topic 2 - genes and health Flashcards
3 factors that increase rate of diffusion
- large surface area to volume ratio
- thin surfaces
- steep concentration gradient: greater difference in number of molecules passing in the two directions means a faster rate of diffusion
- temperature: more kinetic energy, thus molecules move faster
how are lungs adapted for gas exchange?
- lots of alveoli increases surface area
- alveoli one cell thick - reduces diffusion distance
- rich blood supply to maintain conc gradient
describe cell membrane structure
“fluid mosaic” structure
- phospholipid molecules form a bilayer
- phospholipid molecule contains a head containing the phosphate group (hydrophilic) and a tail made of two fatty acids (hydrophobic).
- hydrophobic heads face in meaning the membrane does not allow water soluble substances to pass
- protein molecules scattered through
- some proteins have a polysaccharide - glycoproteins
- some lipids have the same -glycolipids
- cholesterol makes membrane more rigid
diffusion definition
the net movement of molecules from a region of high conc to a region of low conc down a conc gradient
- passive
facilitated diffusion
- explain carrier and channel proteins
carrier proteins: move large molecules into and out of cell.
1. a large molecule attaches to carrier in membrane. 2. protein changes shape. 3. molecule released on opposite side
channel: form pores in the membrane so ions can diffuse through. each type of channel protein has a specific shape
osmosis defintion
the net movement of water molecules from a solution with high water potential to low
- continues until isotonic
active transport explain
- substances are moved against a conc gradient
- energy in form of ATP required
explain endocytosis
- some molecules are too large to be taken in by carrier proteins. instead a cell can surround substance with a section of its membrane and form a vesicle inside the cell. requires ATP
explain exocytosis
substances need to be released.
vesicles containing these substances pinch off from sacs of golgi apparatus and move towards membrane.
- vesicles fuse with membrane and release contents
- uses ATP
proteins monomer
amino acids
bond that joins amino acids
peptide bond
(this is covalent)
explain primary structure
- define
- explain how this occurs
- the sequence of amino acids in a polypeptide chain
- two amino acids join in a condensation reaction to form a dipeptide
explain secondary structure
- 2D arrangement of the chain of amino acids
- chain may twist to form an alpha helix. hydrogen bonds form between slightly neg carboxylic acid and slightly pos amine group
- chain may fold back on itself and link together with hydrogen bonds to form a beta pleated sheet. each bond is weak but there are many so structure is stable
explain tertiary structure
- 3D folding of the secondary structure
- shape is determined by type of bonding present: hydrogen bonding, ionic and disulphide bridges
- chemical bonds maintain structure
-disulphide bonds are strong but sensitive to changes in pH
explain quaternary structure
- 3D arrangement of more than one polypeptide
globular proteins
- properties and structure
- example
- polypeptide chain folded into compact, spherical shape
- soluble due to hydrophilic side chains so easily transported
- egs include enzymes and antibodies
- HAEMOGLOBIN:
- consists of 4 beta polypeptide chains and a haem group.
- 4 polypeptide chains are held together with disulphide bonds
- water soluble
- conjugated protein as associated with another chemical group
fibrous proteins
- structure and properties
- example
- long parallel polypeptides
- can be cross linked for additional strength
- insoluble due to hydrophobic R groups
- used for structure
- strong
- COLLAGEN:
- three polypeptide chains wound together and held by H bonds
- each strand cross links for strength
- strands are staggered to avoid weak points
- stable protein due to high proportion of proline and hydroxyproline amino acids present.
- strong due to hydrogen and covalent bonds
enzymes definition
-globular proteins that speed up chemical reactions by acting as a biological catalyst
lock and key theory
- specific substrate molecule fits into active site of enzyme
- substrate forms temporary bonds with active site to form enzyme substrate complex
- products are released
induced fit theory
- when substrate enters active site, enzyme changes shape slightly
- products formed and released
how do enzyme properties relate to tertiary structure
- enzymes are very specific, they only catalyse one reaction as only one complementary substrate fits active site
- active site is determined by primary structure
- each enzyme has different tertiary structure and thus a different active site
- if tertiary structure changes, active site changes and substrate wont fit
what is tertiary structure altered by
- pH and temperature
how does temp affect enzyme action
- increase in kinetic energy means molecules move faster, more successful collisions
- after optimum temp (40 degrees) H bonds break, and active site changes shape
- substrate no longer fits
- tertiary structure is disrupted: enzyme and active site denatures
how does pH affect enzyme action
- change in pH changes H and ionic bonds on amino acids
- active site alters and substrate does not fit
- bonds holding tertiary structure break and enzyme changes shape and denatures
how does enzyme conc affect enzyme action
how does substrate conc affect enzyme action
- more enzyme molecules = more active sites and more successful collisions. this increases rate of reaction
- if substrate is limited adding more enzymes does nothing
- the higher the conc, the faster the reaction due to collisions. at “saturation point” all active sites are full so it no longer has an effect
competitive inhibitors
- binds to enzyme in active site as shape is similar to substrate
- occupies active site
non- competitive inhibitors
- binds to enzyme in allosteric site which changes shape of enzyme so substrate cannot fit
two stages of protein synthesis
transcription and translation
describe transcription
A MOLECULE OF mRNA IS MADE IN NUCLEUS
1. hydrogen bonds break between complementary bases and DNA uncoils into two strands
2. one DNA strand is used as a template to make mRNA. this is the antisense strand
3. free nucleotides line up by complementary base pairing and adjacent nucleotides are joined with phosphodiester bonds. forming mRNA
4. mRNA moves out nucleus through pore and attaches to a ribosome
name the three components of nucleotides
- pentose sugar
- phosphate group
- organic base
describe DNA structure
- double stranded
- made up of deoxyribose mononucleotides linked through condensation reactions
- possible bases are adenine, cystine, guanine and thymine
- c pairs with g
- a pairs with t
how does DNA form a double stranded helix
- bases form hydrogen bonds with each other holding two strands together
- stacking of many mononucleotides results in helix shape
describe RNA structure
- single stranded
- made up of many mononucleotides linked via condensation reactions
- possible bases are adenine, cystine, guanine and uracil
- c pairs with g
- a pairs with u
identify four features of the genetic code
- triplet of bases codes for a particular amino acid
- non overlapping : each base is only read once so the adjacent codons do not overlap
- degenerate = more than one triplet codes for the same amino acid
- universal: almost every organism uses the same code, the same triplet codes code for the same amino acids in all living things
gene definition
a sequence of bases on a DNA molecule that codes for a specific sequence of amino acids in a polypeptide chain
describe translation
- mRNA goes to ribosome which reads sequence in codons recognised by anti codons found on tRNA which carries amino acids which join via peptide bonds to form polypeptides until a stop codon is reached
MRCATAPP
Explain how a change of one amino acid could lead to a change in the
structure and properties of the haemoglobin protein.
different {sequence of amino acids / primary structure} (1)
• (a different amino acid will have a) different R group (1)
• (therefore) {secondary / tertiary / quaternary} structure
will change (1)
• (due to a) change in a named bond (holding molecule in its
three-dimensional shape) (1)
• (haemoglobin) may not bond to oxygen (1)
Explain how the structure of a phospholipid molecule contributes to the
partial permeability of a cell surface membrane.
(phospholipid molecule) contains a {polar / hydrophilic}
(phosphate) head and {non-polar / hydrophobic} fatty acid
chains (1)
• allows {fat-soluble/non-polar} molecules to pass through (the
membrane) (1)
• {polar / ionic} molecules cannot pass through (phospholipid
bilayer) (1)
compare and contrast endo and exocytosis
- both involve ATP
- both involve vesicles
- one leaves one enters
Describe how mRNA is synthesised at a template strand of DNA.
(RNA) nucleotides align with complementary bases (on DNA) (1)
• RNA nucleotides joined together by {RNA polymerase /
phosphodiester bonds} (1)
explain the steps of semi conservative DNA replication
- double helix unwinds and hydrogen bonds break between complementary bases, catalysed by DNA helicase, separating the two strands
- one of the strands is used as a template and complementary base pairing occurs
- adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions