1. Daughter cells that form as a result of asymmetric cell division may differ in a.size b.shape c.protein compositon d.all of the above
A.a
B.b
C.c
D.d
- · 有3位网友选择 A,占比37.5%
- · 有2位网友选择 B,占比25%
- · 有2位网友选择 D,占比25%
- · 有1位网友选择 C,占比12.5%
A.a
B.b
C.c
D.d
According to the text, the UK scientists have known that______.
A.women have more cells than men when they are born
B.women can replace the cells that enable the heart to beat
C.the female heart loses few of the cells with age
D.women never lose their pumping power with age
A.Although all cell types can divide,only stem cells differentiate after division.
B.Stem cells are able to divide to produce populations of cells that differentiate into a related set of cells.
C.Stem cells divide asymmetrically to give rise to one daughter cell that remains a stem cell, and a second daughter cell that differentiates into one or more cell types.
D.Stem cells have a special type of cell division in which they form small stems that then pinch off to give rise to the daughter cell.
A.5
B.10
C.20
D.40
A、Although all cell types can divide, only stem cells differentiate after division.
B、Stem cells are able to divide to produce populations of cells that differentiate into a related set of cells.
C、Stem cells divide asymmetrically to give rise to one daughter cell that remains a stem cell, and a second daughter cell that differentiates into one or more cell types.
D、Stem cells have a special type of cell division in which they form small stems that then pinch off to give rise to the daughter cell.
A.a
B.b
C.c
D.d
A.One of the simplest and most important is through a positive feedback loop, where a master transcription regulator activates transcription of its own gene,in addition to that of other cell-typespecific genes. Each time a cell divides, the regulator is distributed to both daughter cells, where it continues to stimulate the positive feedback loop.?The continued stimulation ensures that the regulator will continue to be produced in subsequent cell generations.?Positive feedback is crucial for establishing the “self-sustaining” circuits of gene expression that allow a cell to commit to a particular fate—and then to transmit that decision to its progeny.
B.Although positive feedback loops are probably the most prevalent way of ensuring that daughter cells remember what kind of cells they are meant to be,there are other ways of reinforcing cell identity. One involves the methylation of DNA.In vertebrate cells, DNA methylation occurs on certain cytosine bases. This covalent modification generally turns off the affected genes by attracting proteins that bind to methylated cytosines and block gene transcription. DNA methylation patterns are passed on to progeny cells by the action of an enzyme that copies the methylation pattern on the parent DNA strand to the daughter DNA strand as it is synthesizeD
C.Another mechanism for inheriting gene expression patterns involves the modification of histones. When a cell replicates its DNA,each daughter double helix receives half of its parent’s histone proteins, which contain the covalent modifications that were present on the parent chromosom
E.Enzymes responsible for these modifications may bind to the parental histones and confer the same modifications to the new histones nearby. It has been proposed that this cycle of modification helps reestablish. the pattern of chromatin structure found in the parent chromosome
D.Because all of these cell-memory mechanisms transmit patterns of gene expression from parent to daughter cell without altering the actual nucleotide sequence of the DNA,they are considered to be forms of epigenetic inheritanc
E.These mechanisms, which work together, play an important part in maintaining patterns of gene expression, allowing transient signals from the environment to be remembered by our cells—a fact that has important implications for understanding how cells operate and how they malfunction in diseas
E.
B.Although positive feedback loops are probably the most prevalent way of ensuring that daughter cells remember what kind of cells they are meant to be,there are other ways of reinforcing cell identity. One involves the methylation of DNA.In vertebrate cells, DNA methylation occurs on certain cytosine bases. This covalent modification generally turns off the affected genes by attracting proteins that bind to methylated cytosines and block gene transcription. DNA methylation patterns are passed on to progeny cells by the action of an enzyme that copies the methylation pattern on the parent DNA strand to the daughter DNA strand as it is synthesizeD
C.Another mechanism for inheriting gene expression patterns involves the modification of histones. When a cell replicates its DNA,each daughter double helix receives half of its parent’s histone proteins, which contain the covalent modifications that were present on the parent chromosom
E.Enzymes responsible for these modifications may bind to the parental histones and confer the same modifications to the new histones nearby. It has been proposed that this cycle of modification helps reestablish. the pattern of chromatin structure found in the parent chromosome
D.Because all of these cell-memory mechanisms transmit patterns of gene expression from parent to daughter cell without altering the actual nucleotide sequence of the DNA,they are considered to be forms of epigenetic inheritanc
E.These mechanisms, which work together, play an important part in maintaining patterns of gene expression, allowing transient signals from the environment to be remembered by our cells—a fact that has important implications for understanding how cells operate and how they malfunction in diseas
E.
A hematopoietic stem cell is defined as
A.a cell with extensive self-renewal and proliferative potential
B.a cell only to produce daughter cells with identical characteristics
C.a cell with the capacity to differentiate into the progenitors of all the blood cell lineages
D.a cell With the capacity to produce some hematopoietic growth factors such as SCF,GM-CSFs,et.a1.
E.a cell with the capacity to express some specific surface antigens such as CD34
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