Lecture 2 Flashcards
What is the purpose of the nucleus?
Controlling center of the cell.
Contains linear DNA molecules
What is the function of nuclear envelope?
Double layered membrane complex.
Separates the nucleus from cytoplasm.
Separates ‘‘copy’’ of information (mRNA synthesis) from protein synthesis
Outer nuclear membrane consists of?
It’s linked with rough ER
Inner nuclear membrane consists of?
Contains specific set of integral membrane proteins that establish connections to chromatin and with nuclear lamina
What is the function of nuclear pore?
Protected exchange of components between the nucleus and cytoplasm
What can you tell about the linkers of nucleoskeleton and cytoskeleton (LINC complex?)
It positions the nucleus.
It coordinates nuclear and cytoplasmic activities.
Involved in mechanical force transmission from cytoskeleton to the nucleus
What is nuclear lamina?
Structure attached to the inner membrane and chromatin
What does nuclear lamina consists of?
Proteins called nuclear lamins.
A-type, B-type and C-type lamins
A and C are isoforms, coded by one gene
What is the function of nuclear lamina?
Lamina binds to the integral proteins of inner membrane.
What are laminopathies?
Changes in the sequence of lamins and lamina integrating proteins, that codes DNA regions -> leads to group of inherited disorders
What is nucleoplasm?
A jelly like fluid inside the nucleus, it’s major components are nucleoproteins
What are histones?
They are high MW proteins that contains basic amino acids, and have a positive charge.
How many classes of histones there are?
Total of five
H1, H2s, H2B, H3, H4
What is the main function of histone?
It contributes to the packing of DNA -> DNA is wrapped around histone octamer complex
How does the Histone-DNA-wrapping happens?
Postively charged amino acids of histones will form ionic bounds with negatively charged DNA
What are non-histone proteins?
Small, acidic proteins or enzymes (DNA or RNA polymeraze etc.)
Majority of the DNA is packed into? (in eukaryotic cell)
Nucleosomes (Histones+DNA)
What are nucleosomes made of?
Eight histone molecules (octamer)
H2A, H2B, H3, H4
Linker DNA?
DNA that links nucleosomes one to the next
With what linker DNA tightly bounds with?
Histone H1 ->This complex closes nucleosome and form chromatosome
What happens in Interphase?
Cell is actively expressing its genes and synthesizing proteins, DNA is replicated and chromosomes are duplicated.
Ones DNA replication is complete, what phase can be unlocked?
M phase.
What happens in M phase when mitosis occurs and the nucleus is divided into two daughter nuclei?
The chromosomes condense, the nuclear envelope breaks down and the mitotic spindle forms
What happens when mitotic chromosomes are captured by the mitotic spindle?
One complete set of chromosomes is pulled to each end of the cell, nuclear envelope re-forms around each chromosome set
What happens in the final M phase?
The cell divides to produce two daughter cells
What can you tell about euchromatins?
They have a high level of gene expression and they are early replicative, less condence
What can you tell about heterochromatins first of all?
Limited / no gene expression, associated with telomere and centromere.
Late replicative.
Only in eukaryotic cells.
What is a constitutive heterochromatin?
Contains highly repetitive sequences of genetically inactive DNA.
Serves as structural element of the chromosome
It is stable during all stages of development in all tissues.
What is a facultative heterochromatin?
It makes up the inactive X chromosome in female somatic cells (Barr body).
It is characterized by presence of LINE-type repeated sequences.
It’s reversible.
What are constitutive- and facultative heterochromatin methylated on?
Constitutive is mythylated on cytosine.
Facultative is methylated on CpG islands (gene control regions).
Functions of heterochromatin?
Centromere function.
Organisation of nuclear domains.
Gene repression.
What is a chromosome?
The tight coiling of the 250 nm fibre produces the chromatid of chromosome.
What happens to chromosome in the S phase? (interphase)
Replication of DNA takes place and two identical chromatids are produced.
What phase chromosomes can be observed during cell devision?
Metaphase chromosomes
What can you say about metaphase chromosomes?
Cohesin attaches to the chromosome during replication and ensures sister chromatic contact during cell division.
Sister chromatids?
Two copies of one chromosome.
What are telomeres?
Repeated nucleotide sequences which are species specific.
TTAGGG repeats in humans.
3’ strand ended is single stranded, forms a cap.
Telomeres functions?
Counts how many times cell can divide; maintaining normal genome.
Uncapped telomeres are able to?
Activate the DNA damage response and cause end-to-end fusions, resulting in chromosomal instability
Karyotype: somatic cells have how many chromosomes?
Diploid set of chromosomes (2n) - 46
Karyotype: germ cells have how many chromosomes?
Haploid set of chromosomes (1n) - 23
Sex-chromosome?
Determines the sex and sex-linked features.
Humans have two sex chromosomes: X and Y
Each individual cell contains two sex chromosomes which are?
In diploid cell Female-XX and Male -XY
Difference between the activation of X chromosome in male and female?
In females, one X chromosome is inactivated (Barr body) in all somatic cells.
In males, X chromosome is active (no barr body)
How many barr bodies in female: 47, XXX?
Two, because female needs one active, would not lead to any specific diseases.
What is the function of a nucleolus?
The site of a ribosomal (rRNA) transcription, ribosomal assembly
What can you say about prokaryotic chromosome?
Nucleoid consists of DNA and RNA molecules with nucleoproteins, membrane free.
DNA is circular, not attached with histones.
One information of genetic copy - haploid organism.
What can you say about prokaryotic chromosomes plasmids?
Contains small part of genetic information which contributes to the sensitivity to various toxic substances (antibiotics etc.)
Plays a role in genetic recombination
Mitochondrial chromosome?
Self-replicating organelle.
It’s matrix has a complex mixture of proteins and enzymes.
Important for synthesis of ATP molecules, mitochondrial ribosomes, tRNA’s and mitochondrial DNA
What is mitochondrial DNA? (mtDNA)
Circular, negatively supercoiled.
Contains 4-5 mtDNA copies.
Toposiomerases: Top1mt, Top3alpha, Top2beta
Features and functions of the mitochondria?
Self-replication.
Aerobic ATP production.
Ion homeostasis.
