basics of inheritance

Question 1

what is post-translational modification

Answer 1

the process of adding or removing parts of a sequence to a protein after translation

Question 2

what is methylation of proteins

Answer 2

addition of a methyl group to histones
this affects how tightly DNA is wound controlling gene expression
it is reversible

Question 3

what is glycosylation of proteins

Answer 3

addition of various sugars to the cell surface of proteins
it is reversible

Question 4

what is ubiquination of proteins

Answer 4

addition of a 76 amino acid polypeptide that marks a protein for degradation
it is not reversible

Question 5

what is phosphorylation of proteins

Answer 5

addition of a phosphate group by a kinase enzyme
regulates enzyme function by affecting the active site and substrate binding
it is reversible

Question 6

what is protein targeting

Answer 6

a signal sequence within the protein that shows it where to go within the cell

Question 7

what is the structure of amino acids

Answer 7

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

Question 8

what is the primary structure of a protein

Answer 8

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

Question 9

what is the native form of a protein

Answer 9

the correctly formed structure of a protein caused by peptide bond formation
it is thermodynamically stable

Question 10

what is the secondary structure of a protein

Answer 10

regular repeated structures stabalised by hydrogen bonds between polar side chains
it can either form an alpha helix or a beta pleated sheet

Question 11

how does an alpha helix protein form

Answer 11

when the hydrogen bonds form between amino acids that are 4 residues apart to form a helix

Question 12

how does a beta pleated sheet protein form

Answer 12

when the hydrogen bonds form between amino acids on different strands of the protein
the strands can run antiparallel or parallel to each other

Question 13

what is the tertiary structure of a protein

Answer 13

tightly-packed, thermodynamically stable 3D structure determined by van der waals forces between side chains and sometimes disulfide bridges

Question 14

how do hydrogen bonds form in a protein

Answer 14

side chains on an amino acid are electrically charged and polar so hydrogen bonds can form

Question 15

how do van der waals forces form in a protein

Answer 15

weak, temporary interactions between polar side chains

Question 16

what are disulfide bridges in a protein and why do they form

Answer 16

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

Question 17

what is the quaternary structure of a protein

Answer 17

only some proteins have a quaternary structure and it forms when multiple polypeptides come together to form a larger structure with multiple subunits

Question 18

what is segregation of genes (Mendel’s law)

Answer 18

genes come in pairs and individuals only pass one gene onto their offspring

Question 19

what is independent assortment of genes (Mendel’s law)

Answer 19

different genes are passed on separately

Question 20

what is dominance of genes (Mendel’s law)

Answer 20

in an individual with two alleles the gene will express the dominant form

Question 21

what are the 4 things needed for evolution (Mendel’s law)

Answer 21

replication of genetic information
storage of genetic information
expression of genetic information
variation through mutations

Question 22

what is the Sutton-Boveri theory of chromosomal inheritance

Answer 22

suggested that different combinations of chromosomes causes variation
chromosomes are required for embryonic development
chromosomes are linear structures that carry genes

Question 23

what did Sutton and Boveri observe in their experiment

Answer 23

chromosomes group together in pairs and separate to reduce the chromosome number in gametes during meiosis

Question 24

what was the experiment that led to the discovery of the transforming principle

Answer 24

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

Question 25

what is Frederick Griffith's transforming principle

Answer 25

that bacteria can transfer genetic material that changes the genotype of the cell

Question 26

what is the structure of a DNA nucleotide

Answer 26

made up of a pentose sugar deoxyribose, a phosphate group and an organic base (adenine, guanine, cytosine or thymine)

Question 27

what are purine and pyrimidine DNA bases

Answer 27

purine: 2 carbon rings in their structure e.g. adenine and guanine pyrimidine: one carbon ring e.g. cytosine and thymine

Question 28

how do phosphodiester bonds form

Answer 28

condensation reaction between the 5' phosphate group and 3' hydroxyl group so DNA is built up in a 5'-3' direction

Question 29

what was the experiment carried out by Edwin Chargaff to show proportions of bases

Answer 29

used paper chromatography to separate and isolate bases from different species

Question 30

what did Edwin Chargaff discover about the proportion of bases

Answer 30

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

Question 31

why is base pairing important in DNA replication

Answer 31

so DNA polymerase knows which nucleotides to add

Question 32

what are chromosomes

Answer 32

long, linear DNA molecules with genes bound to histones contain a centromere for spindle fibres to attach to

Question 33

how was X-ray crystallography used to find the structure of DNA

Answer 33

1. a pure solution of DNA was obtained and crystallised 3. 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

Question 34

what did Watson and Crick discover about the structure of DNA

Answer 34

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

Question 35

why does the width of DNA stay constant

Answer 35

2 purines are always joined by a hydrogen bond to a pyrimidine

Question 36

what are transcriptional regulators

Answer 36

proteins that bind to regulatory sequences at gene promoters on DNA they stimulate or inhibit transcription by bending DNA

Question 37

what are restriction endonucleases

Answer 37

enzymes that cut DNA at specific palindromic sequences cut DNA at sequences 6-10 base pairs used in bacteria to protect against viruses

Question 38

what is process of semi-conservative replication

Answer 38

1. DNA helicase breaks H bonds between base pairs separating strands and forming a replication bubble containing 2 replication forks 2. 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 3. primerase adds primers to the 3' end of the template and DNA polymerase adds nucleotides

Question 39

what is the leading strand of DNA

Answer 39

DNA replicated towards the replication fork and continues without breaks

Question 40

what is the lagging strand of DNA

Answer 40

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

Question 41

what are telomeres in DNA

Answer 41

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

Question 42

what does the cell theory suggest

Answer 42

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

Question 43

why are non-polar amino acid side chains found in the interior of globular proteins

Answer 43

they are hydrophobic so don't interact with polar water molecules outside the protein

Question 44

what are phage ghosts in bacteriophages

Answer 44

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

Question 45

how was bacteriophage genetic material observed

Answer 45

1. bacteriophage was grown in a 32P and 35S medium to radioactively label the DNA and protein in the phage ghost separately 2. the bacteriophage infected unlabelled bacteria and only the nucleic acid entered the host cells 3. the infected host cells were blended to remove phage ghosts and centrifuged to produce a pellet containing bacteria and supernatant containing phage ghosts 4. the pellet contained labelled DNA showing DNA is injected into the host cell for phage reproduction