STRUCTURE AND FUNCTION OF CELL / NUCLEUS / CHROMATIN Flashcards
WHERE DOES TRANSCRIPTION TAKE PLACE IN EUKARYOTES?
nucleus
WHERE DOES TRANSLATION TAKE PLACE IN EUKARYOTES?
cytoplasm
WHERE DOES DNA REPLICATION TAKE PLACE IN EUKARYOTES?
nucleus
WHAT IS THE NUCLEAR ENVELOPE AND ITS FUNCTION?
separates the nucleus from the cytoplasm
-2 layers + perinuclear space (both membranes contain their own distinct complement proteins and outer membrane is connected to fibers of cytoskeleton by fibrous proteins (nesprins)
-nuclear pores which are protein forming channels that regulate the transport of substances from the cytoplasm to the nucleus
WHAT IS THE NUCLEAR LAMINA AND WHAT ARE ITS FUNCTIONS?
network of lamins underneath the nuclear envelope
-provides mechanical support for nuclear envelope
-disintegration and reintegration of nuclear envelope during mitosis
1: phosphorylation – lamins disintegrate and carry bits of nuclear envelope with them
2: dephosphorization – lamins begin to reintegrate and reform the nuclear envelope
WHAT KINDS OF CHROMATIN ARE FORMED BY CHROMOSOMES IN EUKARYOTIC CELLS?
linear chromosomes
WHAT IS THE BARR BODY?
– one of two X chromosomes in female is inactive (due to heterochromatin) and is condensed and during interphase is visible under a microscope as a dark dot sticking to the side of the nucleus.
BY HOW MUCH DOES DNA SHORTEN WHEN CONDENSED?
to 1/10 000 of its original length
WHAT IS THE NUCLEOLUS AND ITS FUNCTION?
contains rRNA for the production of ribosomes
-not membrane bound
WHEN DOES THE SYNTHESIS OF HISTONES TAKE PLACE?
during replication of DNA (S phase of cell cycle)
WHAT IS THE FUNCTION OF NON HISTONE CHROMOSOMAL PROTEINS?
determine the spatial arrangement of chromosomes (they have solenoids anchored
to them)
WHAT HISTONES ARE CONTAINED IN EUKARYOTIC CHROMOSOMES?
H1
H2A
H2B
H3
H4
WHAT IS THE FUNCTION OF HISTONES?
they coil DNA → they build nucleosomes
WHAT ARE THE DIFFERENCES BETWEEN PROKARYOTIC AND EUKARYOTIC CHROMOSOMES?
- euk. chromosome = linear
prok. chromosome = circular
-euk. chromosome has more base pairs (10^8) instead of (10^6)
WHAT IS THE STRUCTURE OF THE NUCLEOSOME?
-octamer of histones (2x H2A, 2x H2B, 2x H3, 2x H4)
-146/147 base pairs wrap around octamer
-around 60 bae pairs of free DNA in between nucleosomes
-H1 histone connects nucleosomes (condensation of chromosomes)
-1 nucleosomes is around 200 base pairs
EXPLAIN THE STRUCTURAL LEVELS OF EUKARYOTIC CHROMOSOME.
- Double helix of DNA – diameter of strand is 2 nm
- Individual molecule of DNA is negatively charged à histones neutralize it and allow for the condensation of DNA - double helix wraps around the 8 histones – formation of nucleosome with the dimeter of the strand being 11 nm
- H1 histone causes further condensation into a solenoid -> chromatin strand with the dimeter of 30 nm
- solenoid is anchored onto the strand by non-histone proteins and cannot undergo further condensation -> loops of
chromatin - 300 nm - further condensation forms chromosome -> condensed part of chromosome = chromatid - 700 nm
- whole mitotich chromosme - 1400 nm = 1,4 x 10-3 m
EXPLAIN THE STRUCTURE OF THE MITOTIC CHROMOSOME.
-2 chromatids
-centromere = central part, site of connection between chromatid and mitotic spindle
-telomere = ends of chromosome, protects against degradation of DNA/ random pairing of chromosomes
WHAT IS THE REGULATION OF THE CHROMATIN STRUCTURE.
chromatin remodelling complexes – manipulate the level of condensation of DNA in nucleosomes – by modifying histones
A: acetylation - acetyl loosens chromatin; acetylate histones mainly found in euchromatin
B: methylation – methyl tightens chromatin; methylated histones mainly found in heterochromatin
C: phosphorylation – can loosen or tighten chromatin structure; depends on what is phosphorylated
- histones code = determines which genes are expressed or not
WHAT ARE THE POST-TRANSCRIPTIONAL MODIFICATIONS?
-known as the histone code
-determine which genes are shown and not
METHYLATION = methyl tightens chromatin → methylated histones mainly found in heterochromatin
PHOSPHORYLATION = can loosen or tighten chromatin → depends on what is phosphorylated
HOW MANY CHROMATIDS ARE IN THE HUMAN BODY?
92, double the number of chromosomes (46)
WHAT IS THE DIFFERENCE BETWEEN TOPOISOMERASE I AND TOPOISOMERASE II?
topoisomerase I is ATP dependent while topoisomerase II is not ATP dependent
WHAT IS A MONOCISTRONIC GENE?
transcript encodes for a single protein
WHAT IS A POLYCISTRONIC GENE?
transcript encode for 2 or more proteins
EXPLAIN HISTONE POSTTRANSLATONAL MODIFICATIONS
modifications via: methylation, acetylation, phosphorylation, ubiquitination
LYSINE ACETYLATION (HAT) -> abolishes positive charge = less compact nucleosome & transcription activated
LYSINE METHYLATION -> does not influence positive charge - serves as a mark - transcription can be activated or inactivated
LYSINE DEACTEYLATION (HDAC)
WHAT DOES METHYLATION OF CYTOSINE IN CG DINUCLEOTIDES CAUSE?
-> interferes with binding of TFs
-> becomes marked and recognized by methyl binding proteins
