Gene Expression Flashcards

Question

Activator proteins

Answer 1

Bind to enhancer DNA sequences and switch transcription 'on' (up regulate structural gene expression).

Answer 2

Bind to silencer DNA sequences and switch transcription 'off' (down regulate structural gene expression).

Answer 3

It usually involves an enhancer region of DNA (located a fair distance upstream of a structural gene) folding back over and interacting with the promotor region near the structural gene. Transcription factors bind to promotor regions which enable RNA polymerase to bind here and initiate transcription. The enhancer region is a short regulatory sequence of DNA that works to enhance or speed up the rate of transcription. The promoter region is a length of DNA to which the RNA polymerase enzyme binds to initiate transcription (mRNA nucleotides being sequenced together using the DNA template).

Answer 4

The regulation of genes often involves operons. An operon is a length of DNA made up of structural genes and control sites (eg. operator and promotor regions, which are located 'upstream on 5' side' of the structural genes). The operator region is a regulatory DNA sequence that can act as a 'switch' and turn a gene on or off. The promoter region is a length of DNA to which the RNA polymerase enzyme binds to initiate transcription. In prokaryotic organisms regulatory genes, often found upstream of the operon, can make repressor proteins that bind to the operator region (only found in prokaryotic cells) and supress gene expression by preventing RNA polymerase binding to the adjacent promotor region.

Answer 5

Regulatory genes code for proteins called transcription factors that bind to regulatory DNA sequences (eg. ‘promotor’ regions, enhancers or silencers) upstream of structural genes. Transcription factors can either 'up regulate' (enhance) or 'down regulate' (supress) the transcription of a structural gene. Environmental factors can influence the addition of chemical tags (eg. methylation or acetylation) which influences the coiling of DNA and also transcription. (NOTE: Tightly coiled and highly methylated regions of DNA seem to be transcribed less). microRNA molecules can be produced from non-coding regions of DNA which influence translation at ribosomes. The use of chemical tags or microRNA in gene regulation is sometimes also referred to as Epigenetics.

Answer 6

On the Y chromosome there is a gene called the Sex Determining Region Y (SRY) gene. This gene produces a transcription factor (SRY) protein that upregulates the production of other transcription factors (eg. SOX 9) triggering the embryonic gonad tissue/ cells to differentiate and the gonad becomes a testis (seminiferous tubules develop and testosterone production begins). When no SRY protein is made, low SOX9 concentrations will not stimulate testis production so the embryonic gonad remains in the female form.

Answer 7

Body plan genes (the genes that control the development of body plans) are similar in plants, animals and fungi. The HOX genes are types of Homeotic (Homeobox) genes which are a collection of similar genes that are expressed in particular patterns at particular stages of development. They produce specific protein transcription factors. In animals, HOX genes control events such as the embryonic development of a head to tail axis, segmentation and the development of appendages/ limbs. Eg. HOX genes in insects specify which appendage grows from which body segment.

Answer 8

Any mechanism that alters gene expression without altering the DNA sequence. The epigenome refers to a system of gene control outside of the DNA ('above the genome') .

Answer 9

Involves the inheritance of traits transmitted by mechanisms not directly involving the DNA nucleotide sequence.

Answer 10

Example of an epigenetic process. Histone modification: how tightly coiled the DNA is around histones (and also how tightly packed nucleosomes are) is influenced by the presence or absence of specific chemical tags. DNA acetylation -acetyl groups are added to DNA which 'relaxes' histone structures and enhances transcription DNA methylation- the addition of methyl groups to the DNA at the start of a structural gene and will often reduce transcription. Influence gene expression via enhancing or suppressing transcription.

Answer 11

Example of an epigenetic process. Some small RNA sequences (approx. 22 nucleotides long) that can silence genes by either degrading mRNA or blocking translation at ribosomes. These microRNA molecules can interfere with protein synthesis by stopping translation (by attaching to mRNA and either blocking mRNA from being translated by ribosomes or by degrading mRNA).

Answer 12

A copy of the genetic code made from DNA in a single sided form, whose codons (3 base sequences) can be read and are used to make proteins. It carries the genetic information from the nucleus (via nuclear pores) to the ribosomes in the cytoplasm of the cell.

Answer 13

It is located in the cytoplasm of the cell, ribosomes are made up of ribosomal RNA. The ribosome exists as two subunits (a large and a small subunit). It directs the translation of mRNA into proteins which sits between the two subunits during translation.

Answer 14

It is located in the cytoplasm of the cell. It brings (transfers) amino acids to ribosomes during translation. It contains an anticodon that is complimentary to a three nucleotide codon of mRNA that is being decoded at the ribosome. The amino acids carried by tRNA can then be joined together and processed to make a polypeptide chain and proteins.

Answer 15

DNA Transcription RNA Translation Protein