1. What is cell differentiation and what are different types/levels?
Cell differentiation generally occurs without changes in the nucleotide sequence of a cell’s
genome.
1. Many processes are common to all cells, and any two cells in a single organism therefore
have many gene products in common. These include the structural proteins of
chromosomes, RNA and DNA polymerases, DNA repair enzymes, ribosomal proteins and
RNAs, the enzymes that catalyze the central reactions of metabolism, and many of the
proteins that form the cytoskeleton such as actin
2. Some RNAs and proteins are abundant in the specialized cells in which they function and
cannot be detected elsewhere, even by sensitive tests. Hemoglobin, for example, is
expressed specifically in red blood cells
3. When the patterns of RNA expression in different human cell lines are compared, the level of
expression of almost every gene is found to vary from one cell type to another.
Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to
Protein
A cell can control the proteins it makes by:
(1) controlling when and how often a given gene is transcribed (transcriptional control),
(2) controlling the splicing and processing of RNA transcripts (RNA processing control),
(3) selecting which completed mRNAs are exported from the nucleus to the cytosol and
determining where in the cytosol they are localized (RNA transport and localization control)
(4) selecting which mRNAs in the cytoplasm are translated by ribosomes (translational
control)
(5) selectively destabilizing certain mRNA molecules in the cytoplasm (mRNA degradation
control).
(6) selectively activating, inactivating, degrading, or localizing specific protein molecules after
they have been made (protein activity control). The regulation of protein activity, occurs
largely through covalent post-translational modifications including phosphorylation,
acetylation, and ubiquitylation.
, Summary:
The genome of a cell contains in its DNA sequence the information to make many thousands
of different protein and RNA molecules. A cell typically expresses only a fraction of its genes,
and the different types of cells in multicellular organisms arise because different sets of
genes are expressed. Moreover, cells can change the pattern of genes they express in
response to changes in their environment, such as signals from other cells. Although all of
the steps involved in expressing a gene can in principle be regulated, for most genes the
initiation of RNA transcription provides the most important point of control.
Transcription:
Transcription regulators recognize short stretches of double-helical DNA of defined sequence
called cis-regulatory sequences, and thereby determine which of the thousands of genes in a
cell will be transcribed. Approximately 10% of the protein-coding genes in most organisms
produce transcription regulators, and they control many features of cells. Although each of
these transcription regulators has unique features, most bind to DNA as homodimers or
heterodimers and recognize DNA through one of a small number of structural motifs.
Transcription regulators typically work in groups and bind DNA cooperatively, a feature that
has several underlying mechanisms, some of which exploit the packaging of DNA in
nucleosomes.
Cell differentiation generally occurs without changes in the nucleotide sequence of a cell’s
genome.
1. Many processes are common to all cells, and any two cells in a single organism therefore
have many gene products in common. These include the structural proteins of
chromosomes, RNA and DNA polymerases, DNA repair enzymes, ribosomal proteins and
RNAs, the enzymes that catalyze the central reactions of metabolism, and many of the
proteins that form the cytoskeleton such as actin
2. Some RNAs and proteins are abundant in the specialized cells in which they function and
cannot be detected elsewhere, even by sensitive tests. Hemoglobin, for example, is
expressed specifically in red blood cells
3. When the patterns of RNA expression in different human cell lines are compared, the level of
expression of almost every gene is found to vary from one cell type to another.
Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to
Protein
A cell can control the proteins it makes by:
(1) controlling when and how often a given gene is transcribed (transcriptional control),
(2) controlling the splicing and processing of RNA transcripts (RNA processing control),
(3) selecting which completed mRNAs are exported from the nucleus to the cytosol and
determining where in the cytosol they are localized (RNA transport and localization control)
(4) selecting which mRNAs in the cytoplasm are translated by ribosomes (translational
control)
(5) selectively destabilizing certain mRNA molecules in the cytoplasm (mRNA degradation
control).
(6) selectively activating, inactivating, degrading, or localizing specific protein molecules after
they have been made (protein activity control). The regulation of protein activity, occurs
largely through covalent post-translational modifications including phosphorylation,
acetylation, and ubiquitylation.
, Summary:
The genome of a cell contains in its DNA sequence the information to make many thousands
of different protein and RNA molecules. A cell typically expresses only a fraction of its genes,
and the different types of cells in multicellular organisms arise because different sets of
genes are expressed. Moreover, cells can change the pattern of genes they express in
response to changes in their environment, such as signals from other cells. Although all of
the steps involved in expressing a gene can in principle be regulated, for most genes the
initiation of RNA transcription provides the most important point of control.
Transcription:
Transcription regulators recognize short stretches of double-helical DNA of defined sequence
called cis-regulatory sequences, and thereby determine which of the thousands of genes in a
cell will be transcribed. Approximately 10% of the protein-coding genes in most organisms
produce transcription regulators, and they control many features of cells. Although each of
these transcription regulators has unique features, most bind to DNA as homodimers or
heterodimers and recognize DNA through one of a small number of structural motifs.
Transcription regulators typically work in groups and bind DNA cooperatively, a feature that
has several underlying mechanisms, some of which exploit the packaging of DNA in
nucleosomes.
