Term 1Revision

Biology 12

Cell membranesSketch a typical cell membrane according to the Fluid Mosaic model

Describe the roles of:• Phospholipids

• Proteins

• Carbohydrates

CellsSketch a typical cell membrane according to the Fluid Mosaic model .

Describe the roles of:Phospholipids = A – waterproof, flexible layer, that lets in small particles

Proteins = B – provides channels for larger particles (facilitated diffusions), acts as pumps (active transport), acts as receptor sites

Carbohydrates = C - acts as receptor sites

A

B

C

Exchange of material

Show the movements of water and ions that would occur in both these cases

Distilled water Sea water

Exchange of material

Show the movements of water and ions that would occur in both these cases

Distilled water Sea water

Water moves in

Water moves out Ions move inIons move out

TEE Extended answer 2003 36a

Genetic information is stored in molecules of DNA. Using labelled diagrams describe the structure of DNA at the level of major

components and describe how it carries genetic information

Extended answer 2003 36a) Genetic information is stored in molecules of DNA. Using labelled diagrams describe the structure of DNA at the level of major components

and describe how it carries genetic informationOne mark/dot point in answers below unless otherwise indicated. Maximum 10

marks/question.

Diagram – showing nitrogenous base pairs - A T, C G, and sugar phosphate backbone• one mark for nitrogenous pairs label on the figure, 2 marks for sugar phosphate

backbone label(3 marks total)• nucleotides• double helix• one mark for correct basic structure in the figure• name bases (one mark for naming all 4)• indicate pairing (each correct pairing = one mark)• sequence of bases codes for amino acid structure• triplet code/codons• relationship to amino acidsThe information is carried within the DNA by the sequence of base pairs. Each segment

of 3 nucleotides codes for one amino acid & is called a codonThis information is copied to mRNA in the nucleus and carried to the ribosomes,

determining which proteins are made

Structure of DNA

Structure of DNAnucleotides

Adenine

Guanine

sugar

phosphate

Protein synthesis• Transcription• Translation• Codon• Anticodon• t-RNA• m-RNA• r-RNA• Protein• Amino acid

Protein synthesis• Transcription – copying of RNA from DNA• Translation – reading of mRNA at ribosome• Codon – 3 nucleotide section on mRNA that codes

for an amino acid• Anticodon - 3 nucleotide section on tRNA that

matches codon, tRNA brings the right amino acid• t-RNA – carries amino acid• m-RNA – codes for sequence of amino acids• r-RNA – makes up ribosomes• Protein – long chain of amino acids (end product)• Amino acid – unit that is put together to make

protein

DNA replication• Occurs in • One set of enzymes • Another set of enzymes• Nucleotides match up by the

(C , A )

• The end result is joined at a point called the

DNA replication• Occurs in nucleus • One set of enzymes splits DNA• Another set of enzymes adds

new nucleotides• Nucleotides match up by the

base pairing rule (C - G, A - T )

• The end result is 2 strands (chromatids) joined at a point called the centromere

Stages of mitosis

Stages of mitosis

• Interphase – normal cell metabolism & growth, DNA replication

• Prophase – nucleus disappears, spindle forms, chromosomes condense & become visible

• Metaphase – chromosomes line up on equator• Anaphase – chromatids split & move to opposite

ends of cell• Telophase – new nuclei form, cytoplasm divides

to form 2 new cells• Interphase - normal cell metabolism & growth

Identify the stages of mitosis

Identify the stages of mitosis

telophase

anaphase

metaphase

interphase

prophase

TEE - Extended answer 2002 36dMost genes in the body carry information about the structure of enzymes,

highlighting the importance of enzymes to cellular function.

Describe the functions of enzymes in cells and explain why enzymes are so specific in their action.

Discuss the factors that affect enzyme activity, and describe their effects

Extended answer 2002 36d)Most genes in the body carry information about the structure of enzymes, highlighting the

importance of enzymes to cellular function.Describe the functions of enzymes in cells and explain why enzymes are so specific in their

action.Functions of Enzymes (max 7 marks):• catalysis • speed up reactions• reduce activation energy • synthesis / anabolism & example• digestion / catabolism & example • energy production & example• control of chemical pathways / energy productionEnzyme Specificity:• Caused by active site / 3D shape• Formation of enzyme – substrate complex / lock & key model• Good diagram of lock & key model• Enzymes work within narrow pH ranges• Enzymes work within narrow temperature rangesDiscuss the factors that affect enzyme activity, and describe their effects• Increasing temperature increases activity, unless it gets too hot and the enzyme is

destroyed• Changing pH alters shape of enzyme reduces activity• Increasing substrate concentration increases activity (up to maximum)• Increasing enzyme concentration increases activity (up to maximum)• Decreasing product concentration decreases activity• Increasing cofactor concentration increases activity (up to maximum)• Presence of inhibitors decreases activity