Eukaryotic Chromosomes Flashcards
Telomere
a compound s-re at the end of a linear chromosome, which contain specific repetitive sequences (base pairs for example like GGU, GGU, GGU, GGU).
Kinetochore are?
It’s the protein unit (mixture of DNA and proteins), which are found in the centromere (black dots - kinetochores) to which spindle fibers attach to in the chromosome.
Nucleosome (1-st level of packaging)
beadlike structure consisting of double stranded DNA wrapped around histone proteins, which make up the nucleosome. Each “bead” of the nucleosome contains 5 different histone proteins.
Satellite DNA
highly repetitive (tandem) non-coding DNA found near the centromere (heterochromatic centromeric regions - condensed) in higher eukaryotes.
Chromatin
mixture of DNA, protein (such as histones), and RNA in the eukaryotic nucleus, which make up the chromosome
Cohesin is?
a protein complex that binds sister chromatids to each other throughout metaphase (until anaphase), which can be found at both the centromere and along the chromosome arms.
Histones
small basic (positively-charged) proteins, which can bind to the phosphates (negatively charged) along the DNA backbone.
During what stage of the cell cycle is it most crucial to synthesize new histone proteins?
cell requires increase in histone production (G1 phase) prior to S phase on the cell cycle.
S phase creates the new DNA strand, which binds to the newly made histone proteins
The human genome contains 60 histone genes, with 10-15 genes of each type (H1, H2A, H2B, H3, and H4). Why do you think the genome contains multiple copies of each histone gene
More templates that the cells can transcribe simultaneously, allowing the more rapid production of histone proteins. This means that the more RNA polymerase transcribes (reads) templates, the more and faster we get protein (such as histone)
What DNA sequences are commonly found at human centromeric regions?
Satellite DNA
Chromatid
a half of each chromosome
What telomeres contain at the ends of chromosomes?
They contain specific repetitive (tandem) sequences (base pairs, for example like GGU, GGU, GGU, GGU)
How telomeres protect the ends of chromosomes?
Telomeres protect the ends of the chromosome from being digested (broken down) by preventing the loss of base pairs during replication
What is the function of telomerase enzyme?
Telomerase enzyme (purple circle) + RNA (reg segment) rebuilds telomeres (light blue and dark blue) because a little bit is lost each replication cycle (so it stays the same).
Ribonucleoprotein consists of
Telomerase (enzyme) + RNA= Ribonucleoprotein
What advantage the telomerase activity provide the diseased tumor cells?
This means that tumor cells will stay always alive because of high level of telomerase activity.
Segregation definition
the separation of pairs of alleles at meiosis (so they go to different gametes - sex cells).
Centromeres definition
It’s the structure on the chromosome that holds 2 sister chromatids together by cohesion proteins and serves as the point of attachment of the kinetochore proteins (to which spindle fibers attach)
A tandem repeat is
A tandem repeat is a sequence of two or more DNA nucleotides that is repeated in such a way that the repeats lie adjacent to each other on the chromosome. The tandem repeat can be coding and noncoding.
Noncoding or Coding tandem repeats (Most prominent)?
a pattern of 2 or more nucleotides is repeated on the noncoding (or coding) DNA strand, lie directly adjacent to each other (side by side)
Ex. A-T-T-C-G-A-T-T-C-G-A-T-T-C-G (5 base pairs repeat,
where bases are the part of the nucleotide)
How much do we have histone proteins and what are they?
Nucleosome contains 5 different histone proteins, they are: core histones (H3, H4, H2B and H2A) and the linker histone (H1).
What is the octamer?
An octamer of histone proteins is composed of two copies, 4 different types of core histone proteins, which totally gives 8 core histones. They are 2 the same core histones. For example: H2A and H2A, H2B and H2B, H3 and H3, H4 and H4 (total 8).
What is the Nuclear Matrix?
Nuclear Matrix is the filamentous network of fibers/proteins
(purple around white circle - nucleoplasm) found throughout the inside of the nucleus.
Euchromatin vs. Heterochromatin
a. Euchromatin: less condensed regions = transcriptionally active
b. Heterochromatin: more condensed regions= transcriptionally inactive (because RNA polymerase can’t read them)
What are the types of heterochromatin?
(1) Constitutive heterochromatin
- Usually contain highly repetitive sequences (repeating base pairs)
(2) Facultative heterochromatin
This means that heterochromatin can become euchromatin, and vice versa.
What happens if the chromosomes don’t have the telomere?
Without telomeres chromosomes stick together.
When 2 chromosomes that lost telomeres stick together, they can’t separate, and anaphase helps them in separation only with telomeres.
Alphoid family meaning?
are tandem repetitive (specific) base pair sequences, which are mainly found in the centromere regions and critical to centromere function.
In humans, most recognized satellite DNA sequences are part of alphoid
Normal cells vs Tumor cells telomerase activity
Normal somatic cells have little/no telomerase —> aging of the cells
Embryonic cells have active telomerase, which help the telomere to regrow
Tumor cells exhibit high levels of telomerase activity, which leads to growth of telomere.
What are the structural genes?
- Genes located between the centromeric and telomeric regions along the entire chromosome (from the beginning after telomere till the middle)
A single chromosome usually has a few hundred to several thousand genes
What is the yellow “tail” of nucleosome?
positively charged amino end of histone proteins
What is the second level of packaging of nucleosomes?
Nucleosome associate (connect) with each other through DNA to form a more compact (tight) structure (thin s-re) - 30nm fiber (second level of packaging)
Histone H1 protein function
Histone H1 plays a role in the compaction of DNA (shortening)
What is the final packings of nucleosome?
Final packings of nucleosome occurs when the fiber is organized (differently)
into loops, scaffolds, and domains.
Origins of Replication (OARs) function?
- help DNA replication to occur
DNA replication is the process by which DNA makes a copy of itself during cell division. - contain many DNA of eukaryotes approximately 100,000 bp apart
There are many Origins of Replication (OARs) in eukaryotic DNA,
which are approximately 100,000 bp apart.
