Biophysics Flashcards
What are the names of the 3 types of cells that were made from a common ancestor several billion years ago (called domains)?
Bacteria, archaea and eukarya
Which two types of domain are very similar?
Bacteria and archaea
What determines the divisions of the domains/cell types?
The similarities and differences in ribosomal RNA sequences
What are the two types of cells?
Eukaryotic and prokaryotic
What is the main difference between eukaryotic and prokaryotic cells?
Eukaryotic cells have a nucleus that contain genetic material (DNA) and prokaryotic cells do not have a nucleus
Where are eukaryotic cells found?
In animals, plants, fungi, protozoa and algae
Are bacteria eukaryotic or prokaryotic?
Prokaryotic
Are eukaryotic organisms uni- or multi- cellular or either?
Either
Are prokaryotic organisms uni- or multi- cellular or either?
Always uni-cellular
What can cells do?
Regulate biochemical processes, control chemical flux between compartments, have structural integrity, exert forces and react dynamically
What are organelles and are they membrane bound?
They are compartments within a cell that have specific specialised functions and they can be membrane bound (made of lipids) or membraneless
Can organelle compartments have completely different protein and ion composition to compartments surrounding it?
Yes
What can the structural features of the interior of a eukaryotic cell be built from?
Lipids or proteins
What is the outside ‘fabric’ of the cell called and what is it made of?
Plasma membrane and its made of lipids
Name some organelles in eukaryotic cells
Nuclear membrane, the Golgi Apparatus, the Endoplasmic Reticulum and the Mitochondria
What are microtubules and actin filaments and what are they made of?
Structural features in eukaryotic cells (eg cell shape) and are made of proteins
What part of the cell contains the genome?
The nucleus
Does knowing the genome tell you anything about what an individual cells does or is doing?
No
What surrounds the nucleus and why does it contain pores?
The nuclear envelope/membrane and the pores allow messenger RNA diffusion in and out
What is the central dogma of cell biology?
The theory that genetic information flows only in one direction, from DNA, to RNA, to protein
How do cells regulate their function?
Controlling the concentration of various proteins
Do all the cells in the body contain the same DNA?
Yes
What is a phenotype and genotype?
The genotype is a set of genes in DNA responsible for unique trait or characteristics while the phenotype is the physical appearance or characteristic of an organism resulting from their genetic makeup
What causes the differences between types of cell?
The regulation of protein expression and degradation
What is a gene?
A short section of DNA that carries the information to make a molecule (usually a protein) and can vary in size
What is the genome?
The entire sequence of genes and bases
What is a chromosome and how many are there in a cell?
It is a tightly packed coiled of DNA and there are 23 pairs so 46 overall
What is a protein?
A large molecule made up of chains of amino acids, which are essential to the functioning of our cells
What are alleles in humans?
They are different forms of the same gene, one from our biological mother, one from our biological father so there is one on each chromosome
What are the main two classes of nucleic acids?
DNA and RNA
What is a nucleotide?
The basic building block of nucleic acids and consists of a sugar molecule (either ribose for RNA or deoxyribose for DNA) attached to a phosphate and a base
Why are DNA and RNA called nucleic acids?
They are acids and found in high concentration in the nucleus of the cells
Although DNA and RNA are very similar, what makes them different?
RNA is less stable and in shorter chains
What are the bases called?
Adenine (A), cytosine (C), guanine (G), thymine (T) (DNA only) and uracil (U) (RNA only)
What are the base pairs in DNA and RNA?
G with C for both, A with T for DNA and A with U for RNA
How long is a base pair roughly?
3.4 times 10 to the -10 metres
What does DNA look like?
Two strands intertwined into a helix, with the sugar-phosphate on the outside and the bases on the interior of the strand
RNA and DNA contain ribose sugars, how are the carbon atoms in the sugars numbered?
1’ to 5’
Why aren’t the carbon atoms shown on the diagrams for deoxyribose and ribose?
For clarity, but they are in fact on the corners
What is the difference between the ribose and deoxyribose sugars?
Ribose has a hydroxyl group (OH) on the 2’ carbon atom, whilst deoxyribose only has hydrogen on the 2’ carbon atom
Is ribose the same thing as d-ribose?
Yes
Where are the bases attached to each sugar?
At the 1’ carbon atom position
How are sugars linked in DNA and RNA to make the backbone of a strand?
Phosphodiester bridges
What is the phosphodiester bond?
It links the 3’ carbon atom of one sugar molecule to the 5’ carbon atom of another, which forms a repeating sugar-phosphate backbone
What element do all the bases include?
Nitrogen
What two bases are derivative of purine and which three bases are derivatives of pyrimidine?
A and G are derivatives of purine, whilst C, T and U are derivatives of pyrimidine
What is a codon?
A DNA or RNA sequence of 3 nucleotides which together form a unit of genetic code
What does it mean that the base sequences of nucleic acids are always written in the 5’ to 3’ direction?
Any single strand will have an unbound 5’ phosphate at one end and nucleotides are added only to the 3’ end of the growing strand. It is always read in the 5’ to 3’ direction
What direction are DNA and RNA synthesised in living cells?
5’ to 3’ direction
What is electronegativity?
It is the measure of the tendency of an atom to attract a bonding pair of electrons
What happens if an atom is more electronegative than another?
It will attract the electron pair more than the other atom, which means it has more than its fair share of electron density and becomes negative and the other atom positive, creating a dipole
What are hydrogen bonds?
A hydrogen atom covalently bonded to a very electronegative atom and another very electronegative atom with an available lone pair of electrons
How are the complementary base pairs on separate strands connected to one another?
Hydrogen bonds
Who and when was the double helix postulated?
Crick and Watson in 1953
What is Chargaff’s rule?
For any organism, the concentration of bases obey that A/T and C/G is approximately 1 but T/G varies widely
What does it mean that the two strands of DNA have complementary base sequences?
They carry the same information in different forms
If the strands in a double helix are separated, how can the original double helix be built from each one individually?
Templated polymerisation
What are the main differences between the DNA types?
The number of base pairs per turn of the helix, the tilt of the base pairs, the diameter of the helix and the nature of the grooves of the helix
What form of DNA is seen in nature?
B form
How many residues per turn of the axis does B form DNA have and how are they angled?
10 and they are virtually planar and perpendicular to the helix axis
What is the diameter of B form DNA and what is the nature of the grooves on it?
Around 2.2nm and the major groove is wider than the minor groove that are on opposite sides of the helix
Is A, B and Z form DNA right or left handed helices?
A and B are right, Z is left
What is the differences between A and B form DNA?
B form is wider and stubbier, with 11 residues per turn of the helix and a few angstroms wider in diameter. The bases make an angle of 20 degrees with the helix axis in B form but are also planar
What is the difference between Z form DNA and the other two types?
The major and minor grooves of the Z form DNA show little difference in width
What is chromatin?
The formed DNA double helix in the cell nucleus that is packaged by special proteins called histones is chromatin and is the material that chromosomes are made from
What is a nucleosome?
A nucleosome is the basic structural unit of DNA packaging in eukaryotes. It is a segment of DNA wound around eight histone proteins and resembles thread wrapped around a spool. The nucleosome is the fundamental subunit of chromatin