A Level Biology Topic 2

Front 1

Phospholipids

Back 1

- phosphate head (hydrophilic)

- 2 fatty acid tails (hydrophobic)

Hint 1

Front 2

Incomplete dominance

Back 2

When the dominant allele isn’t completely shown over the recessive allele So BOTH alleles are expressed

Front 3

DNA

Back 3

-double helix

- phosphate grp, deoxyribose, nitrogenous base

- complementary base pairing of A&T (2 h-bonds) & G&C (3 h-bonds)

- 2 antiparallel strands

Front 4

How is the mammalian heart adapted for gas exchange?

Back 4

- alveoli have a large SA:V ratio

- constant supply of oxygen to the lungs > maintains steep diffusion gradient

- alveoli have thin walls (one cell thick) > diffusion is quick due to SHORT diffusion pathway

- network of capillaries provides a constant supply of (deoxygenated) blood

Front 5

Sense strand/coding

Back 5

mRNA

Hint 5

Sara May Cry

Front 6

Antisense/template strand

Back 6

DNA

Hint 6

And Dad Too

Front 7

Fibrous protein

Back 7

- structural protein (e.g. keratin)

- thin, long polypeptide chains

- insoluble

- hydrophobic chains on outside

- little tertiary and no quaternary structure

Front 8

Globular protein

Back 8

- functional protein (e.g. amylase)

- round, compact, coiled up

- soluble

- hydrophilic chains on outside > all around the GLOBE ppl want to b lovedd 😂

- have tetiary and quaternary structure

Front 9

Role of tRNA

Back 9

- brings CORRECT/SPECIFIC amino acid to the ribosome

- involved in translation

- peptide bond forms

- specific anticodon has complementary base pairing to codon + holds amino acid in place

Front 10

Role of mRNA

Back 10

- exact replica of DNA

- acts as a template during translation (contains instructions)

- leaves nucleus to go to ribosome

Front 11

Endocytosis

Back 11

- atp is used

- molecules that are TOO large can be taken into the cell

- substance merged with cell membrane

- a vesicle forms containing ingested substance

Front 12

Exocytosis

Back 12

- atp is used

- vesicle pinches off of Golgi apparatus

- moves towards cell membrane

- merged with cell membrane

- substance released outside the membrane

Front 13

What is a glycoprotein

Back 13

Protein + carbohydrate

Front 14

What is a glycolipid

Back 14

Lipid + carbohydrate

Front 15

Cell membrane (5 marks)

Back 15

- phospholipid bilayer

- arrangement = hydrophobic tails facing inwards (fatty acids) & hydrophilic heads facing outwards (phosphate)

- glycolipid/ glycoproteins > help stabilise the membrane structure by forming h-bonds with water molecules around cell

- channel, carrier proteins > both involved in facilitated diffusion (&/ active transport)

- intrinsic/extrinsic proteins

- cholesterol > helps cell maintain rigidity By forming bonds between the phospholipids

Front 16

Osmosis

Back 16

- down a conc gradient

- across a semi permeable membrane

- movement of water molecules from place of high conc to place of low conc

- DIFFUSION therefore PASSIVE

Front 17

Carrier proteins

Back 17

- molecule attaches to BINDING SITE

- protein changes shape

- releases molecule on other side

-involved in active transport & facilitated diffusion

- LARGE MOLECULES

- high specificity

Front 18

Channel protein

Back 18

- ions let through

- not repelled by hydrophobic tails

- facilitated diffusion so PASSIVE

- down a conc grad

- high specificity

Front 19

Active transport

Back 19

- requires energy in the form of ATP

- ATP hydrolysed = energy releases > causes carrier protein to change shape

- against a conc grad (from a place of low to high conc)

- ions & large molecules

- CARRIER PROTEIN

- high specificity

Front 20

Investigating cell membrane structure practical (4 marks)

Back 20

- IV = temp of water baths e.g. 10,20,30,40,50,60 degrees

- control variable = same size beetroot, age of beetroot, type of beetroot

- use of colorimeter > absorbance of light will show which sample was most permeable

- repeats > to allow calculation of means

Front 21

Why does increasing temperature increase cell permeability ? (Between 0-45 degrees)

Back 21

phospholipid bilayer becomes more fluid > kinetic energy

Front 22

Why does increasing alcohol concentration increase membrane permeability?

Back 22

Alcohol dissolves lipids in the cell membrane > less rigid > more permeable

Front 23

What joins amino acids together ? Between what groups?

Back 23

Peptide bond

Between the amine & carboxylate grps

Front 24

What reaction results in peptide bond formation?

Back 24

Condensation

Front 25

Primary structure bonding

Back 25

Peptide bonds (between pairs of amino acids)

Front 26

Secondary structure bonding

Back 26

H bonds (between amino acids within a chain)

Front 27

Tertiary structure bonding

Back 27

- Ionic (attractions between -ve & +ve parts of the molecule > folding)

- di sulfide (between sulfurs in molecules containing cysteine; an amino acid > folding )

- hydrogen bonds (> folding)

- hydrophobic/phillic interactions ( > folding)

(Between amino acids within a polypeptide chain)

Front 28

Lock & key model

Back 28

Specific active site complementary to specific substrate

Front 29

Induced fit

Back 29

Substrate changes shape of active site slightly to better fit it

Front 30

What is mRNA made of?

Back 30

Ribose (pentose sugar)

Phosphate group

Nitrogenous base

Bases A&U + G&C

Front 31

Bond between phosphate grp & pentose sugar

Back 31

Phosphodiester bond

Front 32

Where does Transcription occur

Back 32

In nucleus

Front 33

Where does Translation occur

Back 33

In ribosome

Front 34

Degenerate

Back 34

More than one triplet codes for the same amino acid

Front 35

Non -overlapping

Back 35

Bases read 3 at a time (in sequence)

Each base read once > not repeated

Front 36

Transcription (process)

Back 36

1) DNA helicase unzips DNA (break h-bonds) > becomes single stranded (coding strand)

2) free mononucleotide mRNA bases attach to DNA strand (complementary base pairing)

3) RNA polymerase create phosphodiester bonds between mononucletides

4) mRNA detaches from DNA

5) coding strand of mRNA leaves nucleus > ribosome

Hint 36

TransCription so Coding strand!

Front 37

Translation

Back 37

1) mRNA attaches to a ribosome + tRNA brings specific amino acid to ribosome

2) anticodon of tRNA attaches to codon of mRNA (holds amino acid in place) due to complementary base pairings

3) peptide bond forms between amino acids > polypeptide (protein) forms

4) tRNA leaves to pick up another amino acid

Front 38

Replication of DNA (process)

Back 38

1) DNA helicase unwinds DNA (breaks h-bond between bases) into 2 separate strands

2) free DNA mononucleotides join & form h-bonds with the bases (complementary base pairing)

3) DNA polymerase creates phosphodiester bonds between deoxyribose & phosphate + checks DNA sequence for errors

4) 1 new strand & 1 original strand (x2) > DNA replication is semi conservative

Front 39

What reaction joins a pentose sugar and phosphate grp?

Back 39

Condensation

Front 40

Meselson & Stahl (key points about them)

Back 40

- used 2 isotopes of nitrogen

- grew E.coli in nitrogen

- centrifuged to see where DNA was (heavy = near bottom, light = near top)

- grown in light N > when centrifuged DNA showed up in the middle of the test tube

- semi conservative replication

Front 41

Why are mutations bad?

Back 41

Different primary structure > different 3D structure > changes function of protein

Front 42

Non functional CFTR channel...

Back 42

- chloride ion channel x work

- chloride ions x move out of cell

- less water moves out by osmosis

- sodium ions x move out of cell

- sticky, thick mucus

Front 43

CF respiratory system

Back 43

- cilia find it difficult to move sticky mucus

- lung infection ^ likely as bacteria in mucus not flushed out

- hard to breathe > mucus around alveoli = less efficient gas exchange

Front 44

CF digestive system

Back 44

- cysts in PANCREAS > inhibit the production of digestive enzymes

- thick mucus along pancreatic duct stops digestive enzymes getting to the small intestine

- less DIGESTION > less energy

- lining of small intestine is thick > inhibits absorption of nutrients

Front 45

CF reproductive system

Back 45

Females:

sticky cervical mucus stops sperm travelling to egg

Males:

sticky mucus in vas deferons/ speed duct from testes to penis > stops sperm swimming penis

Front 46

Ethical issues with pre natal genetic testing (e.g. amnioscentesis)

Back 46

- chance of miscarriage

- false positive > lead to abortion for NO reason

- unethical as it has a right to life

- Against the values & beliefs of the parents

Front 47

Amniocentesis

Back 47

- after CVS

- 1% risk of miscarriage

- needle into abdomen > fetal/placental cells (from amniotic fluid)

- 15-20 weeks

Front 48

Chorionic Villus Sampling

Back 48

- before amniocentesis

- 1-2% miscarriage

- needle to abdomen > fetal cells (from chorionic villus)

- 11-14 weeks

Front 49

PGD

Back 49

Embryos tested for genetic disorder > healthy ones implanted into mother

Front 50

CF buzzwords

Back 50

- sticky, thick mucus

- osmosis

- cilia

- CFTR channel protein

- chloride ions

Front 51

Cell membrane permeability increasing temp (>45 degrees)

Back 51

Membrane melts + proteins deform = more permeable

Front 52

Permeability of cell membrane decreasing temp (below 0 degrees)

Back 52

proteins deform > increases permeability of membrane

Front 53

Quaternary structure bonding

Back 53

Further bonds between polypeptide chains

Front 54

Primary structure (define)

Back 54

Sequence of amino acids in the polypeptide chain

Front 55

Secondary structure (describe)

Back 55

- Coils up into an alpha helix

- Folds in a beta pleated sheet

Front 56

Tertiary structure (describe)

Back 56

- Bonding in R grp = further coiled & folded

- decides proteins 3D shape

- bonds between different parts of the polypeptide chain

Front 57

Quaternary structure (describe)

Back 57

Bonds between different polypeptides (that make up the protein)

Front 58

Why is the 3D structure of a protein important

Back 58

Folding due to bonding > decides it’s function

Front 59

Define an enzyme

Back 59

- Speeds up the rate of reaction

- lowers the activation energy

Front 60

What factors effect rate of reaction in an enzyme? How?

Back 60

- enzyme concentration > less enzymes = less collisions = enzyme substrate complexes form

- substrate concentration > less substrates = lower chance of collision so less likelihood of enzyme substrate complexes forming

- temperature: too high = enzyme becomes denatured too low = less collisions > rate of reaction is veryyy slow

- pH: too low/high = change active site of enzyme > enzyme becomes denatured

Front 61

Genetic screening (identifying carriers)

Ethical debates

Back 61

- distressing

- false +ves > believe u have the disease when u do not

- life insurance & employment companies leading to discrimination

- more informed decision

- medication can be prescribed early > longer life?

Front 62

IVF

Ethical debates

Back 62

- stops abortion

- baby won’t have genetic disorder

- designer babies

- false results

Front 63

Core practical: measuring rate of reaction using an enzyme

(How fast product is made)

Back 63

- place hydrogen peroxide and catalase into a conical flask (attached to a gas syringe)

- place the bung on top

- record the volume of oxygen produced every 10 seconds for a minute (10,20,30,40,50,60)

- use a stopwatch

- IV: concentration of enzyme e.g. 0.1,0.2,0.3, 0.4, 0.5

- control variable: volume of enzyme solution, temperature of enzyme solution

- repeats (at least 3 times) & find a mean

Front 64

How do you calculate initial rate of reaction?

Back 64

rate (gradient) at the start of the reaction

Front 65

Describe diffusion (3)

Back 65

- passive > no energy

- from high to low conc > down conc grad

- small uncharged molecules

Front 66

What type of reaction joins amino acids together?

Back 66

Condensation

Front 67

What molecules are unable to pass through the cell membrane (& why)?

Back 67

• ionic molecules (carry both +ve AND -ve charge)

• large molecules

Hint 67

• Gases > non polar & small > pass through quickly

• SMALL polar molecules (+ve/-vely charged) > because small (pass through the gaps) > pass through slowly

• large non polar molecule > able to get through hydrophobic region > pass through slowly

Front 68

Why does the cell membrane let through these particular molecules?

Back 68

Small > phospholipids are packed close together

Non polar > hydrophobic tails

Front 69

When does transcription start

Back 69

When RNA polymerase attaches to the (primer on) DNA at the start of a gene (start codon)

Front 70

Monohybrid inheritance

Back 70

The inheritance of a single characteristic controlled by different alleles

Front 71

Gene

Back 71

A sequence of bases of DNA coding for a specific protein (which results in a characteristic/phenotype)

Front 72

Allele

Back 72

Different variants of a gene. Found on the same locus of a chromosome.

Front 73

Genotype

Back 73

The entire set of genes in a cell. All alleles present at the locus of (or closely linked loci).

Front 74

Phenotype

Back 74

Observable characteristics displayed by an organism

Front 75

What is high water potential

Back 75

High concentration of water (in that region)

Front 76

What is the difference between polar molecules and ions

Back 76

Polar molecules - molecules have a ‘partial’ charge, e.g. are relatively +ve/-ve, as charge is not evenly distributed within the molecule

Ions - ‘complete’ charge which is either -ve/ +ve