Bio AT2 2023

Purines

Adenine and guanine, 2 fused rings

Pyrimidines

Thymine and Cytosine, 1 fused ring

5’ (5 prime)

Phosphate linked to 5th carbon in sugar

3’ (3 prime)

OH group linked to 3rd carbon in sugar

DNA replication step 2 (after unzipping)

Binding proteins attach to the exposed ends of each strand to prevent them from coming back together

What end is primer added to in DNA replication?

3’ end

What removes the RNA primers?

exonuclease

What is different about RNA’s sugar

Ribose, extra oxygen

What is different about the nucleotide bases of RNA?

Uracil instead of thymine

What does RNA polymerase bind to during transcription?

Promoter

What causes introns to form loops?

Small nuclear ribonucleic particles (snRPS)

What excises the introns?

Splicosomes

What sticks exons back together?

RNA ligase

Functions of proteins (6)

Development and repair

energy

hormones

enzymes

transport and storage

antibodies

What are prokaryotes’ version of histones?

Nucleoid-associated proteins

DNA methylation

A methyl group is added to the DNA which stops some genes from being expressed

Histone modification

Acetyl group is added, which loosens the DNA from being too tight around the histones, activates the gene

Order of the steps in mitosis / meiosis

Interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Mitosis interphase

The centrosomes and DNA duplicate

Mitosis Prophase

Centrosomes migrate to opposite poles, spindle fibres form

Mitosis metaphase

The spindle fibres align the sister chromatids along the equator of the cell

Mitosis Anaphase

The sister chromatids are separated, and brought to opposite poles

Mitosis telophase

A new nuclear membrane forms around the two groups of chromosomes

Mitosis cytokinesis

Cytoplasm is divided

Meiosis Interphase

DNA and centrosomes replicate

Meiosis prophase 1

Homologous pairs arrange themselves in tetrads, crossing over occurs, centrosomes migrate to either pole

Meiosis metaphase 1

The tetrads are arranged along the equator

Meiosis Anaphase 1

The HOMOLOGOUS CHROMOSOMES are separated and brought to opposite poles

Meiosis telophase 1

new nuclear membrane forms around groups of sister chromatids, then CYTOKINESIS

Meiosis prophase 2

nuclear membrane disintegrates

Meiosis metaphase 2

Sister chromatids are arranged along equator of cell perpendicular to how they were in meiosis 1

Meiosis Anaphase 2

Sister chromatids are separated and pulled to either pole

Meiosis telophase 2

new nuclear membrane forms, then CYTOKINESIS

Random segregation

It is random which cells get maternal vs. paternal chromosomes (alleles) during meiosis

Independent assortment

Its random whether the maternal goes on top of the paternal or the paternal goes on top of the maternal when they’re arranged in tetrads

Crossing over

When homologous chromosomes are arranged in tetrads, parts of them can form a chiasma, where sections of the chromosomes are exchanged

Recombitant chromatids

Due to crossing over they contain both maternal AND paternal alleles

What does SNP stand for?

Single nucleotide polymorphism

What is a SNP?

single nucleotide substitution

>1% of population = ?

SNP

Mutation

What must the environment ensure for fertilisation? (4)

Gametes can meet

Moisture

Food + shelter

Dispersal of young

Process of producing gametes

Gametogenesis

To sexually reproduce, organisms must be able to find a mate, therefore ? (2)

Must be a difference between species and between sexes

What environment uses external fertilisation

aquatic environments

How does the embryo receive nutrients in external fertilisation?

Direct diffusion between the water and the cell

Why are large numbers of gametes produced in external fertilisation?

Low chance of gametes meeting

How are chances of gametes meeting increased in external fertilisation? (3)

Cyclical reproductive behaviour

Synchronised gamete release

Mating behaviour

Drying out of gametes

dessication

What does more parental care result in?

Greater offspring survival chance, which means less offspring need to be produced at once

What do the leaves of bulbs store?

food

What does the terminal bud of a bulb do?

Produce a flower

What does the lateral bud of a bulb do?

Produce a new plant

What do rhizomes look like / where are they located?

Horizontal, underground

What does the terminal bud of a rhizome do?

Makes a flower

What does the lateral bud of a rhizome do?

Makes more rhizomes

What does a runner look like / where is it located?

Horizontal above ground

What do the terminal buds of a runner do once they touch the ground?

Make a new plant

What is unique about gymnosperms?

Their seeds are not housed in ovaries

What do the leaves of gymnosperms form?

Cones - can be male or female

What does the male cone of a gymnosperm produce?

Large amounts of pollen

What does a gymnosperm rely on for pollination?

Wind

Angiosperms

flowering plants

Function of petals

Advertise to pollinators

Function of sepals

Protect flower bud

Stamen structure

Filament tipped by anther x

What happens within the anther?

Sacs produce pollen via meiosis

What do pollen grains house?

Cells that develop into sperm

Carpal structure

Style with stigma

What is at the base of the carpal

The ovary

What is inside the ovary (flower)?

Ovules

What do ovules house?

Developing ova and supporting cells

Pistil

Single carpal or group of fused carpals

How are the male gametes of angiosperms produced?

Cells inside pollen sacs undergo mitosis

Pollination

Pollen moves from an anther to a stigma

What happens after pollen grain lands on the stigma?

A tube grows from the grain to an ovule. 2 male gametes go down the tube, one of them fertilises the ovum.

What does a fertilised ovule become?

Seed

What does the ovary become after fertilisation?

Fruit

Development of an angiosperm zygote stops until there are favourable environmental conditions, then ?

The seed germinates

Fungi vs plant

Cell wall but no chloroplasts or chlorophyll

Fungi structure

Hyphae

Mycelium

Sporangium

Hyphae

Long thin threads, make up fungi

Mycelium

Tangled web of hyphae

Sporangium

Capsule where spores are made

What division process makes spores?

Mitosis

Budding process

Outgrowth off parent organism, the parent nucleus divides and one of the nuclei move to the bud. The bud breaks off and becomes the new organism

Why would fungi choose to reproduce sexually?

Adverse environmental conditions

How do bacteria reproduce

Binary fission - cell forms DUMBBELL shape when doing this

Protists structure

unicellular or unicellular-colonial

How do protists reproduce?

Most by binary fission, some by budding

Ionising radiation energy

high

How can ionising radiation cause a mutation? (2)

If it hits DNA directly, it can break the covalent bonds between nucleotides causing the backbone to break. As DNA repair enzymes put the DNA back together, they may reassemble it in the wrong order

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It can also knock electrons out of orbit of nearby molecules, causing them to ionise. They are now called FREE RADICALS. These free radicals can react with nearby DNA, and may prevent transcription or translation, resulting in loss of control of the cell cycle

Non-ionising radiation energy

Low, only UVC can do any damage (UVA and UVB stopped by ozone)

How can UV radiation cause a mutation? (1)

It can cause adjacent thymine or cytosine bases on the same DNA strand to link together to form a dimer. These dimers cause structural kinks in the DNA, preventing transcription and translation and resulting in loss of control of the cell cycle.

How can chemical mutagens cause a mutation? (general)

Can be put into DNA instead of a nitrogenous base (because they are chemically similar)

How do deanimating agents cause mutations?

They can change one base to another one

How do viruses cause mutations?

They insert their DNA into the host genome to reproduce. If they insert their DNA in the vicinity of a gene, this can cause a mutation.

How does a retrovirus turn its RNA into DNA?

Reverse transcriptase

What is radon?

A radioactive gas

What does radon release to cause mutations?

Ionising radiation