Unit 4 - Variation Y12

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What are the 3 parts making up ATP?

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  • organic base

  • Ribose sugar

  • Phosphate groups

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How does ATP store energy?

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By its three phosphate bonds (but the bonds have are unstable so they’re easily broken)

They release lots of energy when bonds broken

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90 Terms

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What are the 3 parts making up ATP?

  • organic base

  • Ribose sugar

  • Phosphate groups

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How does ATP store energy?

By its three phosphate bonds (but the bonds have are unstable so they’re easily broken)

They release lots of energy when bonds broken

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What are the uses of ATP?

  • synthesis of protein , DNA , RNA , fat , carbohydrates

  • Active transport of ions and metabolites

  • Movement

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How does ATP work?

  1. ATP diffused to the part of the cell that needs energy

  2. ATP broken down into ADP by hydrolysis reactions breaking the phosphate group bonds to release energy

  3. This hydrolysis reaction is catalyses by the enzyme ATP hydrolase

  4. The released inorganic phosphate can be added to other compounds

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Where is ATP made?

It is made continuously in the mitochondria (in the inner membrane) of cells when required

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Why is ATP a better source of energy in cells than glucose?

  1. ATP only uses a single simple reaction to release energy whereas glucose uses a complex serious of enzyme controlled reactions

  2. ATP doesn’t leave the cell, meaning it always has a constant supply of energy

  3. ATP contains a small manageable amount of energy so no energy is lost as heat

  4. ATP is a small soluble molecule that can be easily transported around the cell

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What is the structure of DNA?

a double helix with two polynucleotide chains held together by hydrogen bonds

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What is the role of DNA?

it contains all the DNA needed to make a new copy of the cell and to control the activities of the cell

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What is the role of RNA?

it transfers gentic information from the DNA to the ribosomes

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What is the role of the rough endoplasmic recticulum?

a series of thin intricate channels formed by a phospholipid membrane and it continuous with the nuclear membrane

  • so, materials can be moved easily through the channels between each membrane

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What is the role of the smooth endoplasmic recticulum?

a tubular phospholipid membrane where lipids are synthesised and processed due to the ribosomes on the SER’s surface

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What is the role of the golgi apparatus?

to take enzymes and other synthesised proteins and package them into membrane bound vesicles where they are then transported to other parts of the cell

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What are the monomers making up DNA called?

nucleotides

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What do nucleotides consist of?

  1. phosphate group

  2. pentose sugar called deoxyribose

  3. organic nitrogenous base

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What are the 4 nitrogenous bases?

  • adenine (A)

  • thymine (T)

  • cytosine (C)

  • guanine (G)

A and T bind by 2 hydrogen bonds

C and G bind by 3 hydrogen bonds

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What does DNA and RNA stand for?

DNA - deoxyribonucleic acid

RNA - ribonucleic acid

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What are ribosomes formed from?

RNA and proteins

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What is the Penrose sugar called in DNA compared to RNA?

DNA - deoxyribose

RNA - ribose

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What’s the difference in organic bases in RNA compared to DNA?

RNA has U (uracil) instead of Thymine which is in DNA

So, A + U bind and C + G bind

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What are the three forms of RNA?

  1. mRNA - several thousands nucleotides long (messenger RNA)

  2. tRNA - less than 100 nucleotides long (transfer RNA)

  3. rENA - several thousands nucleotides long (ribosomal RNA)

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What is difference in shape of RNA compared to DNA?

DNA is a double helix

RNA is single stranded

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What’s the purpose of RNA?

RNA transfers genetic information from DNA to the ribosomes

RNA is found in the cytoplasm

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What is the function of mRNA?

They are copied sections of DNA that can pass through the nuclear pores to reach ribosomes in the cytoplasm

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What is transcription?

It involved the synthesis of mRNA using the code on the sense strand part of the DNA

  1. DNA unwinds and hydrogen bonds between bases break

  2. A free nucleotide bonds to an exposed complementary base, creating pre-mRNA

  3. the mRNA is released and the DNA returns to a double helix

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How are the hydrogen bonds between the DNA bases broken?

Due to the enzymes DNA helicase where the region of the gene being transcribed is

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What are the complementary bases joined up by?

RNA polymerase from condensation reactions, forming phosphodiester bonds between the ribose sugar of one nucleotide and the phosphate group of the next

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What happens after transcription?

Splicing takes place - the removal of introns (useless parts of gene) and the exons joining together to form mRNA strands

After, the mRNA Then leaves the nucleus

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What is translation?

The process which the protein is assembled from the mRNA (happens in cytoplasm of cell)

Involved tRNA and rRNA

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What is the role of tRNA is translation?

Anticodons are linked to its complementary codon for the amino acid created from the mRNA

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What is the role of rRNA in translation?

  • the ribosomes link amino acids together in the order specified by the codons of mRNA to form polypeptide chains

  • Ribosomes consist of small (where mRNA binds and decoded) and large (amino acids get added) sub units

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How does translation work?

  1. mRNA moves into the cytoplasm and attached to a ribosome

  2. Anti codons in tRNA bind to vacant codons in the ribosome

  3. The attached amino acids (located at top of the tRNA) form a peptide bond

  4. as mRNA moves through ribosome, it releases the tRNA that aren’t bound to an amino acid and then the steps are repeated until the end of the mRNA

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What is rRNA?

They are the site of protein synthesis, made of protein and RNA in the nucleolus

They are free in the cytoplasm or attached to the RER

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What is a polysome?

When several ribosomes are attached to a single mRNA molecule

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What happens when gametes fuse?

  • a zygote is formed containing 46 chromosomes

  • Zygote grows into an adult by repeatedly dividing by mitosis

  • Eventually a ball of 100 cells are formed (a blastula) that aren’t yet differentiated

  • Chromosomes are still active and called stem cells

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What happens in the process of semi conservative replication?

  1. The enzyme DNA helicase breaks the hydrogen bonds between the 2 polynucleotide strands

  2. Free floating DNA nucleotides join to the exposed bases by the enzyme DNA polymerase, forming hydrogen bonds

  3. The active site of DNA polymerase is only complementary to the 3’ end of the new DNA strand

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Who are Watson and Crick?

They built the DNA modem to explain the unit of inheritance

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What are the three theories of replication?

  • Semi conservative

  • Conservative

  • Dispersive

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What is cell division needed for?

It is needed for growth

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What are the two types of cell division?

  • mitosis → where daughter cells are genetically identical to the parent cell

  • Meiosis → where each daughter cell contains half the number of chromosomes of the parent cell, leading to the production of gametes

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What organisms does mitosis and meiosis happen in?

Mitosis - in multicellular organisms for growth and repair and in unicellular organisms for asexual reproduction

Meiosis - all organisms that reproduce sexually

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What is the cell cycle?

The series of event involving the growth, replication and division of a eukaryotic cell

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What are the three stages of the cell cycle?

  1. Interphase including G1, S, G2

  2. Nuclear division (notification division of nucleus

  3. Cell division nitric cell division

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What are the stages of the cell cycle?

  1. GO phase - DNA is relaxed (chromatin) and not yet started to divide

  2. G1 phase - cell starts making proteins and organelles, growing larger

  3. S phase - chromosomes containing genetic code are copied

  4. G2 phase - cell checks DNA and prepares to start splitting into two cells

  5. M phase - cell splits into two new cells

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What are centrioles?

They are cylinder shaped cell structure made of microtubles and are involved in the organization of the spindle (where centromeres attach to)

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What are sister chromatids?

Copies of the same chromosome attached to the centromere

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What are the 4 phasers in the mitotic phase?

  1. Prophase → chromosomes become visible in nucleus, DNA been replicated so nuclear membrane breaks up and fibrous soundly forms from centrioles

  2. Metaphase → chromosomes attach to spindle by centromere, nuclear membrane has broken down

  3. Anaphase → sister chromatids separate and spindle fibres shorten causing chromatids to move to opposite poles of cell

  4. Telophase → spindle disintegrates, nuclear membrane forms and chromosomes unravel to become chromatin

  5. Cytokinesis → produces 2 daughter cells and cell membrane contracts to split apart cell into 2

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What is cancer?

A mutation in genes that cause uncontrolled cell growth and division

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How does chemotherapy treat cancer?

  • prevents the synthesis of the enzyme needed for DNA replication

  • This prevents the cell entering the S phase, causing it to die

  • Inhibits metaphase by altering the way spindle fibres work so no division of chromatids and no daughter cells formed

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What is a problem of chemotherapy?

  • they aren’t selective and target dividing cells = normal dividing body cells affected

e.g hair cells affected = hair loss

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What is secondary cancer?

  • parts of the tumour can break away if it isn’t enclosed in a membrane

  • The broken off section can move somewhere else through the blood or lymphatic system and grow another tumour

  • This is metastasis

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What is angiogenesis?

the cancer cells that make up a tumour attract blood vessels to grow into the tumour

These blood vessels nourish the tumour

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What is the difference between benign and malignant tumours?

Benign:

  • has a membrane

  • No metastasis

  • They put pressure on things (non invasive)

  • Non cancerous

  • Slow growing

Malignant:

  • no membrane

  • Metastasis

  • Secondary tumours are likely formed

  • Invasive

  • cancerous

  • Fast growing

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How is meiosis and mitosis different?

Mitosis produced 2 identical daughters cells whereas meiosis produced 4 non identical cells and form gametes

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What are haploid cells?

Sex cells that have only one copy of each chromosome from parents

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What are diploid cells?

Sex cells that have 2 copies of each chromosome from parents

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What is the process of meiosis?

  1. Before meiosis starts dna unravels and replicates forming chromatids

  2. DNA condenses forming sister chromatids joined by centromere

  3. Meiosis 1: chromosomes arrange into homologous pairs and then seperate

  4. Meiosis 2: sister chromatids making up each chromosome separated creating 4 haploid cells

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What is the advantage of meiosis?

Increases amount of genetic variation allowing survivors to pass on their successful gene combinations onto offspring

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What 3 ways can combinations of alleles be produced by?

  • independang assortment

  • Random fertilisation

  • Crossing over

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What is independent assortment?

Homologous pairs of chromosomes can be reshuffled in any combination during meiosis

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What is random fertilisation?

Any male gamete can join with any female gamete who each have chromosomes carrying different alleles

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What is crossing over (chiasmata)?

Homologous chromosomes line up together and the chromatids cross over each other and join together, the links are called Chiasmata

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What does non disjunction result in?

More than 2 copies of chromosomes being created → leads to disorders like Down syndrome

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What is genetic diversity?

The number of different alleles of genes in a species or population.

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When does evolution happen?

When the genetic composition (allele frequency) of a population changes over successive generations

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What is the structure for a natural selection question?

I solation mechanism

V ariation

A dvantageous

M utation

P ass it on

S eperate species

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What are the 3 main ways in which natural selection acts on the phenotypes in a population?

  1. Stabilising selection → always occurs in an unchanging environment and eliminated extreme variations and favours the average phenotypes e.g human birth mass

  2. Directional selection → favours the extreme phenotypes usually in a changing environment e.g antibiotic resistance

  3. Disruptive selection → favours 2 extreme populations causing a bimodal distribution , new species may arise due to accumulation of different mutations within a species

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What is allopatric and sympatric?

Allopatric = physical barrier separating the populations

Sympatric = no physical barrier

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What is the founder effect?

  • occurs when a few individuals from a population colonise a new region and give rise to populations that are genetically distinct from the populations they left behind → these new populations can then develop into new species over time

  • This new population shows less genetic diversity than the populations they came from

  • The seperate species they develop into over time is less able to adapt to changing conditions due to having fewer alleles

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What is classification?

The arrangement of organisms into groups of various sizes on the basis of shared features

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What is taxonomy?

A form of classification that focuses on physical similarities between different species

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What is phylogeny?

The classification of organisms by these evolutionary relationships, so that every group shares a common ancestor

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What are the basic forms of classification?

  1. artificial classification → divided organisms according to their differences that are useful to them e.g colour, size → however it ignores genetic info

  2. natural classification → divides organisms into according evolutionary relationships and into a hierarchy with no overlaps

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What is a phylogenetic tree?

Evolutionary history of organisms that shows their common ancestors → closely related organisms have diverged more recently from their common ancestor

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What are some examples in shared characteristics?

  • fossil records show similarities

  • Similarities in protein/ amino acid structure

  • Similarities in behaviour

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What are homologous structures?

Structural similarities that are inherited from a common ancestor e.g hands from cats, humans, frogs

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What are analogous structures?

Those with the same purpose thag have evolved independently due to similar evolutionary pressures e.g wing shape

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How does the binomial system name organisms scientifically?

  • genus (like last name) is the first letter of the first part of the name and is always capitalised and underlined when written

  • Species (like first name) is the second part and not capitalised but is underlined when written

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What are the advantages of using the binomial system?

  • for brevity → earlier systems used more descriptive terms so were much longer

  • It’s widespread → it is used internationally

  • For clarity → the same name for the same species despite its geographical spread

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What is the order of the binomial hierarchy?

  1. Domain

  2. Kingdom

  3. Phylum

  4. Class

  5. Order

  6. Family

  7. Genus

  8. Species

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What are the three subcategories in the domain division?

  1. archaea → simple single cells

  2. Bacteria → prokaryotic cells

  3. Eukaryota

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What are species?

2 organisms that are able to produce fertile offspring

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Why is it difficult to give a definite answer for species?

  • they change and evolve over time becoming new species

  • There can be considerable variation in the same species e.g dogs

  • Many species are extinct and left no fossil data

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How are evolutionary relationships determined?

by studying:

  • DNA sequences using DNA hybridisation

  • Anatomy e.g hologous features

  • Fossil records

  • Behaviour

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What do DNA comparisons allow us to do?

  • identify numbers and types of differences between species

  • The more closely 2 species are related, the shorter the amount of time has passed since they shared a common ancestor

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What are the steps to carry out DNA hybridisation?

  1. Hybrid strands soeafsfed and temperature is increased in stages

  2. At each stage the percentage of stow strands that are linked together are measured

  3. If 2 species are closely related they will share many complementary nucleotide bases

  4. The larger the number of hydrogen bonds, the stronger the hybrid strand will be

  5. The higher the temperature needed to split the hybrid strand, the more closely the two species are leafed and vice versa

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why is courtship behaviour carried out by organisms?

To attract a mate of the right species

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What are some simple courtship behaviours?

  • releasing a chemical e.g pheromones released

  • Using sound

  • Visual displays e.g male peacocks

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What are some complex courtship behaviours?

  • dancing

  • Building

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Why are courtship behaviours necessary?

  • to recognise members of their own species

  • To identify a mate capable of breeding

  • To form a pair bond

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What is the stimulus response chain order?

  1. Make communicates a courtships signal

  2. This acts as a visual stimulus for the female

  3. The females nervous system detects and responds with a specific behaviour of her own

  4. This acts as a stimulus to the male

  5. The male responds

  6. The cycle repeats