basics of inheritance Flashcards
what is post-translational modification
the process of adding or removing parts of a sequence to a protein after translation
what is methylation of proteins
addition of a methyl group to histones
this affects how tightly DNA is wound controlling gene expression
it is reversible
what is glycosylation of proteins
addition of various sugars to the cell surface of proteins
it is reversible
what is ubiquination of proteins
addition of a 76 amino acid polypeptide that marks a protein for degradation
it is not reversible
what is phosphorylation of proteins
addition of a phosphate group by a kinase enzyme
regulates enzyme function by affecting the active site and substrate binding
it is reversible
what is protein targeting
a signal sequence within the protein that shows it where to go within the cell
what is the structure of amino acids
a carbon atom surrounded by a variable side chain known as an R group, an amino group (NH3)
and a carboxyl group (COOH)
the R groups can have different charges, polarities, shapes and sizes
what is the primary structure of a protein
the sequence of amino acid residues which is determined by the DNA sequence that encodes it
peptide bonds form between the N of the amino group and the C of the carboxyl group
rigid structure as there is no rotation around the peptide bond
what is the native form of a protein
the correctly formed structure of a protein caused by peptide bond formation
it is thermodynamically stable
what is the secondary structure of a protein
regular repeated structures stabalised by hydrogen bonds between polar side chains
it can either form an alpha helix or a beta pleated sheet
how does an alpha helix protein form
when the hydrogen bonds form between amino acids that are 4 residues apart to form a helix
how does a beta pleated sheet protein form
when the hydrogen bonds form between amino acids on different strands of the protein
the strands can run antiparallel or parallel to each other
what is the tertiary structure of a protein
tightly-packed, thermodynamically stable 3D structure determined by van der waals forces between side chains and sometimes disulfide bridges
how do hydrogen bonds form in a protein
side chains on an amino acid are electrically charged and polar so hydrogen bonds can form
how do van der waals forces form in a protein
weak, temporary interactions between polar side chains
what are disulfide bridges in a protein and why do they form
bonds that form between two cysteine side chains as they contain sulfur atoms that can form cross-links between parts of their primary sequence
they form in proteins that are exposed to harsh conditions to strengthen the tertiary structure
what is the quaternary structure of a protein
only some proteins have a quaternary structure and it forms when multiple polypeptides come together to form a larger structure with multiple subunits
what is segregation of genes (Mendel’s law)
genes come in pairs and individuals only pass one gene onto their offspring
what is independent assortment of genes (Mendel’s law)
different genes are passed on separately
what is dominance of genes (Mendel’s law)
in an individual with two alleles the gene will express the dominant form
what are the 4 things needed for evolution (Mendel’s law)
replication of genetic information
storage of genetic information
expression of genetic information
variation through mutations
what is the Sutton-Boveri theory of chromosomal inheritance
suggested that different combinations of chromosomes causes variation
chromosomes are required for embryonic development
chromosomes are linear structures that carry genes
what did Sutton and Boveri observe in their experiment
chromosomes group together in pairs and separate to reduce the chromosome number in gametes during meiosis
what was the experiment that led to the discovery of the transforming principle
there are 2 main strains of the bacteria strep: S (smooth) that contains a capsule and R (rough) that doesn’t have a capsule, only the S strain is virulent
1. the S strain was boiled breaking open the cell to form extract (no capsule)
2. the extract was injected into mice that survived showing it was the capsule causing virulence
3. the S extract was injected alongside the live R strain and the mice died
this shows that the DNA was transferred to the R strain encoding the enzyme that forms the capsule
what is Frederick Griffith’s transforming principle
that bacteria can transfer genetic material that changes the genotype of the cell
what is the structure of a DNA nucleotide
made up of a pentose sugar deoxyribose, a phosphate group and an organic base (adenine, guanine, cytosine or thymine)
what are purine and pyrimidine DNA bases
purine: 2 carbon rings in their structure e.g. adenine and guanine
pyrimidine: one carbon ring e.g. cytosine and thymine
how do phosphodiester bonds form
condensation reaction between the 5’ phosphate group and 3’ hydroxyl group
so DNA is built up in a 5’-3’ direction
what was the experiment carried out by Edwin Chargaff to show proportions of bases
used paper chromatography to separate and isolate bases from different species
what did Edwin Chargaff discover about the proportion of bases
all species have equal numbers of purine and pyrimidine bases
all species have equal numbers of A+T and C+G
different species have different proportions of bases e.g. some are AT-rich and some are GC-rich
why is base pairing important in DNA replication
so DNA polymerase knows which nucleotides to add
what are chromosomes
long, linear DNA molecules with genes bound to histones
contain a centromere for spindle fibres to attach to
how was X-ray crystallography used to find the structure of DNA
- a pure solution of DNA was obtained and crystallised
- concentrated X-ray beam was shone through it and the DNA molecules blocked the beam refracting it
this showed that DNA has an X shape with a regular, repeating structure
what did Watson and Crick discover about the structure of DNA
A+T and G+C bases are joined by hydrogen bonds and the strands run antiparallel
is has a double helix structure with major and minor grooves
why does the width of DNA stay constant
2 purines are always joined by a hydrogen bond to a pyrimidine
what are transcriptional regulators
proteins that bind to regulatory sequences at gene promoters on DNA
they stimulate or inhibit transcription by bending DNA
what are restriction endonucleases
enzymes that cut DNA at specific palindromic sequences
cut DNA at sequences 6-10 base pairs
used in bacteria to protect against viruses
what is process of semi-conservative replication
- DNA helicase breaks H bonds between base pairs separating strands and forming a replication bubble containing 2 replication forks
- single-strand binding protein enzyme binds to the template strands to stop them reannealing and another enzyme topoisomerase prevents overwinding by making small cuts in DNA to relieve pressure
- primerase adds primers to the 3’ end of the template and DNA polymerase adds nucleotides
what is the leading strand of DNA
DNA replicated towards the replication fork and continues without breaks
what is the lagging strand of DNA
DNA replicated away from the replication fork and is discontinuous as more primers are needed
smaller fragments called okazaki fragments are formed that are joined by DNA ligase
what are telomeres in DNA
repetitive, short non-coding sequences of DNA at the end of chromosomes that fill in the gap left by primers
they protect chromosomes to prevent loss of DNA
replenished by telomerase using an RNA template
what does the cell theory suggest
multicellular organisms are derived from a single cell
all cells are able to obtain energy and utilise available chemical compounds to grow
all cells use hereditary information that is stored in each cell and passed on
why are non-polar amino acid side chains found in the interior of globular proteins
they are hydrophobic so don’t interact with polar water molecules outside the protein
what are phage ghosts in bacteriophages
protein coats that surround bacteriophages
they protect nucleic acid from degradation, allow bacteriophages to attach to the host cell and inject its nucleic acid into the host for infection
how was bacteriophage genetic material observed
- bacteriophage was grown in a 32P and 35S medium to radioactively label the DNA and protein in the phage ghost separately
- the bacteriophage infected unlabelled bacteria and only the nucleic acid entered the host cells
- the infected host cells were blended to remove phage ghosts and centrifuged to produce a pellet containing bacteria and supernatant containing phage ghosts
- the pellet contained labelled DNA showing DNA is injected into the host cell for phage reproduction
