cell biology (biochem) Flashcards
nucleus
- what does it contain?
- double membrane (only organelle with double membrane)
- chromosomes
- nucleolus
what happens in nucleolus?
most of RNA synthesis
what is plasma membrane made of?
phospholipid bilayer
cholesterol - to be more rigid
protein transporters (allow water soluble molecules to pass)
receptors (site of cell signalling)
smooth endoplastic reticulum
1. function
2. which cells is it especially abundant in
- site of phospholipid and fatty acid synthesis
- liver cells (modifies/ detoxifies toxins and carcinogens)
rough endoplastic reticulum
1. what’s bound to them and its role
2. which cells especially abundant in
3. how do cells leave and where do they go?
- ribosomes - sythesise all the proteins (site of translation)
- ones that produce lots of protein
- plasma cells (produce Abs)
- pancreatic acinar cells (produce digestive enzymes) - membrane bound vesicles to Golgi apperatus
mitochondria
1. what happens there?
2 .structure
3. how is its DNA inheritted
- respiration - ATP production
- smooth outer membrane
convulated inner membrane (indentations called cristae)
gap between 2 membranes = intermembrane gap
mitochondrial matrix = space inside inner membrane - maternal
peroxisomes and lysosomes
- what is their role?
disposal system
lysosome
- pH
- 2 mechanisms by which materials are brought in
- pH 4.8
- endocytosis, phagocytosis
peroxisomes
- role
- which substances do they mainly act on
- oxidise synthetic substances (contain oxidase enzymes)
- mainly oxidise fatty acids
- toxic molecules in blood are cleared by peroxisomes (especially in liver and kidneys)
cytosol
- what does it contain
organelles and cytoskeleton
role of cytoskeleton
gives cell rigidity and strength
so allows it to migrate
3 classes of fibre making up cytoskeleton
- microfilaments
- intermediate filaments
- micortubules
4 major classes of cell adhesion molecules
- cadherins
- immunoglobulins
- selectins
- integrins
cadherins
- how do they cause adhesion
- main role
- homophilic (to self), calcium dependent
- transmembrane linker proteins
immunoglobulin-like molecules
- how do they cause adhesion
- example
- hetero and homo-philic
- NMACs (neural cell adhesion molecules)
integrins
- heterodynamic
- alpha and beta subunits
- communication between cytoskeleton and extracellular matrix
- binding of of WBC to endothelium
- extravsation or diepedesis
- defects can cause abnormal inflammatory responses
- bind more tightly
selectins
- where expressed
- role
- leucocytes, endothelial cells
- host-defence mechanism involving leucocytes and endothelial cells
- selectin mediated interactions result from weak bonds between neutrophil and endothelial cells
4 classes of cell junctions
- tight junctions
- adherens junctions & desmosomes
- hemidesmosomes
^^ above are adhering junctions - gap junctions
^^ are communicating junctions
what are gap junctions formed from?
from mirror images of protein units (con-exons) located in the plasma membranes of 2 cells
cytoplasms are connected by narrow water-filled channels
how do gap junctions work?
allow small signalling molecules to pass e.g. Ca2+ and cAMP but not large ones such as proteins
stages of mitosis
- prophase
- metaphase
- anaphase
- telophase
during prophase:
chromosomes condense
during metaphase:
sister chromatids produced during S phase become alligned in centre of cell
during anaphase:
sister chromatids separate and move to opposite ends of mitotic apperatus/ spindle
during telophase:
nuclear envelope breaks down
and reforms around the segregated chromosomes.
The final physical division of the cytoplasm to yield
two daughter cells is called cytokinesis
between which stages is:
- gap 1 (G1)
-gap 2 (G2)
why are there gaps?
G1= between M and S
G2= between S and M
(S= the synthesis phase)
gaps allow time for cell growth
what type of cells exist in G0 (quiescent state)?
non-dividing cells
when are the DNA damage checkpoints?
before and during S phase
what happens if DNA damage is detected during checkpoint?
the activity of a protein called cyclin-dependent
kinase 2 (CDK2) is inhibited and progression
through the cell cycle is stopped.
If the damage to theDNA is not repairable (for example using the DNA repair proteins BRCA1 and BRCA2), the cell undergoes apoptosis.
3 key proteins in regulation of cell cycle and how they work
APC
- activates Myc (a transcription factor) which induces the movement from G1 to S phase
p53
- detects DNA damage and inhibits cell cycle by blocking CDK2. also has role in apoptosis
ATM
- detects DNA damage and stops cell cycle (with p53)
- maintains normal telomere length i.e. counteracts chromosomal shortening with each round of replication
which layer are carcinomas derrived from?
endoderm or ectoderm
which layer are sarcomas derrived from?
mesoderm
leukaemias are class of sarcomas that grow from indivdual cells in blood
mutated oncogene alleles inheritance
dominant
tumour repressors/ loss of function mutations inheritance
recessive
APC mutation
- which cancer?
- what proto-oncogene mutates?
- what is the result of this?
- what else mutates?
- colorectal
- Ras (protein involved in signal transduction)
- loss of function of DCC (a tumour suppressor protein, defective in sister chromatid cohesion), loss of function of p53
- MMR (mismatch repair proteins)
oncogenic viruses examples (2)
Harvey sarcoma virus
- Ha-ras gene
- bladder tumours
Rous sarcoma virus
- (v-Src) protein, a mutation of (c-Src) protein a protein tyrosine kinase involved in signal transduction
are made of RNA
what do tumours need to keep growing?
how do they get this?
i) blood supply
ii) angiogenesis
ekeasing growth factors such as VEGF
examples of growth factors released in angiogenesis?
VEGF
basic fibroblast growth factor
transforming growth factor alpha
DNA structure
- base pairs
- a 5 carbon sugar (pentose) - ribose in RNA, deoxyribose in DNA
- phosphate back bone
what are the 4 base pairs?
adenine - thymine (urcacil in RNA)
guanine- cytosine
left ones = purines (fused by a pair of nitrogen containing ringe)
right ones= pyrimadines (fused by single nitrogen containing ring)
what does helicase do?
where does it sit?
unwind double helix and disrupts hydrogen bonds
replication fork
what does topiosomerase do?
breaks, untwists and reconnects chain further ahead of replication fork to prevent “tangles”
in DNA replication
what does DNA polymerase do?
adds on complimentary strands in DNA replication
in which direction does DNA polymerase work
i) in leading strand
ii) in lagging strand
i) 3 to 5
ii) 5 to 3
What are Okazaki fragments?
Discontinuous DNA fragments used to form new DNA in lagging strand
What does ligase do?
joins together DNA strands
explain RNA synthesis (transcription)
- DNA must denature (unwind)
- RNA polymerase binds to promoter region
- transcription occurs in 5 to 3 direction i.e. mRNA is made in 5 to 3 direction, polymerase moves in 3 to 5
what are the 2 DNA stands involved in RNA synthesis?
template strand = strand copied to make new strand
coding strand = strand not used
what is gene splicing?
what is alternative splicing?
- the removal of introns from RNA strand
- allows single gene to be translated into multiple similar proteins
what are:
- introns
- extrons
introns - non-coding sequences
extrons - coding sequences
what bond holds together amino acids?
peptide bond
what is a codon?
- a triplet of nucleotides in mRNA
- each codon codes for 1 amino acid (code is degenerate i.e. several different codon combos make 1 amino acid but same codon doesn’t make >1 amino acid
what is translation?
where does it happen?
mRNA –> protein
(also needs tRNA and rRNA)
ribosome
what is:
- primary structure of protein
- secondary structure
- tertiary structure
- quarternry structure
1 - sequence of amino acids in polypeptide chain
2 - folding of polypeptide chain (apha helix or beta chain)
3 - tertiary structure refers to
the folding of the polypeptide chain into an overall arrangement and this is achieved through hydrophobic interactions and disulphide bonds
4- the arrangement of multiple polypeptide chains (subunits) in multimeric proteins.
what is Southern blotting used for?
detecting presence and amount of a particular sequencr of DNA
what is northern blotting used for?
to detect the presence and amount of particular RNA sequences
what is Western blotting used for?
what technique does it use?
to detect the presence and amount of a specific protein in a tissue sample
gel electrophoresis
what is PCR used for?
to amplify a specific DNA or RNA sequence
what are DNA microarrays used for?
simultaneous analysis of expression of 1000s of genes
