Chromosome Structure: Questions Answered

[zmike]

I am in intro to genetics class and I am getting really confused with the terminology:

-Is a chromosome made up of 2 sister chromatids?
-are the 2 sister chromatids identiical?
-what's the difference between chromatins and chromatids? and between the kinetochore and centromere?

-gene structure: I saw a diagram showing this for a double helix DNA strand where gene X and gene y start and end at the same location on opposite strands

5' --------GENE X--------3'
3' --------GENE Y--------5'

If the 2 strands are complementary how can 2 genes be at the same location? since it's read 5' to 3' by the RNA transcriptase?

Thank you so very much!

 

[Ygggdrasil]

-Is a chromosome made up of 2 sister chromatids?

A chromosome, during mitosis, is made up of two sister chromatids. However, the term chromosome can also sometimes be used to refer to an individual chromatid (for example, during most of the cell cycle where our chromosomes are uncompacted).

-are the 2 sister chromatids identiical?

Yes (excluding any errors that occurred during replication).

-what's the difference between chromatins and chromatids? and between the kinetochore and centromere?

Is the general term used to describe the complex between genomic DNA and the proteins coating it (most notably the histone proteins). Chromatids refer to one of the linear DNA molecules that make up our genome.

The centromere is the sequence(s) of DNA that connect to microtubules and motor proteins during mitosis. The kinetochore is the term that refers to the complex of proteins and DNA that forms at the centromere during mitosis. The difference is subtle, but here is an example of how they are different. The centromere is always present on the chromosomes (even in the absence of the proteins that connect to it during mitosis), but the kinetochore forms only when the correct proteins assemble on the centromere during mitosis.

-gene structure: I saw a diagram showing this for a double helix DNA strand where gene X and gene y start and end at the same location on opposite strands

5' --------GENE X--------3'
3' --------GENE Y--------5'

If the 2 strands are complementary how can 2 genes be at the same location? since it's read 5' to 3' by the RNA transcriptase?

Most coding sequences in our DNA would have only one gene on one strand at that location. At the location of a gene, one DNA strand that acts as a template for the synthesis of mRNA and the non-template strand is not used for anything. However, some viruses, whose genomes must be much more compact than ours, do have overlapping genes where the non-template strand contains the information for a different protein.