoter contains two important DNA sequences, the and elements.
RNA polymerase recognizes and binds directly to these sequences. The sequences position the polymerase in the right spot to start transcribing a target gene, and they also make sure it's pointing in the right direction.
The promoter is located at the beginning of the transcribed region, overlaps the preceding DNA, and slightly overlaps with the transcription start site. The promoter contains two elements, the −35 element and the −10 element. Element -35 is centered approximately 35 nucleotides upstream (before) the transcription start site (+1), whereas element -10 is centered approximately 10 nucleotides before the transcription start site.
beginning
In this particular example, the sequence of element −35 (on the coding strand) is 5′-TTGACG-3′, whereas the sequence of element −10 (on the coding strand) is 5′-TATAAT-3′. RNA polymerase has regions that bind specifically to elements −10 and −35.