bio paper 1 module 2

Question 1

Describe the structure of ATP and ADP

Answer 1

-phosphorylated nucleotides
-nucleotide derivative of adenine
-ATP has 3 inorganic (tri) phosphate groups
-ADP only has 2 (di)

Question 2

Describe the structure of DNA

Answer 2

-molecule twists to form double helix of 2 deoxyribose polynucleotide strands (2 sugar phosphate backbones)
-H bonds form between complimentary base pairs on strands that run antiparallel

Question 3

Identify features of the genetic code

Answer 3

-non-overlapping: each triplet is only read once
-degenerate: more than one triplet codes for the same amino acid
-universal: same bases and sequences used by all species

Question 4

What does transcription produce and where does it occur?

Answer 4

-produces mRNA
-occurs in nucleus

Question 5

Outline the process of transcription

Answer 5

-RNA polymerase binds to promoter region of gene
-section of DNA uncoils into 2 strands with exposed bases. antisense strand acts as a template
-free nucleotides are attracted to their complimentary bases
-RNA polymerase joins adjacent nucleotides to form phosphodiester bonds

Question 6

What happens after a strand of DNA is transcribed?

Answer 6

-RNA polymerase detaches at terminator region
-H bonds reform and DNA rewinds
-splicing removes introns from pre-mRNA in eukaryotic cells
-mRNA moves out of the nucleus via the nuclear pores and attaches to a ribosome

Question 7

What does translation produce and where does it occur?

Answer 7

-produces proteins
-occurs in cytoplasm on ribosomes (which are made of proteins and rRNA

Question 8

Outline the process of translation

Answer 8

-ribosome moves along mRNA until start codon
-tRNA anticodon attaches to complimentary bases on mRNA
-condensation reactions between amino acids and tRNA form peptide bonds, requires energy from ATP hydrolysis
-process continues to form polypeptide chain until stop codon is reaches

Question 9

Explain the induced fit model of enzyme action

Answer 9

-shape of active site is not directly complimentary to substrate + is flexible
-conformational change enables ES complexes to form when substrate adsorbs
-this puts strain on substrate bonds, lowering activation energy
-bonds in enzyme product complex are weak so product desorbs

Question 10

Explain the lock and key model of enzyme action

Answer 10

-suggests that active site has a rigid shape determined by tertiary structure so only complimentary to 1 substrate
-formation of ES complex lowers activation energy
-bonds in enzyme product complex are weak so product desorbs

Question 11

How does substrate/enzyme conc affect rate of reaction

Answer 11

-rate increases proportionally to substrate conc
-rate levels off when maimum no. of ES complexes form at any given time

Question 12

How does temp affect the rate of enzyme-controlled reactions?

Answer 12

-rate increases as KE increases and peaks at optimum temp
-above optimum ionic + H bonds in tertiary structure break= active site no longer complimentary to substrate= denatured

Question 13

Equation for Q10

Answer 13

R2/R1

Question 14

How does pH affect rate of reaction?

Answer 14

-enzymes has a narrow optimum pH range
-outside range H+/OH- ions interact with H-bonds + ionic bonds in tertiary structure= denature

Question 15

What are inactive precursors?

Answer 15

-to prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors e.g. proteases
-one part of precursor acts as an inhibitor. ES complexes form when it is removed

Question 16

Suggest how a student could produce a desired conc of solution from a stock solution

Answer 16

Question 17

Outline what happens during prophase

Answer 17

1.chromosomes condense becoming visible (X shaped)
2.centrioles move to opposite poles of cells (animal cells) + mitotic spindle forms
3.nuclear envelope + nucleolus break down= chromosomes free in cytoplasm

Question 18

Outline what happens during metaphase

Answer 18

sister chromatids line up at cell equator attached to mitotic spindle by centromeres

Question 19

Outline what happens during anaphase

Answer 19

Requires energy from ATP hydrolysis
1.spindle fibres contract= centromeres divide
2.sister chromatids separate into 2 distinct chromosomes + pulled to opposite poles of cell
3. spindle fibres break down

Question 20

Outline what happens during telophase

Answer 20

1.chromosomes de-condense becoming invisible again
2.new nuclear envelopes form around each set of chromosomes= 2 new nuclei each with 1 copy of each chromosome

Question 21

How is the cell cycle regulated?

Answer 21

checkpoints regulated by cell signalling proteins ensure damaged cells do not progress to next stage of cycle

Question 22

What happens during meiosis I?

Answer 22

1.homologous chromosomes pair to form bivalents
2.crossing over (exchange of sections of genetic material occurs at chiasmata
3.cell divides into 2. homologous chromosomes separate randomly. each cell contains either maternal or paternal copy

Question 23

What are homologous chromosomes?

Answer 23

-pair of chromosomes with genes at same locus.
-1 maternal + 1 paternal
-some alleles may be same while others are different

Question 24

What happens during meiosis II?

Answer 24

1. independent segregation of sister chromatids
   2.each cell divides again producing 4 haploid cells

Question 25

What happens during prophase I of meiosis?

Answer 25

-DNA condenses and becomes visible as chromosomes- 2 sister chromatids
-chromosomes are arranged in homologous pairs (bivalents)
-crossing over of non-sister chromatids may occur at chiasmata
-centrioles to opposite side + spindle forms
-nuclear envelope + nucleolus breaks down

Question 26

What happens during metaphase I of meisois?

Answer 26

-bivalents line up along equator of cell with spindle attached to centromeres
-independent assortment occurs

Question 27

What happens during Anaphase I of meiosis?

Answer 27

-homologous chromosomes are separated as microtubules pull whole chromosomes to opposite ends of spindle
-centromeres do not divide

Question 28

What happens during telophase I of meiosis?

Answer 28

-chromosomes arrive at opposite poles
-spindle fibres start to break down
-nuclear envelope form around 2 groups of chromosomes

Question 29

What happens during prophase II of meiosis I?

Answer 29

-nuclear envelope breaks down and chromosome condense
-spindle forms at right angle to old one

Question 30

What happens during metaphase II of meiosis?

Answer 30

chromosomes line up along equator of spindle

Question 31

What happens during anaphase II of meiosis?

Answer 31

-centromeres divide and individual chromatids are pulled to opposite poles
-creates 4 groups of chromosomes that are haploid

Question 32

What happens during telophase II of meiosis?

Answer 32

nuclear membranes form around each group of chromosomes

Question 33

Suggest some uses of stem cells
(4)

Answer 33

-repair of damaged tissue
-drug testing on artificially grown tissues
-treating neurological diseases e.g. alzheimers + parkinsons
-researching developmental biology e.g. formation of embryos

Question 34

What type of blood cells are RBC’s and neutrophils?

Answer 34

-rbcs= erythrocytes
-neutrophils= leucocytes

Question 35

How do specialised cells in the blood form?

Answer 35

-multi potent stem cells in bone marrow differentiate into:
-erythrocytes which has short life span and can not undergo mitosis since they have no nucleus
-leucocytes including neutrophils

Question 36

Describe squamous epithelilal cells

Answer 36

-provides an outer layer e.g. on blood vessels
-consists of a single layer of flattened cells on basement membrane which forms thin cross section
-this reduces diffusion distance
-permeable= allows for easy diffusion of gases

Question 37

Describe ciliated epithelilial cells

Answer 37

-move substances across surface of tissue
-have cilia=move in coordinated way to shift material along surface of epithelium tissue
-goblet cells= secrete mucus which helps trap dirt etc.

Question 38

Describe cartilage tissue

Answer 38

-provides support
-strong + flexible found e.g. in trachea
-rings support trachea ensuring it stays open

Question 39

Describe muscle cells

Answer 39

-contraction for movement
-3 types:skeletal, smooth + cardiac
-all have layers of protein filaments which can slide= muscle contraction
-high density of mitochondria for respiration in muscle contraction
-skeletal can fuse together during development to form multinucleated cells that contract in unison
-image=skeletal

Question 40

Describe xylem tissue

Answer 40

-vessel elements: lignified secondary walls for mechanical strength + waterproofing. perforated end walls for rapid water flow
-tracheids: tapered ends for close packing; pits for lateral water movement; no cytoplasm or nucleus

Question 41

Describe additional cell types in xylem tissue

Answer 41

-xylem parenchyma: packing tissue with thin walls transmit turgidity
-sclereids
-sclerenchyma fibres: heavily lignified to withstand negative pressure

Question 42

Name the 3 types of muscle in the body and where they are located

Answer 42

-cardiac: only found in heart
-smooth: walls of blood vessels + intestines
-skeletal: attached to incompressible skeleton by tendons

Question 43

Describe the structure of phloem tissue

Answer 43

-sieve tube elements: transport sucrose in the dissolved form of sap
-companion cells: involved in ATP production for active loading of sucrose into sieve tubes
-plasmodesmata: gaps between cell walls where cytoplasm links, allowing substances to flow

Question 44

Describe a guard cell

Answer 44

-form stoma
-when turgid stoma opens, when flaccid stoma closes
-walls thickened by spirals of cellulose