Understandings:
● Transcription occurs in a 5 to 3 direction.
● Nucleosomes help to regulate transcription in eukaryotes.
● Eukaryotic cells modify mRNA after transcription.
● Splicing of mRNA increases the number of different proteins an organism can produce.
● Gene expression is regulated by proteins that bind to specific base sequences in DNA.
● The environment of a cell and of an organism has an impact on gene expression.
Applications and skills:
● Application: The promoter as an example of non-coding DNA with a function.
● Skill: Analysis of changes in the DNA methylation patterns.
Guidance
● RNA polymerase adds the 5 end of the free RNA nucleotide to the 3 end of the growing mRNA molecule.
NATURE OF SCIENCE
Looking for patterns, trends, and discrepancies: there is mounting evidence that the environment can trigger heritable changes in epigenetic factors.
- Is there a central dogma of molecular biology?
DNA → RNA → Protein
The process that occurs at the first arrow in the central dogma is transcription. The process that occurs at the second arrow is translation.
Even though scientists have found exceptions to the central dogma, the basic idea, that genetic information flows in this general direction, has not been invalidated.
- Transcription: DNA → RNA
Transcription has some similarities with replication. For both processes, the double helix must be opened to expose the base sequence of the nucleotides. In replication, helicase unzips the DNA and both strands become templates for the formation of two daughter strands of DNA. However, in transcription, helicase is not involved. Instead, an enzyme called RNA polymerase separates the two DNA strands. The RNA polymerase also allows polymerization of RNA nucleotides as base pairing occurs along the DNA template. To provide these functions, the RNA polymerase must first combine with a region of the DNA strand called a promoter. You will recall that, in DNA replication, DNA polymerase allows assembly only in a 5ʹ to 3ʹ direction. The same is true with RNA polymerase. The 5ʹ ends of free RNA nucleotides are added to the 3ʹ end of the RNA molecule being synthesized.
- But which strand of DNA is copied?
One strand is complementary to the other, so there is a difference in the code of the strands. The codons are specific for certain amino acids or are start or stop messages. The start or stop codons are also known as punctuation codons. The codons are specific for certain amino acids or punctuation signals. Therefore, complementary strands mean different codons, different amino acids, and, finally, different proteins.
The DNA strand that carries the genetic code is called the sense strand (or the coding strand). The other strand is called the antisense strand (or the template strand). The sense strand has the same sequence as the newly transcribed RNA, except with thymine in place of uracil. The antisense strand is the strand that is copied during transcription.
- The terminator
The sections of DNA involved in transcription are:
promoter → transcription unit → terminator
The transcription bubble moves from the DNA promoter region towards the terminator.
The terminator is a sequence of nucleotides that, when transcribed, causes the RNA polymerase to detach from the DNA. When this happens, transcription stops and the RNA transcript is detached from the DNA. The transcript carries the code of the DNA and is referred to as messenger RNA (mRNA).
- Proteins and gene expression
In many cases, gene expression is also regulated by proteins. Every cell appears to have many different types of transcription factors. These are proteins that regulate transcription by assisting the binding of RNA polymerase at the promoter region
of a gene. Another type of protein that has an effect on gene expression is called a transcription activator. Transcription activators cause looping of DNA, which results in a shorter distance between the activator and the promoter region of the gene.
This will bring about gene expression. There are also repressor proteins that bind to segments of DNA called silencers. This prevents transcription of the segment of that particular region.
● Transcription occurs in a 5 to 3 direction.
● Nucleosomes help to regulate transcription in eukaryotes.
● Eukaryotic cells modify mRNA after transcription.
● Splicing of mRNA increases the number of different proteins an organism can produce.
● Gene expression is regulated by proteins that bind to specific base sequences in DNA.
● The environment of a cell and of an organism has an impact on gene expression.
Applications and skills:
● Application: The promoter as an example of non-coding DNA with a function.
● Skill: Analysis of changes in the DNA methylation patterns.
Guidance
● RNA polymerase adds the 5 end of the free RNA nucleotide to the 3 end of the growing mRNA molecule.
NATURE OF SCIENCE
Looking for patterns, trends, and discrepancies: there is mounting evidence that the environment can trigger heritable changes in epigenetic factors.
- Is there a central dogma of molecular biology?
DNA → RNA → Protein
The process that occurs at the first arrow in the central dogma is transcription. The process that occurs at the second arrow is translation.
Even though scientists have found exceptions to the central dogma, the basic idea, that genetic information flows in this general direction, has not been invalidated.
- Transcription: DNA → RNA
Transcription has some similarities with replication. For both processes, the double helix must be opened to expose the base sequence of the nucleotides. In replication, helicase unzips the DNA and both strands become templates for the formation of two daughter strands of DNA. However, in transcription, helicase is not involved. Instead, an enzyme called RNA polymerase separates the two DNA strands. The RNA polymerase also allows polymerization of RNA nucleotides as base pairing occurs along the DNA template. To provide these functions, the RNA polymerase must first combine with a region of the DNA strand called a promoter. You will recall that, in DNA replication, DNA polymerase allows assembly only in a 5ʹ to 3ʹ direction. The same is true with RNA polymerase. The 5ʹ ends of free RNA nucleotides are added to the 3ʹ end of the RNA molecule being synthesized.
- But which strand of DNA is copied?
One strand is complementary to the other, so there is a difference in the code of the strands. The codons are specific for certain amino acids or are start or stop messages. The start or stop codons are also known as punctuation codons. The codons are specific for certain amino acids or punctuation signals. Therefore, complementary strands mean different codons, different amino acids, and, finally, different proteins.
The DNA strand that carries the genetic code is called the sense strand (or the coding strand). The other strand is called the antisense strand (or the template strand). The sense strand has the same sequence as the newly transcribed RNA, except with thymine in place of uracil. The antisense strand is the strand that is copied during transcription.
- The terminator
The sections of DNA involved in transcription are:
promoter → transcription unit → terminator
The transcription bubble moves from the DNA promoter region towards the terminator.
The terminator is a sequence of nucleotides that, when transcribed, causes the RNA polymerase to detach from the DNA. When this happens, transcription stops and the RNA transcript is detached from the DNA. The transcript carries the code of the DNA and is referred to as messenger RNA (mRNA).
- Proteins and gene expression
In many cases, gene expression is also regulated by proteins. Every cell appears to have many different types of transcription factors. These are proteins that regulate transcription by assisting the binding of RNA polymerase at the promoter region
of a gene. Another type of protein that has an effect on gene expression is called a transcription activator. Transcription activators cause looping of DNA, which results in a shorter distance between the activator and the promoter region of the gene.
This will bring about gene expression. There are also repressor proteins that bind to segments of DNA called silencers. This prevents transcription of the segment of that particular region.